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17O NMR study of p-π conjugation in methoxybutadienes and related compounds

✍ Scribed by Esko Taskinen

Publisher
John Wiley and Sons
Year
1995
Tongue
English
Weight
367 KB
Volume
33
Category
Article
ISSN
0749-1581

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✦ Synopsis

The '"0 NMR spectra of some monomethoxy and dimethoxy derivatives of buta-l,Miene, hexa-2,4-diene, cyclohexa-1,fdiene and cyclohexa-l,44iene were recorded in CDCl,. The "'0) values show that in 2methoxybuta-1,fdiene the efficiency of p-n conjugation in the -0-C-C moeity is significantly lowered by crossconjugation of the C-C bond with the other olefinic linkage. In the related system of 2-methoxycyclohexa-1,3diene, however, the corresponding effect is much smaller, apparently because of weak conjugative 7r-z interaction in the olefinic system. On the other hand, the strength of pn conjugation appears to be the same in the -0-C=C-C=C moieties of both l-methoxybuta-1,Miene and l-methoxycyclohexa-1,Miene. Moreover, as a transmitter of substituent effects, the unsaturated system of cyclohexa-l,3diene is comparable to that of the benzene nucleus.

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