ACYCLIC VERSUS CYCLIC pi-ELECTRON DELOCALIZATION.HOW IS THE SUBSTITUENT EFFECT RELATED TO pi-ELECTRON DELOCALIZATION?

摘要

Substituent effect stabilization energies were estimated for sets of 27 para-substituted phenol derivatives,meta-and para-homodisubstituted benzene derivatives,trans-substituted ethenes,4-substituted 1-hydroxgamma-1,3-cyclohexadienes and 1,4-homodisubstituted 1,3-cyclohexadienes based on the optimizations at the B3LYP/6-311+G** DFT level of theory.The following sub-stituents were taken into account:C ident to CH,C(CN)3,CF3,CH2NH2,CH3,CH=CH2,CHO,Cl,CN,COCH3,COCl,CONH2,COOCH3,COOH,F,NH2,NHCH3,N(CH3)2,NHOH,NO,NO2,OCH3,OH,Ph,H,SH,SO2CN.For hydroxyethenes and phenol derivatives the electron-acceptor substituents stabilize the systems,whereas the electron-donors lead to their destabilization.Both electron-acceptor and electron-donor substituents destabilize homodisubstituted ethene and meta-and para-homodisubstituted benzene species.The strongest destabilization is observed for derivatives of ethene,a weaker one for derivatives of cyclohexadiene and the weakest for benzene derivatives.