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Title: Conformational studies of selectively methylated [2.2](1,3)(1,4)cyclophanes. Steric effects in the relative conformational ground states
Authors: Lai, Y.-H. 
Yap, A.H.-T.
Novak, I. 
Issue Date: 1994
Citation: Lai, Y.-H.,Yap, A.H.-T.,Novak, I. (1994). Conformational studies of selectively methylated [2.2](1,3)(1,4)cyclophanes. Steric effects in the relative conformational ground states. Journal of Organic Chemistry 59 (12) : 3381-3385. ScholarBank@NUS Repository.
Abstract: Three selectively methylated [2.2](1,3)(1,4)cyclophanes, namely, 12,15-dimethyl-, 12,16-dimethyl-, and 12,13,14,15-tetramethyl[2.2](1,3)(1,4)cyclophanes, were synthesized from their corresponding dithia[3.3](1,3)(1,4)cyclophanes by the photochemical desulfurization method. Dynamic 1H NMR spectroscopy was employed to estimate the relative conformational barrier in each [2.2]cyclophane. The results show that there is an increase of about 13 kJ mol-1 going from the parent [2.2](1,3)-(1,4)cyclophane to its 12,15- and 12,16-dimethyl derivatives. This is consistent with the fact that the presence of the methyl substituents increases the relative conformational ground-state energy more than it would affect the transition-state energy. The conformational barrier of the 12,13,-15,16-tetramethyl derivative was unexpectedly found to be similar to those of the two dimethylated derivatives. This however could be explained by a decrease in the transition-state energy due to inward bending of the (1,4)-bridged ring accompanied by a decrease in conformational ground-state energy due to outward bending of the methyl groups. © 1994 American Chemical Society.
Source Title: Journal of Organic Chemistry
ISSN: 00223263
Appears in Collections:Staff Publications

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