TY  - JOUR
A1  - Taddei, F.
A1  - Kleinpeter, Erich
T1  - The anomeric effect in substituted cyclohexanes : II. The role of hyperconjugative interactions and steric effect in 1,4-disubstituted cyclohexanes
N2  - The conformational equilibria of the cis/trans isomers of some 1,4-di-substituted cyclohexanes (X = OH, OMe, Me, OCOCH3, OCOC(CH3)(3), OCOCCl3, OCOCF3) were calculated at several levels of theory; the best correlation between calculated and experimentally available Delta G(0)s refers to the MP2/6-311 +G*//MP2/6-311G* results. In addition, the hyperconjugative effect of the substituents was studied with the NBO options included in the GAUSSIAN-98 package; a number of interactions between filled NBOs and antibonding orbitals could be considered as most representative for delocalization along the molecules studied. The effect of the substituents on the molecular geometry of the substituted cyclohexanesas well as the partitioning of both hyperconjugative and steric substituent effects on the present conformational equilibria is critically evaluated. Our model [E. Kleinpeter, F. Taddei, J. Mol. Struct. (THEOCHEM) 683 (2004) 29] for interpreting the relative stability of conformers of substituted cyclohexanes could be further verified and its reliability assessed. (c) 2005 Elsevier B.V. All rights reserved
Y1  - 2005
SN  - 0166-1280
ER  - 
TY  - JOUR
A1  - Taddei, F.
A1  - Kleinpeter, Erich
T1  - The anomeric effect in substituted cyclohexanes : I. The role of hyperconjugative interactions and steric effect in monosubstituted cyclohexanes
N2  - The relative energy of conformers, DeltaE, of monosubstituted cyclohexanes with OR (R = Me, Et, i-Pr and t-Bu) and R substituents (R = Me, Et, i-Pr and t-Bu) was calculated with MO ab initio theory at RHF, MP2 and QCISD levels with the 6-311G* and 6-311 + G* basis sets. A selected group of delocalizing interactions were calculated with the natural bond orbital method in order to quantify the hyperconjugative contribution, DeltaE(hyp.), to the relative stability of conformers. From the calculated values of DeltaE and DeltaE(hyp.) an estimate of the differential steric effect, DeltaE(ster.), of substituents in cyclohexane was obtained. The values of DeltaE(hyp), and DeltaE(ster.) show that they have a similar magnitude for OR substituents, while for R substituents the values of are greater. The shift in the conformational equilibrium towards the axial conformer, the so-called anomeric effect, takes place when, within a series of substituents, hyperconjugative interactions and steric interactions balance in favour of the stability of this conformer. (C) 2004 Elsevier B.V. All rights reserved
Y1  - 2004
SN  - 0166-1280
ER  - 
TY  - JOUR
A1  - Benassi, Rois
A1  - Bertarini, C.
A1  - Kleinpeter, Erich
A1  - Taddei, F.
T1  - Exocyclic push-pull conjugated compounds, Part 2 : the effect of donor and acceptor substituents on the rotational barrier of push-pull ethylenes
Y1  - 2000
ER  - 
TY  - JOUR
A1  - Benassi, Rois
A1  - Bertarini, C.
A1  - Kleinpeter, Erich
A1  - Taddei, F.
A1  - Thomas, Steffen
T1  - 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
Y1  - 2000
ER  - 
TY  - JOUR
A1  - Benassi, Rois
A1  - Bertarini, C.
A1  - Hilfert, Liane
A1  - Kempter, Gerhard
A1  - Kleinpeter, Erich
A1  - Spindler, Jürgen
A1  - Taddei, F.
A1  - Thomas, Steffen
T1  - Exocyclic push-pull conjugated compounds : Part 3
Y1  - 2000
ER  - 
TY  - JOUR
A1  - Benassi, Rois
A1  - Bregulla, Antje
A1  - Henning, Dietrich
A1  - Heydenreich, Matthias
A1  - Kempter, Gerhard
A1  - Kleinpeter, Erich
A1  - Taddei, F.
T1  - NMR-spectroscopic and theoretical structural analysis of 5-benzyl subtituted hydantoins in solutions
Y1  - 1999
ER  - 
TY  - JOUR
A1  - Benassi, Rois
A1  - Bregulla, Antje
A1  - Friedrich, Alwin
A1  - Henning, Dietrich
A1  - Heydenreich, Matthias
A1  - Mickler, Wulfhard
A1  - Kleinpeter, Erich
A1  - Kempter, Gerhard
A1  - Schilde, Uwe
A1  - Taddei, F.
T1  - NMR spectroscopic and theoretical structural study of 5-exo-methylene-substituted hydantoins
Y1  - 1998
ER  - 
TY  - JOUR
A1  - Kleinpeter, Erich
A1  - Heydenreich, Matthias
A1  - Kalder, L.
A1  - Koch, Andreas
A1  - Henning, Dietrich
A1  - Kempter, Gerhard
A1  - Benassi, Rois
A1  - Taddei, F.
T1  - NMR spectroscopic and theoretical structural analysis of 5,5-disubstituted hydantoins in solution
Y1  - 1997
ER  -