Laboratory for Computational Molecular Design, Institut des Sciences et Ingénierie Chimiques, Ecole Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland.
J Phys Chem A. 2010 Jun 24;114(24):6705-12. doi: 10.1021/jp1029322.
The ring strain energies of carbomeric-cycloalkanes (molecules with one or more acetylene spacer units placed into carbon single bonds) are assessed using a series of isodesmic, homodesmotic, and hyperhomodesmotic chemical equations. Isodesmic bond separation reactions and other equations derived from the explicitly defined hierarchy of homodesmotic equations are insufficient for accurately determining these values, since not all perturbing effects (i.e., conjugation and hyperconjugation) are fully balanced. A set of homodesmotic reactions is proposed, which succeeds in balancing all stereoelectronic effects present within the carbomeric rings, allowing for a direct assessment of the strain energies. Values calculated from chemical equations are validated using an increment/additivity approach. The ring strain energy decreases as acetylene units are added, manifesting from the net stabilization gained by opening the C-CH(2)-C angle around the methylene groups and the destabilization arising from bending the C-C identical withC angles of the spacer groups. This destabilization vanishes with increasing parent ring size (i.e., the angle distortion is less in the carbomeric-cyclobutanes than in the carbomeric-cyclopropanes), leading to strain energies near zero for carbo(n)-cyclopentanes and carbo(n)-cyclohexanes.
使用一系列等电子、同电子和超同电子化学方程来评估碳杂环烷烃（在碳单键中放置一个或多个乙炔间隔单元的分子）的环应变能。等电子键分离反应和其他源自同电子方程明确定义的层次结构的方程不足以准确确定这些值，因为并非所有的扰动效应（即共轭和超共轭）都能完全平衡。提出了一组同电子反应，它们成功地平衡了碳杂环中存在的所有立体电子效应，从而可以直接评估应变能。使用增量/加性方法验证从化学方程计算的值。随着乙炔单元的添加，环应变能降低，这是由于在亚甲基周围打开 C-CH(2)-C 角而获得的净稳定化，以及由于弯曲间隔基团的 C-C 相同的 C 角而导致的失稳。随着母体环尺寸的增加，这种失稳消失（即，在碳杂环丁烷中角变形小于在碳杂环丙烷中），导致碳（n）-环戊烷和碳（n）-环己烷的应变能接近零。
