TY  - JOUR
A1  - Kleinpeter, Erich
A1  - Klod, Sabrina
A1  - Rudorf, Wolf-Dieter
T1  - Electronic state of push-pull alkenes : an experimental dynamic NMR and theoretical ab initio MO study
N2  - The H-1 and C-13 NMR spectra of a number of push-pull alkenes were recorded and the C-13 chemical shifts calculated employing the GIAO perturbation method. Of the various levels of theory tried, MP2 calculations with a triple- zeta-valence basis set were found to be the most effective for providing reliable results. The effect of the solvent was also considered but only by single-point calculations. Generally, the agreement between the experimental and theoretically calculated C-13 chemical shifts was good with only the carbons of the carbonyl, thiocarbonyl, and cyano groups deviating significantly. The substituents on the different sides of the central C=C partial double bond were classified qualitatively with respect to their donor (S,S < S,N < N,N) and acceptor properties (CdropN < C=O < C=S) and according to the ring size on the donor side (6 < 7 < 5). The geometries of both the ground (GS) and transition states (TS) of the restricted rotation about the central C=C partial double bond were also calculated at the HF and MP2 levels of theory and the free energy differences compared with the barriers to rotation determined experimentally by dynamic NMR spectroscopy. Structural differences between the various push-pull alkenes were reproduced well, but the barriers to rotation were generally overestimated theoretically. Nevertheless, by correlating the barriers to rotation and the length of the central C=C partial double bonds, the push-pull alkenes could be classified with respect to the amount of hydrogen bonding present, the extent of donor-acceptor interactions (the push-pull effect), and the level of steric hindrance within the molecules. Finally, by means of NBO analysis of a set of model push-pull alkenes (acceptors: - CdropN, -CH=O, and -CH=S; donors: S, O, and NH), the occupation numbers of the bonding pi orbitals of the central C=C partial double bond were shown to quantitatively describe the acceptor powers of the substituents and the corresponding occupation numbers of the antibonding pi* orbital the donor powers of the substituents. Thus, for the first time an estimation of both the acceptor and the donor properties of the substituents attached to the push-pull double bond have been separately quantified. Furthermore, both the balance between strong donor/weak acceptor substituents (and vice versa) and the additional influences on the barriers to rotation (hydrogen bonding and steric hindrance in the GSs and TSs) could be differentiated
Y1  - 2004
ER  - 
TY  - JOUR
A1  - Kleinpeter, Erich
A1  - Koch, Andreas
A1  - Heydenreich, Matthias
A1  - Chatterjee, S. K.
A1  - Rudorf, Wolf-Dieter
T1  - Study of the pi-electron distribution in push-pull alkenes by 1H and 13C NMR spectroscopy, IV : the conformation and dynamic behaviour of substituted N-Phenyl-2,3-dihydro-4(1H)-pyridones
Y1  - 1995
ER  - 
TY  - JOUR
A1  - Kleinpeter, Erich
A1  - Heydenreich, Matthias
A1  - Chatterjee, S. K.
A1  - Rudorf, Wolf-Dieter
T1  - Study of the pi-electron distribution in push-pull alkenes by 1H and 13C NMR spectroscopy, III : the conformation of 3,4-Dihydro-4-oxo-2H-thiins
Y1  - 1994
ER  - 
TY  - JOUR
A1  - Kleinpeter, Erich
A1  - Heydenreich, Matthias
A1  - Chatterjee, S. K.
A1  - Rudorf, Wolf-Dieter
T1  - Study of the pi-electron distribution in push-pull alkenes by 1H and 13C NMR spectroscopy
Y1  - 1994
ER  - 
TY  - JOUR
A1  - Kleinpeter, Erich
A1  - Thomas, Steffen
A1  - Uhlig, G.
A1  - Rudorf, Wolf-Dieter
T1  - Study of the distribution of pi-Electrons in Push-Pull Alkenes by 1H an 13C NMR spectroscopy
Y1  - 1993
ER  -