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Abnormal effect of hydroxyl on the longest wavelength maximum in ultraviolet absorption spectra for bis‐aryl Schiff bases
Author(s) -
Cao ChaoTun,
Zhou Wei,
Cao Chenzhong
Publication year - 2017
Publication title -
journal of physical organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.325
H-Index - 66
eISSN - 1099-1395
pISSN - 0894-3230
DOI - 10.1002/poc.3672
Subject(s) - chemistry , steric effects , schiff base , aryl , ultraviolet , spectral line , wavelength , absorption spectroscopy , absorption (acoustics) , crystallography , stereochemistry , optics , organic chemistry , alkyl , physics , astronomy
Two sets of bis‐aryl Schiff bases that contain 4(or 4′)‐OH and 2(or 2′)‐OH were synthesized. The first set consists of 4‐HOArCH=NArY and XArCH=NArOH‐4′, and the second set consists of 2‐HOArCH=NArY and XArCH=NArOH‐2′. Their ultraviolet absorption spectra were measured and investigated. A very interesting phenomenon was observed by analyzing their wave number ν max (cm −1 ) of longest wavelength maximum λ max (nm) of ultraviolet. Compared with the change regularity of the ν max of XArCH=NArY (where the X and Y excluded OH), the 4′‐position hydroxyl (4′‐OH) and 2′‐position hydroxyl (2′‐OH) have abnormal performance. The details are the following: the 4′‐OH contributes an additional red shift to the ν max of XArCH=NArOH‐4′ (λ max increase), whereas the 2′‐OH contributes an additional blue shift to the ν max of XArCH=NArOH‐2′ (λ max decrease). In addition, there are ortho steric effects of all 2‐OH and 2′‐OH on the ν max for 2‐HOArCH=NArY and XArCH=NArOH‐2′, and the ortho steric effect contributes a red shift to their ν max . These experimental facts can provide an important theoretical reference for us using aryl Schiff base compounds as optical materials and performing the molecular design.