Site-specific isotope labeling demonstrates a large mesomeric resonance effect of the methoxy groups on the carbonyl frequency in ubiquinones

The splitting of the carbonyl infrared bands of 2-methoxy-1,4-benzoquinone in solution can be related to a mesomeric resonance phenomenon leading to a conformation of the O-CH^sub 3^ bond coplanar to the quinone ring. The delocalization of the electron density induces a frequency downshift of the C^...

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Bibliographic Details
Published in:Photosynthesis research 1998-03, Vol.55 (2/3), p.247-252
Main Authors: Boullais, C, Nabedryk, E, Burie, J.R, Nonella, M, Mioskowski, C, Breton, J
Format: Article
Language:English
Subjects:
Carbon
chemical structure
isotope labeling
oscillation
photosynthesis
resonance
ubiquinones
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Summary:The splitting of the carbonyl infrared bands of 2-methoxy-1,4-benzoquinone in solution can be related to a mesomeric resonance phenomenon leading to a conformation of the O-CH^sub 3^ bond coplanar to the quinone ring. The delocalization of the electron density induces a frequency downshift of the C^sub 4^=O carbonyl compared to 1,4-benzoquinone. This in turns decouples the two carbonyls leading to an upshift of the C^sub 1^=O vibration. Using selective ^sup 13^C-labeling of Q^sub 0^ (2,3-dimethoxy-5-methyl-1,4-benzoquinone), we show that the effect of mesomeric resonance is an essential determinant of the carbonyl frequencies of ubiquinone in solution.[PUBLICATION ABSTRACT]
ISSN:0166-8595
1573-5079
DOI:10.1023/a:1005979817422