title: Routes of π-electron delocalization in 4-substituted-1,2-benzoquinones.
abstract: The substituent effect in 4-substituted-1,2-benzoquinone is investigated by means of modeling using B3LYP hybrid functional in conjunction with the 6-311+G(d,p) basis set. The interrelation between different types of substituents, X = NO, NO(2), CN, CHO, H, Me, OMe, OH, NH(2), NHMe and N(Me)(2), and both CO groups has been characterized both qualitatively and then quantitatively by means of several measures of π-electron delocalization (HOMA, MCI, DI, FLU) based on structural and electronic properties of 4-substituted-1,2-benzoquinones chosen for analysis. Results of this analysis clearly show that only the meta-placed CO group is affected by substituents, whereas the para-placed CO group is rather insensitive to substitution. These observations may help to explain diversified chemical properties (including reactivity) of CO centers in o-benzoquinone derivatives. Among others, they may explain differences in proton-accepting properties of carbonyl O atoms, as it is shown for simple models in which carbonyl groups in o-benzoquinone act as proton acceptors in H-bonds of O···H-F type.
authors.affiliation: Faculty of Chemistry, Warsaw University of Technology, Noakowskiego 3, 00-664 Warsaw, Poland. halina@ch.pw.edu.pl
authors.forename: Halina
authors.initials: H
authors.lastname: Szatyłowicz
authors.forename: Tadeusz M
authors.initials: TM
authors.lastname: Krygowski
authors.forename: Marcin
authors.initials: M
authors.lastname: Palusiak
authors.forename: Jordi
authors.initials: J
authors.lastname: Poater
authors.forename: Miquel
authors.initials: M
authors.lastname: Solà