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Assignment of the configuration of a substituent in saturated six-membered ring compounds using the 13C chemical shifts of a single epimer

✍ Scribed by K. Pandiarajan; A. Manimekalai

Publisher: John Wiley and Sons
Year: 1993
Tongue: English
Weight: 738 KB
Volume: 31
Category: Article
ISSN: 0749-1581
DOI: 10.1002/mrc.1260310117

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✦ Synopsis

Abstract

The possibility of assigning the configuration of a substituent in six‐membered ring compounds from the ^13^C chemical shifts of a single epimer was examined. The chemical shifts of the ring carbons in saturated six‐membered ring compounds were calculated using standard substituent parameters obtained from tert‐butyl systems, and these calculated values were compared with the observed values. It was found that in isomeric 1,3‐ and 1,4‐disubstituted cyclohexanes the configuration could be assigned correctly for each isomer by comparing the observed chemical shifts with the calculated values, an exception being trans‐1,3‐dihydroxycyclohexane. However, in the 1,2‐disubstituted cyclohexanes the configuration could be assigned correctly only by comparing the observed and calculated chemical shifts for the γ‐ or β‐methylene carbons. The configuration cannot be assigned correctly in heterocyclic systems by using the individual chemical shifts as probes. However, when the sum of the chemical shifts of the ring carbons could be calculated for equatorial and axial orientations of the substituent using standard substituent parameters to a reasonable degree of accuracy, the configuration for any epimer could be assigned correctly by comparing the observed and calculated sums.

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