Natural bond orbital approach to the transmission of substituent effect through the fulvene and benzene ring systems

Abstract

Electronic structure of 22 monosubstituted derivatives of benzene and exocyclically substituted fulvene with substituents: B(OH)(2), BH(2), CCH, CF(3), CH(3), CHCH(2), CHO, Cl, CMe(3), CN, COCH(3), CONH(2), COOH, F, NH(2), NMe(2), NO, NO(2), OCH(3), OH, SiH(3), SiMe(3) were studied theoretically by means of Natural Bond Orbital analysis. It is shown, that sum of π-electron population of carbon atoms of the fulvene and benzene rings, pEDA(F) and pEDA(B), respectively correlate well with Hammett substituent constants [Formula in text] and aromaticity index NICS. The substituent effect acting on pi-electron occupation at carbon atoms of the fulvene ring is significantly stronger than in the case of benzene. Electron occupations of ring carbon atoms (except C1) in fulvene plotted against each other give linear regressions with high correlation coefficients. The same is true for ortho- and para-carbon atoms in benzene. Positive slopes of the regressions indicate similar for fulvene and benzene kind of substituent effect - mostly resonance in nature. Only the regressions of occupation at the carbon atom in meta- position of benzene against ortho- and para-positions gives negative slopes and low correlation coefficients.

Electronic properties and aromaticity of substituted diphenylfulvenes in the ground (S0) and excited (T1) states

“…Previously, the correlation of the number of π electrons in the monosubstituted fulvenes with σ p + Hammett constants and aromaticity index NICS were investigated [13], in addition to the correlations of a few magnetic indices of aromaticity with ASE and HOMA for disubstituted fulvenes [14]. However, the correlations had been studied only for the molecules in the ground electronic state.…”

“…Fulvene has been shown by spectroscopic methods to be a planar, non-aromatic molecule of C 2v symmetry with C-C bonds that alternate in length, consistent with localized single and double bonds [1,2]. The fulvene properties, as well as properties of its derivatives (fulvenes), have been the subject of numerous experimental [2][3][4][5] and theoretical investigations [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21]. Further, the methods for generation of fulvenes and their rich cycloaddition chemistry have been recently reviewed [3].…”

“…Further, the methods for generation of fulvenes and their rich cycloaddition chemistry have been recently reviewed [3]. The properties of fulvenes studied by theoretical methods have included the aromaticity and electronic structures [5,[7][8][9][10][12][13][14][15][16][17][18][19]. It has been found that electron-donating substituents attached to the exocyclic carbon in fulvenes significantly increase their aromatic character [5,7,13,14].…”

Predicting reduction potentials of 1,3,6‐triphenyl fulvenes using molecular electrostatic potential analysis of substituent effects

“…In the case of fulvenes, a study suggested that the lowest electronic states of fulvene can be varied with substituents . Oziminski and Krygowsky interposed a correlation between π‐electron population at carbon atoms of the ring in fulvene and benzene with substituent constant and with aromaticity index NICS …”

“…[12] Oziminski and Krygowsky interposed a correlation between p-electron population at carbon atoms of the ring in fulvene and benzene with substituent constant and with aromaticity index NICS. [38] Molecular electrostatic potential (MESP) has been widely accepted as an electronic descriptor in predicting reactivities. [39][40][41][42] Gadre and Suresh employed MESP to study the electronic perturbations due to substituent effects.…”