Collect. Czech. Chem. Commun.
1983, 48, 3086-3096
https://doi.org/10.1135/cccc19833086
Electrostatic effects on conformational equilibria: Alkyl 2-cyanobenzoates and 3-cyanopropenoates
Otto Exnera, Zdeněk Friedlb and Pavel Fiedlera
a Institute of Organic Chemistry and Biochemistry, Czechoslovak Academy of Sciences, 166 10 Prague 6
b Department of Organic Chemistry, Slovak Institute of Technology, 880 37 Bratislava
Abstract
The conformational equilibrium ap ⇌ sp of the title compounds was investigated by two methods: dipole moment measurement in benzene solution and IR spectroscopy of the carbonyl band in decahydronaphthalene solution. Approximately 71% of the ap rotamers were found for 2-cyanobenzoates (II, III), and between 60 to 80% for (Z)-3-cyanopropenoates (V, VI). This result does not reveal any special attractive interaction between the carbonyl oxygen and cyano carbon atoms; on the other hand, it is in fair agreement with electrostatic calculations based on point charges calculated from bond moments. Any attractive interaction was not detected even on aliphatic cyano esters VII-IX. Comparison of several model compounds and several kinds of approximative calculations leads us to conclude that the electrostatic model works generally better for conformational equilibria than for ionization equilibria.
