Electronic Structures and Conformations of N-Benzylideneanilines. I. Electronic Absorption Spectral Study Combined with CNDO/S CI Calculations

Abstract

The electronic structures and molecular conformations of N-benzylideneaniline and its several derivatives bearing 2-methyl, 2,6-dimethyl, and/or 4-nitro groups on the anilino benzene ring (ring A) have been investigated by electronic absorption spectroscopy combined with CNDO/S CI calculations. The lower energy bands are assigned and the molecular conformations are estimated. The results show that the 4-nitro derivatives as well as the 2,6-dimethyl derivatives take considerably twisted conformations.

cis–trans Isomerisation of Substituted Aromatic Imines: A Comparative Experimental and Theoretical Study

“…190 nm or 6.5 eV), with the first two merging into a double signal with the low-energy transition being the less intense one. In particular, the lowest-energy absorptions are in good agreement with experimental solution spectra, as reported in references [11] and [13]. In reference [13], for example, the two lowest absorption bands of NBA in cyclohexane were found at 315 (e = 7000), and 264 nm (17 000 L mol À1 cm…”

“…In contrast, trans-diazobenzenes are planar. To avoid imperfections caused by intermolecular forces in the crystalline state, studies in solution and in the gas phase by electronic absorption spectroscopy [12,13] and electron diffraction [14] were carried out, giving similar results. Different kinds of theoretical calculations also demonstrated the nonplanar conformation of trans-NBA derivatives.…”

“…[17,18] Later, different experimental methods, such as flash photolysis, [18][19][20] NMR spectroscopy, [21,22] UV/Vis spectroscopy [23] and IR spectroscopy, [24] were applied for further studies of this isomerisation process, including substituent [18-21, 23, 25] and solvent effects. [19,20,25] Moreover, for deeper analysis, semi-empirical [complete neglect of differential overlap (CNDO)] molecular orbital, [13,15] ab initio, [20] and density functional calculations [25,26] were performed. It was suggested that the photochemical trans!cis isomerisation was achieved by out-of-plane rotation around the C=N double bond, whereas thermal back relaxation proceeded by in-plane nitrogen inversion through a linear transition state (TS).…”

Ab initio DFT study of Z–E isomerization pathways of N–benzylideneaniline

“…In spite of this, the ultraviolet spectrum of NBA is remarkably different from the spectra of azobenzene and stilbene [6,7]. According to experimental [8,9] and theoretical studies [10][11][12] the main reason for this difference is the non-planar conformation of NBA, which is caused by the conjugation between the aniline ring and the nitrogen lone pair. This is in contrast to the nearly planar structure of the two other isoelectronic molecular systems.…”

An infrared study of the photoisomerization of N-benzylideneaniline

“…In addition to the above studies of the trans-cis isomerization, there have been others (10)(11)(12)(13)(14)(15)(16)(17), and references therein), both theoretical and experithe structure and conformation of Schiff bases. the structure and confrontation of Schiff bases.…”