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Raman and infrared spectra of the 7‐ cis and di‐ cis isomers of retinal
Author(s) -
Koyama Yasushi,
Mukal Yumiko,
Umemura Junzo,
Ito Masayoshi,
Tsukida Kiyoshi
Publication year - 1984
Publication title -
journal of raman spectroscopy
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.748
H-Index - 110
eISSN - 1097-4555
pISSN - 0377-0486
DOI - 10.1002/jrs.1250150503
Subject(s) - raman spectroscopy , cis–trans isomerism , chemistry , infrared , spectral line , photoisomerization , infrared spectroscopy , analytical chemistry (journal) , isomerization , crystallography , stereochemistry , organic chemistry , optics , physics , catalysis , astronomy
The Raman and infrared spectra of the 7‐ cis , 9‐ cis , 11‐ cis , 9‐ cis , 13‐ cis and 11‐ cis , 13‐ cis isomers of retinal have been recorded for the first time. The spectra of the all‐ trans , 9‐ cis , 11‐ cis and 13‐ cis isomers were also recorded for comparison. The isomers were isolated from a photoisomerization mixture of the all‐ trans isomer and their configurations were identified by means of 1 H NMR or Raman spectroscopy. The Raman spectra of the isomers in CCl 4 solution were recorded using a flow method, the 457.9 nm line of an Ar + laser and a Raman spectrometer equipped with a multichannel detector; their infrared spectra were recorded by using an FT‐IR spectrophotometer. Comparison of the Raman spectra of the mono‐ cis isomers revealed key bands which, discriminate between unmethylated‐ cis (7‐ cis and 11‐ cis ) and methylated‐ cis (9‐ cis and 13‐ cis ) configurations. The key bands were related to local vibrations around the particular cis double bond. Unmethylated‐ cis configurations show (1) a unique band around 1280‐1270 cm −1 due to a coupled mode of A 1 type (with reference to the local symmetry C 2ν of the cis ‐CCHCHC group) consisting of the two CH in‐plane bendings and the CC stretching, (2) a stronger band at 969 cm −1 ascribable to an A 2 ‐type coupled mode consisting of the two CH out‐of‐plane waggings and the CC torsion and (3) a unique band at 563 cm −1 , tentatively related to an A ‐type coupled mode consisting of the CCC and CCC deformations. Methylated‐ cis configurations show a stronger Raman band around 880 cm −1 due to CMe stretchings. Raman bands characteristic of each cis configuration (7‐ cis , 9‐ cis , 11‐ cis or 13‐ cis ) also are discussed.