Conformational preferences of some substituted methyl groups in cyclohexanes as studied by carbon-13 nuclear magnetic resonance

✍ Scribed by William Kitching; Henry Olszowy; William Adcock

• Publisher: John Wiley and Sons
• Year: 1981
• Tongue: English
• Weight: 674 KB
• Volume: 15
• Category: Article
• ISSN: 0749-1581
• DOI: 10.1002/mrc.1270150304

✦ Synopsis

Low temperature l3c NMR spectra of 80: 20 mixtures of cis and trans-4-CH3-C6HloCHzX, where -CSHlOis 1,4-disubstituted cyclohexyl and X=Br, CN, OH, OCH,, Si(CH,),, Sn(CH3),, Pb(CH,), and HgOCOCH, have been recorded. The signals of the truns (e, e) components were assigned from the ambient temperature spectra of C6H,,CHZX and the established substituent effects of an equatorial methyl group in cyclohexane. Conformational equilibria of the cis (e, aFta, e) components were then computed from the intensities of the (remaining) signals (-180 K) of the two conformational isomers. From these equilibria A values of CHzX were calculated, assuming additivity of conformational energies of CH, and CHzX (the counter-poise approach). In general, these values are very similar to the value of CH,, although some trends do emerge.

This study provides a, p, y and S effects for a wide range of axial and equatorial -CH,X groups.