Substituent effects in chain and ring π-systems studied by core-electron binding energies calculated by density functional theory

The substituent effects of X- in 1-X-hexatrienes, which are chain pi-systems with conjugated double bonds, was compared with those in Ph-X, which are ring pi-systems, using core electron binding energy shifts (Delta CEBE) of the carbon atoms in the molecules. The Delta CEBE of C-1-C-4 in 1-X-hexatrienes are generally close to Delta CEBE of C-1-C-4 in Ph-X. The Delta CEBE of carbon atoms in the 1-X-hexatrienes are not only highly correlated to the Hammett sigma substituent constants, but their numerical values are also close to each other. The core electron binding energies (CEBE) of the six carbons in 1-X-hexatriynes, which are the chain pi-systems with conjugated triple bonds, were calculated by density functional theory (DFT) and the substituent effect was investigated. Average Delta CEBE of the five carbon atoms between C-2 and C-6 in 1-X-hexatriyne were calculated. The magnitude and sign of the average Delta CEBE provides quantitative strength and direction, electron withdrawing or donating, of a substituent X. (C) 2011 Published by Elsevier B.V.