Substituent Effects in Cross-Conjugated Systems

Substituent effects in cross-conjugated systems were carried out on a series of substituted 3-methylenepenta- 1,4-diynes with primary carbocation CH2+. Their optimized energies were calculated at the B3LYP/6-31G (d) level. The substituent effects were expressed in terms of isodesmic reactions and were analyzed by LSFE equation. The analysis results show that the substituent effect is inversely proportional to the stability of the whole molecule. In other words, the more stable the cross-conjugated molecule is, the smaller it's substituent effect become.