ISSN:
0377-0486
Keywords:
Chemistry
;
Analytical Chemistry and Spectroscopy
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
,
Physics
Notes:
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 1H NMR or Raman spectroscopy. The Raman spectra of the isomers in CCl4 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 A1 type (with reference to the local symmetry C2ν of the cis-C—CH=CH—C group) consisting of the two C—H in-plane bendings and the C=C stretching, (2) a stronger band at 969 cm-1 ascribable to an A2-type coupled mode consisting of the two C—H out-of-plane waggings and the C=C torsion and (3) a unique band at 563 cm-1, tentatively related to an A-type coupled mode consisting of the C—C=C and C=C—C deformations. Methylated-cis configurations show a stronger Raman band around 880 cm-1 due to C—Me stretchings. Raman bands characteristic of each cis configuration (7-cis, 9-cis, 11-cis or 13-cis) also are discussed.
Additional Material:
6 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/jrs.1250150503
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