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FERDINANDO TADDEI

Professore emerito
Dipartimento di Scienze della Vita

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Pubblicazioni

2008 - On the track of absolute enantioselective catalysis [Articolo su rivista]
L., Caglioti; B., Barabas; Faglioni, Francesco; Florini, Nicola; Lazzeretti, Paolo; Maioli, Marco; K., Micskei; K., Rabai; Taddei, Ferdinando; Zucchi, Claudia; Palyi, Gyula
abstract

The main goal of this communication is to show the utility of empirical approaches combined with mathematical methods in the research regarding the molecular basis of biological chirality. Preparative results (enantiomeric excesses, e.e.) obtained in asymmetric autocatalysis with (AAC) and without (AES) chiral additive were analyzed. Statistical calculations show, that AES (absolute enantioselective synthesis) experiments yield two independent groups of results with prevalence of the R- or S-enantiomer. These are distributed asymmetrically in a second-order beta distribution. Empirical calculations both on AAC and EAS enable to identify the very low (statistical) e. e.-s amplified by AES. These initial e. e.-s show normal distribution. Possible molecular-level reasons of these results were controlled by quantum chemical MO calculations and compatible mechanism(s) are discussed.

2007 - On the traces of absolute enantioselective synthesis [Relazione in Atti di Convegno]
B., Barabas; L., Caglioti; Faglioni, Francesco; Florini, Nicola; Lazzeretti, Paolo; Maioli, Marco; K., Micskei; G., Rabai; Taddei, Ferdinando; Zucchi, Claudia; Palyi, Gyula
abstract

The main goal of this communication is to show the utility of empirical approaches combined with mathematical methods in the research regarding the molecular basis of biological chirality. Preparative results (enantiomeric excesses, e.e.) obtained in asymmetric autocatalysis with (AAC) and without (AES) chiral additive were analyzed. Statistical calculations show, that AES (absolute enantioselective synthesis) experiments yield two independent groups of results with prevalence of the R- or S-enantiomer. These are distributed asymmetrically in a second-order beta distribution. Empirical calculations both on AAC and EAS enable to identify the very low (statistical) e.e.-s amplified by AES. These initial e.e.-s show normal distribution. Possible molecular-level reasons of these results were controlled by quantum chemical MO calculations and compatible mechanism(s) are discussed.

2003 - Formation and cleavage of aromatic disulfide radical anions [Articolo su rivista]
S., Antonello; K., Daasbjerg; H., Jensen; Taddei, Ferdinando; F., Maran
abstract

The electron transfer (ET) to a series of para-substituted diaryl disulfides, having the general formula (X-C6H4S-)2, has been studied. The X groups were selected as to have a comprehensive variation of the substituent effect, being X = NH2, MeO, H, F, Cl, CO2Et, CN, and NO2. The reduction was carried out experimentally, using N,N-dimethylformamide as the solvent, and by molecular orbital (MO) ab initio calculations. The ET was studied heterogeneously, by voltammetric reduction and convolution analysis, and homogeneously, by using electrogenerated radical anions as the solution electron donors. The reduction is dissociative, leading to the cleavage of the S-S bond in a stepwise manner. Both experimental approaches led us to estimate the Edegrees and the intrinsic barrier values for the formation of the radical anions. Comparison of the independently obtained results allowed obtaining, for the first time, a quantitative description of the correlation between heterogeneous and homogeneous rate constants of ETs associated with significant inner reorganization energy. The experimental outcome was fully supported by the theoretical calculations, which provided information about the disulfide lowest unoccupied MOs (LUMOs) and singly occupied MO (SOMO), the bond dissociation energies, and the most significant structural modifications associated with radical anion formation. With disulfides bearing electron-donating or mildly electron-withdrawing groups, the inner reorganization is particularly large, which reflects the significant stretching of the S-S bond experienced by the molecule upon ET. The process entails formation of loose radical anion species in which the SOMO is heavily localized, as the LUMO, onto the frangible bond. As a consequence of the formation of these sigma*-radical anions, the S-S bond energy of the latter is rather small and the cleavage rate constant is very large. With electron-withdrawing groups, the extent of delocalization of the SOMO onto the aryl system increases, leading to a decrease of the reorganization energy for radical anion formation. Interestingly, while the LUMO now has,pi* character, the actual reduction intermediate (and thus the SOMO) is still a sigma*-type radical anion. With the nitro-substituted disulfide, very limited inner reorganization is required and a pi*-radical anion initially forms. A nondissociative type intramolecular ET then ensues, leading to the formation of a new radical anion whose antibonding orbital has similar features as those of the SOMO of the other diaryl disulfides. Therefore, independently of the substituent, the actual S-S bond cleavage occurs in a quite similar way along the series investigated. The S-S bond cleavage rate, however, tends to decrease as the Hammett sigma increases, which would be in keeping with an increase of both the electronic and solvent reorganization energies.

2001 - Exocyclic push-pull conjugated compounds. Part 4. rotational barriers in poorly polarized push-pull ethylenes [Articolo su rivista]
Benassi, Rois; Bertarini, C; Taddei, Ferdinando; Kleinpeter, E.
abstract

The rotational barrier for substituted ethylenes was calculated with MO ab initio methods, both in the Hartree-Fock (HF) single determinant scheme and with multiconfigurational self-consistent field (MCSCF) approaches. The HF model affords reliable results only when applied to molecules substituted with strong electron donor groups, assigning a push-pull character to the molecule. The MCSCF approach was employed for calculating rotational barriers in poorly polarized ethylenes not directly amenable to the HF methods; however, this method was found hard to handle for low symmetry molecules with substituents interacting with the double bond. A method is proposed based on the interpolation of the energy of the perpendicular conformation from a Fourier truncated function constructed with HF molecular energies calculated for frozen conformations twisted up to 60 degrees, The application of HF theory for studying internal rotation in substituted ethylenes with poorly polarized character is discussed and an upper limit of 35-40 kcal/mol can be set up for having reliable barriers from the calculated energy of the rotational transition state at this level of theory. (C) 2001 Elsevier Science B.V. All rights reserved.

2001 - Ground-state molecular stabilization of substituted ethylenes. A theoretical mo ab-initio thermochemical study [Articolo su rivista]
Benassi, Rois; Taddei, Ferdinando
abstract

The origin of the rotational barrier around the partial C=C double bond in substituted ethylenes is discussed with reference to the stabilization of the conformational minimum (GS) and of the rotational transition state (TS). Molecules with different polar character of the double bond were chosen, ranging from ethylene to olefins with strong push-pull character. The enthalpies of hydrogenation, DeltaH(hydr.), and of formation, DeltaH(f)(0), of these molecules were employed to obtain the stability of GS; these thermochemical properties were calculated with MO ab-initio theory at HF/6-311G**//HF/6-311G** and MP2/6-311G**//HF/6-311G** levels and with CBS-4M model chemistry. The stabilization of TS was derived from the torsional potential for rotation around the C=C bond. The lowering of the energy content of GS of substituted ethylenes, referring to ethylene, is accompanied by an even greater stabilization of TS, thus a lowering of the rotational barrier with respect to ethylene is generally found in these molecules. (C) 2001 Elsevier Science B.V. All rights reserved.

2000 - Complete basis set model chemistry applied to molecules of increasing molecular complexity: Thermochemical properties of organic sulfur derivatives [Articolo su rivista]
Benassi, Rois; Taddei, Ferdinando
abstract

To estimate the thermochemical properties, bond dissociation energies and atomization energies of sulfur organic derivatives, the complete basis set (CBS) method was employed at the lower computational level (CBS-4) owing to the large molecular size of a number of the molecules chosen. By comparison with experimental values, calculated values of thermochemical properties are subject to error, which increases in line with the increase in molecular complexity. The main source of error affecting the calculated enthalpy of formation stems from the difference between the energy of the molecule and that of the single atoms: the greater the size of the molecule, the greater the accumulation of error. By acting on the empirical correction to the CBS energy and minimizing the error due to the contribution of the single atoms to the dissociation energy a parameter di for each atom i is obtained. Application of these corrections does not greatly affect the heats of formation of the small molecules included in test sets employed for previous comparisons of calculated and experimental values, while there is a great improvement in the case of large molecules, for example, diphenyl disulfide. The mean absolute deviation turns out to be 2.52, which is greater than that obtained in recent reexaminations of model chemistry methods Including the G3 and G3(MP3) approaches. The improvement in the results calculated for large molecules, whose heats of formation are calculated with large errors at the CBS-4 level, in comparison also with the CBS-4M version, justify our approach.

2000 - Exocyclic push-pull conjugated compounds. Part 1. Theoretical study of the effect of ring size on the structure, electronic properties and rotational barriers of cyclic analogoues of 1,1-diamino-2,2-dicyanoethylene [Articolo su rivista]
Benassi, Rois; Bertarini, C; Kleinpeter, E; Taddei, Ferdinando; Thomas, S.
abstract

An MO theoretical ab initio study was performed on 2-exo-methylene push-pull derivatives having as donor groups nitrogen atoms, components of a heterocyclic ring, and as acceptors CN and COOEt groups. Five-, six- and seven-membered ring derivatives were considered. Calculations were also performed on a number of push-pull ethylenes whose experimental properties were reported in the chemical literature in order to test the soundness of the conclusions from theoretical approaches. The physical properties calculated for the latter molecules were compared with known experimental values, in order to check the predictive ability of the theoretical approaches employed. Geometrical features and torsional barriers in solution are satisfactorily reproduced. Results were obtained with different basis sets, second-order Moller-Plesset theory, in order to perform comparisons at different theoretical levels with a view to carrying out calculations in larger molecular systems. The widest range of comparisons between calculated values for the different molecules were carried out at the HF/6-31G*//HF/6-31G* level. The origin of the torsional barrier for isomer interconversion as a function of the electronic properties of these molecules is discussed, in particular by examining the polarized character of the exo double bond. The role of the lone pairs of the nitrogen atoms in the push-pull mechanism is investigated, also in competition with an unsaturated bond within the ring. The different conjugation patterns that can be exploited within these molecules is examined within the donor-acceptor model and Natural Bond Orbital (NBO) theory. Empirical correlations are proposed in order to estimate dipole moments and absorption wavelengths for the family of push-pull olefins. (C) 2000 Elsevier Science B.V. All rights reserved.

2000 - Exocyclic push-pull conjugated compounds. Part 2. The effect of donor and acceptor substituents on the rotational barrier of push-pull ethylenes [Articolo su rivista]
Benassi, Rois; Bertarini, C; Kleinpeter, E; Taddei, Ferdinando
abstract

The energy of the rotational barriers and electronic structure of the transition state in substituted ethylenes are discussed in the light of the results obtained from different theoretical MO ab initio approaches. The 6-31G* basis set at Hartree-Fock (HF) level and with second-order Moller-Plesset perturbation theory (MP2) was employed, critical points were localized through Full geometry relaxation and characterized by vibrational analysis. A multiconfigurational approach (MCSCF) with different active spaces was also employed. For alkenes the correct rotational transition state is obtained only from the MCSCF approach, whereas for push-pull olefins the HF approach with correlation corrections at MP2 level provides correct answers for the internal rotation around C(sp(2))-C(sp(2)) bonds. The choice is more critical when only acceptor or donor groups are present, especially when change of hybridization occurs at the atoms at the edges of the C-C bond in the critical points. (C) 2000 Published by Elsevier Science B.V. All rights reserved.

2000 - Exocyclic push-pull conjugated compounds. Part 3. An experimental NMR and theoretical MO ab initio study of the structure, the electronic properties and barriers to rotation about the exocyclic partial double bond in 2-exo-methylene-and 2-cyanoimino-quinazolines and-benzodiazepines [Articolo su rivista]
Benassi, Rois; Bertarini, C; Hilfert, L; Kempter, G; Kleinpeter, E; Spindler, J; Taddei, Ferdinando; Thomas, S.
abstract

The structure of a number of 2-exo-methylene substituted quinazolines and benzodiazepines, respectively, 1, 3a,b, I (X = -CN, -COOEt) and their 2-cyanoimino substituted analogues 2, 3c,d (X = -CN, -SO2C6H4-Me(p) was completely assigned by the whole arsenal of 1D and 2D NMR spectroscopic methods, The E/Z isomerism at the exo-cyclic double bond was determined by both NMR spectroscopy and confirmed by ab initio quantum chemical calculations; the Z isomer is the preferred one, its amount proved dependent on steric hindrance. Due to the push-pull effect in this part of the molecules the restricted rotation about the partial C-2,C-11 and C-2,N-11 double bonds, could also be studied and the barrier to rotation measured by dynamic NMR spectroscopy. The free energies of activation of this dynamic process proved very similar along the compounds studied but being dependent on the polarity of the solvent. Quantum chemical calculations at the ab initio level were employed to prove the stereochemistry at the exo-cyclic partial double bonds of 1-4, to calculate thr barriers to rotation but also to discuss in detail both the ground and the transition state of the latter dynamic process in order to better understand electronic, inter- and intramolecular effects on the barrier to rotation which could be determined experimentally. in the cyanoimino substituted compounds 2, 3c,d, the MO ab initio calculations evidence the isomer interconversion to be better described by the internal rotation process than by the lateral shift mechanism. (C) 2000 Elsevier Science Publishers B.V. All rights reserved.

1999 - NMR spectroscopic and theoretical structural analysis of 5-benzyl substituted hydantoins in solution [Articolo su rivista]
Benassi, Rois; Bregulla, A; Henning, D; Heydenreich, M; Kempter, G; Kleinpeter, E; Taddei, Ferdinando
abstract

The vicinal H,H and H,C coupling constants along the Ph-CH2AB-CRHM-C-X(=O)R' spin system of 5-benzyl substituted hydantoins together with the results of accompanying force field (TRIPOS) and quantum chemical ab initio calculations (GAUSSIAN-94 with atomic basis set of 3-21G type) were employed to report on the rotamer population about the hydantoin C(5)-benzyl substituent bond. The conformation having the phenyl ring folded over the hydantoin ring system proved to be preferred. (C) 1999 Elsevier Science B.V. All rights reserved.

1998 - A theoretical study of the effects governing the internal rotation process in allyl derivatives [Articolo su rivista]
Benassi, Rois; Taddei, Ferdinando
abstract

Total molecular energy as a function of internal rotation around the C(sp(2))-C(sp(3)) bond, referred to as the C-C bond, in the molecules CH2=CHCY3, CH2=CHCH2Y, with Y = H, F, Cl, CH3, and CH2=CHCHY3, with Y = F, Cl, was calculated at the ab initio MO level, with the 6-31G* basis set. The molecular geometry was fully relaxed at fixed rotational angles phi. The potential energy profiles V(phi) were obtained with a truncated Fourier series and the V-n terms (n = 1-3) are derived and discussed. The C-C bond distances change on rotation and the highest values of the increment Delta d are found in the rotational maxima. For the molecules with the CY3 top the changes in Delta d are linearly related to the changes in total molecular energy Delta E-TOT, but with different slopes in the different molecules. The slopes seem to depend on the absolute length of the C-C bond, and while the Delta d behaviour within a molecule seems mostly dictated by hyperconjugative effects, the absolute length d is most probably determined by through-space effects. The elongation Delta d is due, in the majority of the molecules examined, to a decrease in attractive interactions (barrier of attractive type: in the rotational maxim., although in 3,3,3-trichloropropene and cis-1,3,3,3-tetrachloropropene the barrier is mostly of the repulsive type (increase in repulsive interactions). This kind of correlation is less statisfactory for tops of lower symmetry: in the molecules with the CH2Y top it would appear that the gauche-skew barrier is of the repulsive type, and the trans-skew barrier of the attractive type. The rotational behaviour of the total energy was also analyzed according to a model of factorization in energy components ascribed to different effects, identified in the first instance as hyperconjugative and through-space effects. The hyperconjugative effect of the groups examined, Delta E-x, calculated with the Natural Bond Orbital (NBO) approach, is similar to that found for the corresponding benzyl derivatives, yet slightly stronger. The rotational pattern of Delta E-x mirrors that of Delta E-TOT, even though it seems necessary to take into account the presence of other effects to explain peculiar differences between these patterns. The through-space effect was further factorized in the contribution of van der Waals, Delta E-vdW, and electrostatic, Delta E-el., interactions. For the calculation of Delta E-d from atomic charges different approaches were employed (Mulliken NBO, CHELPG), yet none afforded a Delta E-el. contribution quantitatively in agreement with the other factors. A qualitative description of the through-space effect of the groups considered is nevertheless attempted in order to suggest a combination of effects exerted by the susbtituents examined on the vinyl moiety, stemming from the theoretical treatment of these molecules.

1998 - NMR spectroscopic and theoretical structural study of 5-exo-methylene-substituted hydantoins [Articolo su rivista]
Benassi, Rois; Bregulla, A; Friedrich, A; Henning, D; Heydenreich, M; Mickler, W; Kleinpeter, E; Kempter, G; Schilde, U; Taddei, Ferdinando
abstract

The H-1 and C-13 NMR spectra of a series of 3-phenyl-5-exo-methylene-substituted hydantoins were recorded and assigned unequivocally by the various methods of 1D and 2D NMR spectroscopy. Employing the NMR parameters thus obtained, the NOEs between the different protons within the molecules and the results of accompanying semiempirical (AM1 and PM3, respectively) and ab initio (3-21G*) quantum chemical calculations, the tautomerism, the acidity, the redox potentials, the stereochemistry and the electron density distribution of the hydantoins were studied, In addition, the X-ray crystallographic structure of compound 1r is given and compared with the spectroscopic results,

1997 - A theoretical MO ab initio approach to the conformational properties and homolytic bond cleavage in aryl disulphides [Articolo su rivista]
Benassi, Rois; Fiandri, Gl; Taddei, Ferdinando
abstract

The structural and conformational properties of disulphides R-1-S-S-R-2, with R-1 = phenil ring (Ph) and R-2 = H,Me and Ph and, for a comparison, those of the disulphides with R-1,R-2 = H,Me were determined with MO ab initio calculations. The level of theory chosen was the 3-21G* with full geometry relaxation and electron correlation corrections at a second order Moller-Plesset perturbation scheme (MP2/3-21G*/MP2/3-21G*). This choice allowed a comparison of the properties calculated for the molecules containing alkyl and phenyl groups at the same level of theory. Ail the disulphides examined showed patterns of the potential energy for internal rotation with a minimum conformation of skew type and two maxima, one of cis and one of trans type, with the former representing the higher transition state for internal rotation. The effect of the R group is higher on the cis barrier and the effect of Me and Ph is respectively to increase and decrease the barrier, with respect to R=H. The bond energy required for homolitically breaking the bonds (BDE) in these molecules and in the radicals R-S-S was estimated both from calculated total molecular energies, and from heats of formation of the species involved in the dissociation processes. The BDE´s from the ab initio energies were found to have been largely underestimated, which applies to a different extent to the S-S, S-H and C-S bonds. For the S-S bond, the BDE´s calculated at the level of theory adopted here are proportional to values from experiments or from higher levels of theoretical approaches. For the disulphides with R-1,R-2 = H,Me, calculations were performed with the sophisticated Gaussian-2 (G2) scheme and the BDE´s obtained are very close to the most accurate determinations, showing that a high level of theory is necessary to obtain these quantities at a convenient level of confidence. The origin of the barriers for internal rotation and of the different bond strengths in the molecules and radicals containing the S-S bond was analyzed within the natural bond orbital (NBO) description of donor-acceptor interactions.

1997 - A theoretical approach to the factorization of the effects governing the barrier for internal rotation around the C(sp(2))-C(sp(3)) bond into alpha-substituted toluenes [Articolo su rivista]
Benassi, Rois; Taddei, Ferdinando
abstract

The effects governing the barrier for internal rotation in a number of alpha-substituted toluenes C6H5CH2X (X = Cl, F, CH3, C(CH3)(3), CF3, CCl3) and alpha,alpha-disubstituted toluenes C6H5CHX2 (X = Cl, Fl were interpreted using a model which factorizes the energy barrier into three components, namely, a) hyperconjugation, b) electrostatic effects and c) van der Waals interactions. The potential energy profiles for internal rotation of the CH2X and CHX2 rotors were calculated at molecular orbital MO ab initio level with a 6-31G* basis set and analysed by means of a truncated Fourier series in the V-2 and V-4 terms. The hyperconjugative contributions were estimated employing natural bond orbitals (NBO) derived from the 6-31G* wave functions in a scheme of acceptor-donor intramolecular interactions. The donor and acceptor hyperconjugative contributions, with respect to the pi system of the benzene ring, of each bond constituting the CH2X and CHX2 rotors were found to contribute additively to the hyperconjugative effect of the whole rotating group. Electrostatic effects and van der Waals interactions were tentatively estimated with empirical formulas. The separate contributions of these effects were compared, albeit at a qualitative level, with the total molecular energy and their relative weight discussed. The rotational barriers of benzylchloride and benzalchloride are mainly controlled by hyperconjugative effects. In benzylfluoride and benzalfluoride, the hyperconjugative effects are active to the same extent as in chlorine derivatives but the barrier is mainly controlled by electrostatic effects. In the compounds with bulky X groups (X = C(CH3)(3), CF3 and CCl3), hyperconjugation plays a less important role than van der Waals interactions and electrostatic effects, and the relative weight of these effects differs for the substituents examined.

1997 - Ab initio MO study of the internal rotation process in alpha-chlorinated picolines. [Articolo su rivista]
Benassi, Rois; Bertarini, C; Taddei, Ferdinando
abstract

Conformational properties and barriers to internal rotation for the three isomeric picolines mono- bi- and trichlorosubstituted at the methyl group were studied at the theoretical level with ab initio MO calculations. Energy profiles for internal rotation of the chlorinated methyl group were obtained at the 6-31G* level with full molecular geometry relaxation, and the energy of critical points was recalculated at the MP2/6-311G** level of theory. The conformational minima and maxima of these derivatives are qualitatively similar to those found for benzene derivatives, yet differences are found in the heights of the barriers to internal rotation and in the presence of two rotational minima or maxima in the molecules with lower rotational symmetry. The origin of the barriers to rotation and of the different energy content of conformational minima is discussed in the light of the natural bond orbital (NBO) approach within the donor-acceptor viewpoint of intramolecular interactions, and electrostatic interactions between the rotating group and the ring.

1997 - Reductive electron transfer on trichloromethyl derivatives of benzene and pyridine studied by electrochemical methods [Articolo su rivista]
Borsari, Marco; Dallari, D; Fontanesi, Claudio; Gavioli, Giovanna; Iarossi, Dario; Piva, R; Taddei, Ferdinando
abstract

The electrochemical reduction of alpha,alpha,alpha-trichlorotoluene (benzotrichloride) and of the corresponding isomeric pyridine derivatives has been investigated by cyclic voltammetry and microcoulometry. Three irreversible diffusion controlled reduction waves have been observed in the voltammetry of the trichloromethyl derivatives and are found to correspond to the progressive two-electron reduction of derivatives where a chlorine atom is substituted by a hydrogen atom. The peak potentials E-p show that reduction of the pyridine derivatives is easier than that of the benzene derivatives with the same number of chlorine atoms, the more positive shift occurring for the 4-substituted compounds. The experimental findings would indicate a concerted electron transfer-bond breaking (C-Cl) mechanism for all the compounds examined, as well as for the chloromethyl and dichloromethyl derivatives formed after Cl/H substitution. Electron uptake appears to be the rate-determining step of the reductive cleavage of these molecules. The effects of the different aromatic rings and of the degree of halogen substitution of the methyl group on the reduction potentials are discussed.

1995 - CRYSTAL AND MOLECULAR-STRUCTURE OF Z- AND E-1,2-DICHLORO-1,2-BIS(2-CHLOROPHENYL)ETHYLENE. AN X-RAY AND NMR STUDY [Articolo su rivista]
Antolini, Luciano; Folli, Ugo; Iarossi, Dario; Mucci, Adele; Sbardellati, S; Taddei, Ferdinando
abstract

The crystal structures of the title compounds were determined by single crystal X-ray diffraction techniques. The molecule of the Z isomer, which crystallizes in the monoclinic space group C2/c with Z = 4 in a cell of dimensions a = 14.891(2), b = 10.780(2), c = 8.769(1) Angstrom, beta = 97.47(2)degrees, V = 1395.7(7) Angstrom(3), has crystallographic twofold symmetry. The E form crystallizes in the orthorhombic space group Pbca with a = 11.730(1), b = 6.932(1), c = 16.841(1) Angstrom, V = 1369.4(2) Angstrom(3), and Z = 4, Its molecules have crystallographically dictated 1 symmetry. In both isomers the phenyl rings are roughly perpendicular to the average ethylene plane. The atoms characterizing this plane show significant deviations from planarity in the Z isomer. Marked bond-angle distortions at the ethene carbons of both structures are observed. The H-1 and C-13 NMR spectra of the compounds were measured and, particularly in the case of the H-1 chemical shifts, fall into two quite separate spectral regions. At low temperature, two conformational isomers, those with different relative orientation of the C-Cl bonds of the phenyl rings, are observed in the spectrum of each compound.

1995 - Effect of ortho substituents on the internal rotation processes and conformational preferences of 1,2-diaryl-1,1,2,2-tetrachloroethanes: A 1H and 13C NMR variable temperature and x-ray structural study [Articolo su rivista]
Antolini, L.; Folli, U.; Iarossi, D.; Mucci, A.; Sbardellati, S.; Taddei, F.
abstract

The conformational behaviour of 1,2-diaryl-1,1,2,2-tetrachloroethanes, ortho,ortho'-disubstituted with CN (1), F (2) and CO2CH3 (3), and of the mesityl derivative (4), has been studied in solution by variable temperature H-1 and C-13 NMR spectroscopy. The internal rotation processes around the exocyclic C-C and central C-C bonds appear to have similar energy barriers and thus behave differently from the compounds without ortho substituents, studied previously, which have a higher barrier for the interconversion of anti/gauche conformers. At low temperature, compounds 1-3 exist as mixtures of gauche and anti conformers with the former prevailing; compound 4 is almost exclusively in the gauche form. The solid state crystal and molecular structure has been determined for compounds 2 and 3. The molecule of compound 2 has point symmetry ($) over bar 1, which defines perfect staggering around the central C-C bond with the aromatic rings anti. The structure is affected by statistical disorder due to two alternate orientations of the phenyl rings. The crystal structure of compound 3 indicates one asymmetrical molecule in a gauche conformation. Statistical disorder involves both the methoxycarbonyl substituents at the phenyl rings; these latter display almost the same orientation with respect to the C(sp(3)) carbons, in both compounds.

1995 - INTERNAL-ROTATION AROUND SINGLE BONDS AND CONFORMATIONAL PREFERENCES IN HETEROCYCLIC-ANALOGS OF BENZYL METHYL SULFOXIDE STUDIED WITH NMR TECHNIQUES [Articolo su rivista]
Folli, Ugo; Iarossi, Dario; Mucci, Adele; Taddei, Ferdinando
abstract

The conformational equilibrium related to the internal rotation processes occurring in sulphoxides of the type ArCH2SOCH3 (where Ar=2-thienyl, 2-furyl, 2-pyridinyl and (3-methyl)2-pyridinyl rings) were studied with H-1 and C-13 NMR spectroscopy. Proton chemical shifts and long-range coupling constants (n)J(H, H) were obtained from the iterative analysis of the multiplets and were employed, together with C-13 chemical shifts, long-range (n)J(C, H) and relaxation parameters (NOE and non-selective T-1 values) to obtain stereochemical relationships between the protons present in these molecules. Conformational predictions at a qualitative level were also derived from total molecular energies calculated with the semi-empirical AM1/MNDO method as a function of internal coordinates. The different approaches converged to indicate that the heterocyclic rings adopt an average orientation similar to the perpendicular orientation of the phenyl ring in benzyl methyl sulphoxide and, as regards rotation around the CH2-S bond, the prevalent conformer shows that the methyl group is symmetrically oriented with respect to the methylenic protons, The barriers for internal rotation are rather low and the equilibrium between conformers is dependent on the medium properties. Attempts to obtain conformational results were performed for the molecule of omeprazole, an antiulcer drug which contains the ArCH2SO-R moiety (Ar and R are substituted 2-pyridinyl and 2-benzimidazolyl groups, respectively). With respect to the other compounds examined, the orientation of the Ar ring does not significantly differ and the benzimidazole ring seems to prefer an orientation stereochemically equivalent to that of the methyl group.

1994 - INTERNAL-ROTATION AND CONFORMATIONAL PREFERENCES IN 1,2-DIARYL DERIVATIVES OF 1,1,2,2-TETRACHLOROETHANE - A H-1 DNMR AND X-RAY STRUCTURAL STUDY [Articolo su rivista]
Antolini, Luciano; Folli, Ugo; Mucci, Adele; Sbardellati, S; Taddei, Ferdinando
abstract

The title compounds show in their H-1 NMR spectra recorded at room temperature signals of different line-width characteristic of molecules with slow internal rotation around sterically crowded single bonds. From the DNMR study in [H-2(6)]acetone solution of the 4,4'-(compound 1) and 3,3'-bis(benzoic acid) dimethyl ester (compound 2) and of the 3,3'-bispyridine (compound 3) derivative the dynamic parameters of two internal rotation processes, with different energies of activation. were extracted. The internal rotation process with higher energy barrier (Delta G* = 13-14 kcal mol(-1)) was assigned to the anti reversible arrow gauche conformer interconversion, and that with lower energy barrier (Delta G* = 8-9 kcal mol(-1)) to the rotation of aromatic rings around the C(sp(3))-C(sp(2)) bond in the gauche conformer. The conformer populations measured at low temperature showed that the gauche conformer is the more abundant. The structural features of the conformers of compounds 1-3 were also investigated theoretically at a semi-empirical level with the AM1/MNDO method. The results of these calculations show that the anti conformer is the most stable one, yet the gauche form has higher polarity and this result could explain the increase of the gauche population in polar solvents. For compound 3 calculations were extended to the whole energy hypersurface having as coordinates the angles of rotation around the central C(sp(3))-C(sp(3)) and C(sp(3))-C(sp(2)) bonds. The theoretical free-energies of activation, even if largely underestimated, show that the barriers for the different internal processes follow the order: barrier for rotation around the C(sp(3))-C(sp(3)) bond > barrier for rotation around the C(sp(3))-C(sp(2)) bond in the gauche conformer > barrier for rotation around the C(sp(3))-C(sp(2)) bond in the anti conformer. This order fits the trend of the first two barriers. experimentally determined. For compound 3 and for the 4,4'-bisbenzonitrile (compound 4) derivative, the crystal and molecular structure was obtained from X-ray analysis: the molecules have crystallographically dictated 1 symmetry with perfectly staggered anti conformation. Longer C-Cl bond lengths and smaller Cl-C-Cl bond angles than those present in structurally similar compounds indicate steric crowding around the C(sp(3))-C(sp(3)) bond. Solid state conformations are in excellent agreement with the calculated ground-state rotational structure of these molecules.

1993 - Electron Transfer in the Reactions of Organic Trichloromethyl Derivatives with Iron(II) Chloride [Articolo su rivista]
Cornia, Andrea; Folli, Ugo; S., Sbardellati; Taddei, Ferdinando
abstract

Reduction of trichloromethyl derivatives RCCl3 [1, R = Ph;2, R = PhC(O); 3, R = EtOC(O)] with iron(II) chloride in acetonitrile, has been studied in order to examine the mechanism of the electron transfer (ET) process and the reactions of the radicals formed. Substrates 1-3 afforded different product compositions and the cause was identified as differences in the reactivity of radicals which is substantially of two types: reductive coupling and proton abstraction after further reduction to a carbanion coordinated to the metal ion. Compound 1 gave only coupling products, compound 2 only hydrogenated products and compound 3 a mixture of coupling and hydrogenated products depending on experimental conditions. Proton abstraction by the carbanion was found to occur from water molecules, which should be present in the coordination shell of the metal ion, and not from the solvent. The different behaviour of compounds 1-3 is attributed to the presence of substituents which are able to stabilize the radical and carbanionic intermediates. Rate constants at different temperatures were measured and the activation parameters calculated. The three substrates differ only slightly in reaction rates, in the order 1 > 2 > 3. Activation enthalpies are very close to each other and this agrees with the almost equal values of C-Cl bond dissociation energies of compounds 1-3, empirically determined. Large, negative entropies of activation were found, suggesting that an ordered activation complex should be formed in order that electron transfer from the metal ion to the organic halide can take place.

1992 - CRYSTAL AND MOLECULAR-STRUCTURES OF RING-SUBSTITUTED METHYL PHENYL SULFOXIDES - AN X-RAY AND MOLECULAR-ORBITAL ABINITIO INVESTIGATION [Articolo su rivista]
Ianelli, S; Musatti, A; Nardelli, M; Benassi, Rois; Folli, Ugo; Taddei, Ferdinando
abstract

The solid-state crystal and molecular structure of a number of ring-substituted methyl phenyl sulfoxides, containing mainly fluorine substituents, has been obtained by X-ray analysis. The conformation found for the molecules has geometrical features very close to those of the most stable conformer(s) predicted by ab initio molecular orbital calculations. In those compounds without ortho substituents the S = O bond is only slightly twisted from being coplanar with the ring plane, while a larger twist is present when both ortho positions are substituted. In the presence of one ortho substituent the S = O bond adopts an anti orientation and is almost coplanar with the ring. With the unsymmetrically substituted derivatives two conformers are possible and in the case of ortho substitution the energy difference (18-24 kJ mol-1) is large enough to have crystals only of the lower energy conformer. When the ortho positions are both free, the energy difference is quite low (0.6 kJ mol-1) and both conformers are found in the same crystal.

1991 - CONFORMATIONAL PREFERENCE OF THE METHYLSULFINYL GROUP BONDED TO THE FURAN AND THIOPHENE RINGS - A THEORETICAL APPROACH [Articolo su rivista]
Benassi, Rois; Folli, Ugo; Mucci, Adele; Schenetti, Luisa; Taddei, Ferdinando
abstract

The ground state conformations and transition states for conformer interconversion in the two isomers of the of furan (1 and 2) and thiophene (3 and 4) were identified through a theoretical approach based on ab-initio molecular orbital calculations. Two minima and two transition states were found in the potential energy profiles for all the molecules, but the behaviour of 2-methylsulphinyl furan (1) differs somewhat from that of the other compounds. The minima correspond to the two orientations of the S-O bond with respect to the heterocyclic heteroatom X (X = O or S), labelled X,O-cis an X,O-trans. The conformer having the S-O bond oriented s-cis with respect to the internal double bond with higher pi density (X,O-cis for the 3-methylsulphinyl derivatives and X,O-trans for the 2-methylsulphinyl derivatives) has a twist angle phi (between the S-O bond and the heterocyclic ring) of a few degrees. Larger distortions are present in the conformers with opposite orientation of the S-O bond, and the twist angle has the highest value (phi = 62.8-degrees) in compound 1. The transition states correspond to the methyl group being nearly coplanar with the heterocyclic ring and this situation seems to be due mostly to a loss of pi electron delocalization. More complex is the transition state situation for compound 1, since a barrier in the potential energy for internal rotation is imposed also by the repulsion between the heterocyclic and sulphinyl oxygen atoms. The conformer populations were estimated from the potential energy

1991 - CRYSTAL AND MOLECULAR-STRUCTURE OF CIS-[DICHLOROBIS(METHYL PHENYL SULPHOXIDE)]PLATINUM(II) AND CIS-[DICHLOROBIS(BENZYL METHYL SULPHOXIDE)]PLATINUM(II) - AN X-RAY AND NMR SPECTROSCOPIC STUDY [Articolo su rivista]
Antolini, L; Folli, U; Iarossi, D; Schenetti, Luisa; Taddei, Ferdinando
abstract

Reactions of (R,S)-methyl phenyl sulphoxide and (R,S)-benzyl methyl sulphoxide with K2PtCl4 give diastereomeric mixtures of cis-L2PtCl2 complexes. The mixtures isolated from the reactions, change their composition when allowed to stand in solution, to give, at equilibrium, ratios of +/- and meso forms which differ as a function of the sulphoxide employed. The crystal structure of one of the diastereoisomers isolated in the case of the complex obtained from (R,S)-methyl phenyl sulphoxide is built up from racemic pairs of discrete molecules with R,R and S,S configurations at chiral sulphur atoms. The crystals of the complex prepared from (S)-benzyl methyl sulphoxide contain two crystallographically independent but chemically equivalent molecules with S,S absolute configuration at sulphur atoms, and one methanol solvate molecule. In both complexes the metal atom shows cis square-planar coordination geometry of the two chlorine and two sulphur atoms from the organic ligands. The complexes show differences in the orientation of the sulphoxide ligands with respect to the co-ordination plane. The NMR parameters obtained at H-1, C-13 and Pt-195 frequencies provide useful indications for recognizing +/- and meso forms of platinum(II) complexes of sulphoxides and also contain information on the relative conformational patterns of the free and complexed ligands.

1991 - CRYSTAL AND MOLECULAR-STRUCTURE OF METHYLSULFINYL DERIVATIVES OF FURAN AND THIOPHENE BY X-RAY-DIFFRACTION [Articolo su rivista]
Folli, Ugo; Iarossi, Dario; Mucci, Adele; Musatti, A; Nardelli, M; Schenetti, Luisa; Taddei, Ferdinando
abstract

An investigation of the solid-state conformational properties of 3-methylsulphinyl derivatives of furan and 2- and 3-methylsulphinyl derivatives of thiophene, which also contain halogen atoms in the heterocyclic ring, is reported. For 3-iodo-2-(methylsulphinyl)thiophene, compound 1, two crystallographically independent molecules were found in the unit cell, and in 2-bromo-4-iodo-3-(methylsulphinyl)thiophene, compound 5, a high degree of disorder is present. The sulphur atom of the methylsulphinyl group has a pyramidal structure. The methyl group is highly twisted with respect to the ring plane and the S-O bond adopts different orientations in the molecules examined. When only one halogen atom is present in the ring the S-O bond is directed to the opposite side of the ring with respect to this atom, yet the relative position of the substituents determines a different twist of this bond with respect to the heterocyclic plane.

1991 - Conformational analysis of methylsulphinyl derivatives of furan and thiophene by employing nuclear magnetic relaxation and lanthanide induced shifts [Articolo su rivista]
Folli, Ugo; Iarossi, Dario; Mucci, Adele; Schenetti, Luisa; Taddei, Ferdinando
abstract

Relaxation parameters such as nuclear Overhauser effect (NOE) and spin-lattice relaxation times (T1) were applied to the conformational analysis of methylsulphinyl derivatives of furan and thiophene. Correlation times for molecular tumbling tau-c, and for methyl reorientation, tau-i, were obtained. The tau-i values for the different molecules examined are nearly the same, the tau-c are twice as large in derivatives that also contain an iodine substituent in the heterocyclic ring. From non-selective, selective and bi-selective T1 measurements and NOE values, relative to H-1 nuclei, and a best-fit procedure, the most probable conformational intervals for the methylsulphinyl group were located. Owing to the pyramidal structure of sulphoxides, the preferred conformers could not be fixed unambiguously. From the Lanthanide Induced Shift (LIS) technique on H-1 and C-13 nuclei, intervals of preferred orientations of the S-O bond with respect to the heterocyclic ring were found. Reliable conclusions about the conformational behaviour of these molecules have been drawn by matching the two sets of results. Relaxation parameters turn out to be useful for conformational analysis of small molecules when employed as a complementary tool with other experimental approaches.

1991 - PREFERRED ORIENTATIONS OF THE S-O BOND IN METHYLSULFINYL DERIVATIVES OF FURAN AND THIOPHENE - AN EXPERIMENTAL-STUDY BASED ON H-1, C-13, AND O-17 NMR-SPECTROSCOPY [Articolo su rivista]
Benassi, Rois; Folli, Ugo; Iarossi, Dario; Mucci, Adele; Schenetti, Luisa; Taddei, Ferdinando
abstract

The preferred conformations of the methylsulphinyl group bonded to the heterocycles furan and thiophene have been studied with NMR techniques in solution. The presence of one halogen atom ortho to the methylsulphinyl group determines the orientation of the S-O bond in the opposite direction with respect to the halogen, and the degree of coplanarity of this bond with the ring depends on the substitution-pattern. The higher degree of coplanarity is found when the methylsulphinyl group and the halogen substituent are in position 3 and 4. Two ortho substituents determine structures with large twists of the methylsulphinyl group. The chemical shifts of H-1, C-13 and O-17 nuclei of the methylsulphinyl group and referred to spectra in solution do not evidence trends of general validity for all the compounds examined as a function of the orientation of the methylsulphinyl group with respect to the ring. Such trends were present in the case of the corresponding phenyl derivatives. Nevertheless, by examining the behaviour of long-range (n)J(C,H) coupling constants, involving the carbon nucleus of the methyl group, together with chemical shifts, conclusions regarding the conformational behaviour of these molecules in solution can be derived. Possible perturbations of the equilibrium caused by the polarity of the medium are evidenced as well. The results indicate that in the 2-methylsulphinyl

1990 - CONFORMATIONAL ANALYSIS OF METHYL PHENYL SULFOXIDES CONTAINING FLUORINE SUBSTITUENTS IN THE PHENYL RING BASED ON H-1, C-13 AND O-17 NMR CHEMICAL SHIFTS AND LONG-RANGE nJ(HF) AND n(CF) COUPLING CONSTANTS [Articolo su rivista]
Benassi, Rois; Folli, Ugo; Iarossi, Dario; Mucci, Adele; Schenetti, Luisa; Taddei, Ferdinando
abstract

A conformational study on methyl phanyl sulphoxides, carrying different subtituents on the phenyl rings, based on the interpretation of H-1, C-13 AND O-17 NMR chemical shifts and long range J(H,F) and J(C,F) coupling constants is reported

1989 - AN MCSCF AB INITIO STUDY OF C-CL BOND CLEAVAGE IN H3C-Cl [Articolo su rivista]
Benassi, Rois; F., Bernard1; A., Bottoni; M. A., Robb; Taddei, Ferdinando
abstract

The thermal, photochemical and reductive dehalogenations of methyl chloride (H3C-Cl) are studied with the ab initio MCSCFmethod using three different basis sets (3-2 lG*, 6-31G* and 6-31 +G*). It has been found that both thermal and photochemicaldecomposition produce a methyl and a chlorine radical. The photochemical decomposition involves excitation of the H3C-Clmolecule from the singlet ground state to a singlet or triplet n-u* state which dissociates directly to these products. The reductivedehalogenation involves the formation of a metastable anion (resulting from electron transfer to the chloromethane) which dissociatesimmediately to a methyl radical and chloride anion. While for the thermal and photochemical decomposition the resultsobtained at the various computational levels do not significantly differ, for a reliable description of the reductive dehalogenation,it is essential to use a basis set, such as 6-31 +G*, which includes appropriate sp-type diffuse functions

1989 - Conformational Study of Substituted Methyl Phenyl Sulphoxides. A Multinuclear (1H, 13C and 17O) Approach., J. Chem. Soc. Perkin Trans. 2, [Articolo su rivista]
Benassi, Rois; Folli, Ugo; Iarossi, Dario; Mucci, Adele; Schenetti, Luisa; Taddei, Ferdinando
abstract

A number of ring-substituted methyl phenyl sulphoxides have been examined with a multinuclear n.m.r. approach in order to obtain experimental evidence of the conformational properties of the methylsulphinyl group bonded to an aromatic ring. Measurements were performed of 1H, 13C, and 17O chemical shifts and LIS (lanthanide-induced shifts) on 1H and 13C, long-range 13C–1H coupling constants. Each of these approaches by itself is not fully conclusive in showing the orientation of the SO bond in the different compounds examined, but by using them in combination a sound picture of the conformational behaviour of these molecules in solution can be obtained. The SO bond is thus almost coplanar with the aromatic ring in ortho-substituted compounds and oriented in the opposite direction with respect to the substituent. The twist-angle probably differs slightly as a function of the ortho-group. An increasing degree of distortion from coplanarity is found in para-substituted derivatives and ortho-disubstituted compounds. As regards 17O chemical shifts, these were found to span a smaller range than in the corresponding acetophenones.

1989 - Conformational preference in methyl phenyl sulphoxide and in ortho substituted fluorine derivatives: a theoretical approach [Articolo su rivista]
Benassi, Rois; Mucci, Adele; Schenetti, Luisa; Taddei, Ferdinando
abstract

Ab initio MO calculations (3-21G*//3-lG* basis set) have been performed for methylphenyl sulphoxide ( 1) ,2-fluoro- (2 ) and 2,6-difluoro- (3 ) derivatives in order to examine the structuralproperties of their conformational ground state (8). The conformational energy profile for rotation around the C,,-S bond has been constructed in the STO-3G* basis set and the minima have been located at the 3-21G* level allowing relaxation of the geometrical parameters of the methylsulphinyl group. For methylphenyl sulphoxide one energy minimum is found and corresponds to the SO bond nearly eclipsed with the phenyl ring (twist angle 7.31” ). Two energy minima are found for compound 2 and in the more stable conformation the SO bond is coplanar with the ring and anti with respect to the ortho fluorine substituent. In the less stable ground state the lone pair of the sulphur atom settles in the nodal plane of the n-electron cloud of the phenyl ring. This conformation is structurally close to the conformational ground state of compound 3. For compound1 the properties of the transition state have also been determined at the 3-21G* level. The energy barrier for internal rotation corresponds to the S-C bond of the methyl sulphinyl group eclipsed with one ortho C-H bond. The origin of the conformational ground- and transition-states in thesemolecules is discussed on the basis of their electronic structure.

1988 - L’equilibrio conformazionale del gruppo metilsolfinilico legato ad anelli aromatici ed eteroaromatici [Articolo su rivista]
Benassi, Rois; Folli, Ugo; Iarossi, Dario; Mucci, Adele; Schenetti, Luisa; Taddei, Ferdinando
abstract

L’equilibrio conformazionale del gruppo metilsolfinilico legato ad anelli aromatici ed eteroaromatici è stato studiato tramite risonanza magnetica nucleare e metodi teorici.

1987 - Costanti di accoppiamento a lungo raggio 13C-1H nell’analisi conformazionale di 3-formil derivati del furano e del tiofene [Abstract in Atti di Convegno]
Benassi, Rois; Folli, Ugo; Mucci, Adele; Schenetti, Luisa; Taddei, Ferdinando
abstract

Le costanti di accoppiamento13C-1H a lungo raggio sono state utilizzate nell’analisi conformazionale di 3-formil derivati del furano e del tiofene.

1987 - Long-range 13C-1H Spin-Spin Coupling Constants in the Conformational Analysis of Formil Derivatives of Furan and Thiophene, Magn. Reson. Chem., 25, 804-810 [Articolo su rivista]
Benassi, Rois; Folli, Ugo; Mucci, Adele; Schenetti, Luisa; Taddei, Ferdinando
abstract

The long-range 13C-1H Constants were employed in the conformational analysis of formil derivatives of furan and thiophene

1984 - A 1H NMR Spectra of the 2-Trifluoroacetyl Derivatives of Benzo[b]furan and Benzo[b]thiophene [Articolo su rivista]
Benassi, Rois; Folli, Ugo; Iarossi, Dario; Schenetti, Luisa; Taddei, Ferdinando
abstract

Proton magnetic resonance spectroscopy of title compounds were carefully examined.

1984 - Conformational Analysis f Organic Carbonyl Compounds. Part 3. A 1H and 13C Nuclear Magnetic Resonance Study of Formyl and Acetyl Derivatives of Benzo[b]furan [Articolo su rivista]
Benassi, Rois; Folli, Ugo; Iarossi, Dario; Schenetti, Luisa; Taddei, Ferdinando
abstract

A conformational study of formyl and acetyl derivatives of benzo[b]furan provides evidences that in the case of 2- and 7-derivatives, the E,Z-conformational mixture is solvent dependent: the Z prevailing in solvent with higher polarity.

1983 - Conformational Analysis f Organic Carbonyl Compounds. Part 3. A 1H AND 13C Nuclear Magnetic Resonance Study of Formyl and Acetyl Derivatives of Benzo[b]thiophene [Articolo su rivista]
Benassi, Rois; Folli, Ugo; Iarossi, Dario; Schenetti, Luisa; Taddei, Ferdinando
abstract

The conformational analysis of formyl and acetyl derivatives of benzo[b]thiophen was carried out by employing nmr chemical shifts (1-H and 13-C) and coupling constants. By measuring the lanthanide-induced shifts (LIS) and simulating experimental chemical shifts the relative conformer stability was determined. The results show that all the molecules examined are present almost completely in the Z conformation and that the stabilization of one conformer in this heterocyclic system seems due almost exclusively to the mesomeric interaction originating in the trans-arrangement of the C=O bond and the C=C bond having the higher double-bond character.

1983 - Conformational Analysis of 5-Membered Ring Compounds having Cholinergic Activity [Articolo su rivista]
Benassi, Rois; Schenetti, Luisa; Taddei, Ferdinando; L., Villa; V., Ferri
abstract

A study of the conformational properties, both referred to the heterocyclic ring and to the ammonium sustituent, has been carried out on dimethylaminomethylmethiodide derivatives of 2-methyl substituted 5- membered satyrated hetrocycles having cholinergic activity. The experimental employed is NMR of the proton: the spectra were fully analyzed and all the multiplet parameters tentatively assigned. Vicinal coupling constants were employed for the conformational study by introducing them in a best fit procedure between experimental and calculated (by a semi-empirical method) values. The molecular conformation thus obtained were compared with results previously obtained for a few of the compounds here examined or for similar systems and employed for discussing the possible factors relating molecular geometry to their biological activity.

1981 - Conformational Behaviour of Organic carbonyl Compounds. Part 2. Aldehydes and Acetyl Derivatives of Condensed Aromatic Hydrocarbons [Articolo su rivista]
Benassi, Rois; Iarossi, Dario; Folli, Ugo; Schenetti, Luisa; Taddei, Ferdinando
abstract

The relative conformer stability in a number of acetyl and formyl derivatives of condensed hydrocarbons has been determined by the lanthanide induced shift (LIS) method and by simulating the experimental chemical shifts. For the aldehyde of naphtalene the conformational results were confirmed by examining the nmr spectra of model compounds with known probable conformation. In condensed hydrocarbons containing carbonyl substituents the behviour found may be substantially related to three distinct situations, those comparable to the alpha- and beta -positions of naphtalene and overcrowded positions comparable to position 4 in phenanthrene. Calculation of the conformational behaviour by the semi-empirical methods provide qualitative correct results only for systems where steric interactions are small.

1980 - NMR Spectra, MO Calculations of Spin-Spin Coupling Constants and Conformational Analysis od Substituted 1,3-Dioxolanes [Articolo su rivista]
Benassi, Rois; Schenetti, Luisa; Taddei, Ferdinando; L., Villa; V., Ferri
abstract

NMR spectra of a number of 2,4 disubstituted 1,3-dioxolanes have been recorded and analyzed. Vicinal coupling constants are found to be dependent on the substutuent at C-4 .

1980 - Structure and Protonation Study of the Imidazo[2.1-b]-1,3,4-thiadiazole System: 1H Nuclear Magnetic Resonance, Crystal and Molecular Structure of 5,6-Dimethylimidazo[2,1-b]-1,3,4-thiadiazole and its Hydrobrimide [Articolo su rivista]
Schenetti, Luisa; Taddei, Ferdinando; L., Greci; L., Marchetti; G., Milani; G., Andreetti; G., Bocelli; P., Sgarabotto
abstract

Crystalstructure analysis of 5,6-dimethylimidazo[2,1-b ]-1,3,4-thiadiazole (3) and its corresponding hydrobromide has shown that protonation occurs at N(7). Molecular properties, mainly aromaticity and basicity, of this system were interpreted on the basis of semi-empirically calculated ring-current, whic show that this molecules has a lower aromatic character than that of other fused heterocycles of imidazole with pyrimidine and thiazole rings. From 1-H nmr measurements the protonation site in acidic solution coul not be determined, but N(7) was found to be the site available for complex formation in the presence of a lanthanide shut reagent.

1979 - Conformational Behaviour of Organic carbonyl Compounds. Part 1. A Molecular Orbital Approach to the Study of Internal rotation in Conjugated Aldehydes and Ketones [Articolo su rivista]
Benassi, Rois; Schenetti, Luisa; Taddei, Ferdinando
abstract

Semi-empirical and ab-initio MO mrethods areemplojed in a srudy of internal rotation of conjugated aldehydes and ketones.

1975 - Structure and protonation study of the imidazo-{1,2-a]-pyrimidine system in 1H Nuclear Magnetic Resonance [Articolo su rivista]
L., Marchetti; L., Pentimalli; Lazzeretti, Paolo; Schenetti, Luisa; Taddei, Ferdinando
abstract

The 1H NMR spectra of imidazo [1,2-a]pyrimidine derivatives have been analysed to study the aromatic character and protonation behaviour of this system. By employing the ring currentn model and calculations based on the coupled Hartree-Fock method it can be deduced that a large -electron delocalisation exists in this heterocyclic system and affects the screening constant of the protons. Charge density schemes obtained by SCF techniques agree with the reactivity behaviour of these molecules.A detailed study of protonation carried out by following the 1H NMR spectra both in trifluoroacetic acid and in aqueous hydrochloric acid shows that the most probable site of protonation is N-1, but leaves open the possibility of a rapid exchange of one proton between N-1 and N-8.

1974 - 1H Nuclear Magnetic Resonance Study of para-Substituted Derivatives of Triphenylphosphine [Articolo su rivista]
Benassi, Rois; Schenetti, Luisa; Taddei, Ferdinando; Vivarelli, Piero; P., Dembech
abstract

1-H nmr investigation into para-substituted triarylphosphine derivatives is reported

1973 - 1H NMR Spectra of Oxiranes, cis-Arylmethyl Oxiranes Substituted in the Phenyl Ring, [Articolo su rivista]
L., Villa; Schenetti, Luisa; Taddei, Ferdinando
abstract

NMR spectra of title compounds

1972 - Diastereoisomeric Forms of alpha,alpha’-diphenyl-substituted Adiponitriles [Articolo su rivista]
G., Casini; M., Ferappi; B. R., Pietroni; Taddei, Ferdinando; Schenetti, Luisa
abstract

The preparation of some adiponitriles with two equivalent asymmetric carbon atoms in the alpha-alpha' positions is described. The two diastereoisomeric forms isolated for each of them are assigned meso and dl configurations on the basis of a detailed analysis of the NMR signals of the -CH2-CH2- groups, which constitute an AA'BB' spin-spin coupling system. The differences in physical properties of the meso and dl compounds are examined, and some partial and total hydrolysis reactions are described.

1972 - Nuclear Magnetic Resonance Spectroscopy of Tri-3-furylphosphine Derivatives [Articolo su rivista]
P., Dembech; G., Seconi; Vivarelli, Piero; Schenetti, Luisa; Taddei, Ferdinando
abstract

NMR spectra of tri-3-furylphosphine derivatives were examined and rationalize.

1971 - NMR Study of tautomerism in substituted 2-chlorobenzimidazioles [Articolo su rivista]
Benassi, Rois; Lazzeretti, Paolo; Schenetti, Luisa; Taddei, Ferdinando
abstract

Temperature dependence spectra were experimentally obtained and calculated, using the total line shape method.

1971 - Studies on Benzimidazoles . Part VIII. 1H Nuclear Magnetic Resonance Study of substituted 2-Chloro-1-methylbenzimidazoles, [Articolo su rivista]
P., Dembech; G., Seconi; P., Vivarelli; Schenetti, Luisa; Taddei, Ferdinando
abstract

A number of benzo-substituted 2-chloro-1-methylbenziimidazoles has been studied by 1-H NMR spectroscopy. It is observed both from the ring and N-methyl proton chemical shifys measured in CDCl3 and CF3COOH solution that conjugation effects are present between substituents and the nitrogen atoms of the heterocyclic ring. Proton-proton coupling constants can be rationalized in terms of additive substituent effects when there are no strong mesomeric interactions between substituents and the heterocyclic ring. Charge densities have been calculated for both sigma and pi-greek electrons, and the correlations between charges and chemical shifts show that the substituents also perturb the heterocyclic ring through the sigma skleton.