title: Effects of single bond-ion and single bond-diradical form on the stretching vibration of C=N bridging bond in 4,4'-disubstituted benzylidene anilines.
abstract: Fifty-seven samples of model compounds, 4,4'-disubstituted benzylidene anilines, p-X-ArCH=NAr-p-Y were synthesized. Their infrared absorption spectra were recorded, and the stretching vibration frequencies νC=N of the C=N bridging bond were determined. New stretching vibration mode was proposed by means of the analysis of the factors affecting νC=N, that is there are mainly three modes in the stretching vibration of C=N bond: (I) polar double bond form C=N, (II) single bond-ion form C(+)-N(-) and (III) single bond-diradical form C-N. The contributions of the forms (I) and (II) to the change of νC=N can be quantified by using Hammett substituent constant (including substituent cross-interaction effects between X and Y groups), whereas the contribution of the form (III) can be quantified by employing the excited-state substituent constant. The most contribution of these three forms is the form (III), the next is the form (II), whose contribution difference was discussed with the viewpoint of energy requirements in vibration with the form (III) and form (II).
authors.affiliation: School of Chemistry and Chemical Engineering, Hunan University of Science and Technology, Xiangtan 411201, China; Key Laboratory of Theoretical Organic Chemistry and Function Molecule, Hunan University of Science and Technology, Xiangtan 411201, China; Ministry of Education, Hunan Provincial University Key Laboratory of QSAR/QSPR, Xiangtan 411201, China.
authors.forename: Chao-Tun
authors.initials: CT
authors.lastname: Cao
authors.affiliation: School of Chemistry and Chemical Engineering, Hunan University of Science and Technology, Xiangtan 411201, China; Key Laboratory of Theoretical Organic Chemistry and Function Molecule, Hunan University of Science and Technology, Xiangtan 411201, China; Ministry of Education, Hunan Provincial University Key Laboratory of QSAR/QSPR, Xiangtan 411201, China.
authors.forename: Yakun
authors.initials: Y
authors.lastname: Bi
authors.affiliation: School of Chemistry and Chemical Engineering, Hunan University of Science and Technology, Xiangtan 411201, China; Key Laboratory of Theoretical Organic Chemistry and Function Molecule, Hunan University of Science and Technology, Xiangtan 411201, China; Ministry of Education, Hunan Provincial University Key Laboratory of QSAR/QSPR, Xiangtan 411201, China. Electronic address: czcao@hnust.edu.cn.
authors.forename: Chenzhong
authors.initials: C
authors.lastname: Cao
keywords: Benzylidene aniline; Infrared absorption spectrum; Single bond-diradical form; Single bond-ion form; Stretching vibration of CN bond