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Carbon-13 nuclear magnetic resonance spectroscopy. Substituent-induced chemical shift effects on cyclopropyl carbons of 4-substituted cyclopropylbenzenes

✍ Scribed by Yoshiaki Kusuyama; Christina Dyllick-Brenzinger; John D. Roberts

Publisher
John Wiley and Sons
Year
1980
Tongue
English
Weight
395 KB
Volume
13
Category
Article
ISSN
0749-1581

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✦ Synopsis

Abstract

Carbon‐13 chemical shifts of the cyclopropyl carbons of eleven 4‐substituted cyclopropylbenzenes have been measured under conditions effectively corresponding to infinite dilution in DCCI~3~. The substituent‐induced chemical shifts (SCS) of both the α and β carbons of the cyclopropane ring were found to be downfield with electron‐attracting groups and upfield for electron‐donating groups. The trends for the β carbons correspond to those observed for the β carbons of 4‐substituted phenylethenes, while the trends of the α carbons are similar to those found for the α carbons of 4‐substituted isopropyl benzenes. The results for the β carbons can be rationalized by postulating a substantial contribution from a hyperconjugative resonance effect involving the σ system of the benzene ring (and its 4‐substituent) and the C‐α—Cβ bonds of the cyclopropane ring. The effects on the α carbons are in accord with a very reasonable smaller inductive polarization of the C‐αC‐β bonds than encountered for the carbons of corresponding ethenyl‐ or ethynylbenzenes.

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