Rotational isomerism about the Cα-CO bond in proline derivatives

Nagaraj, R. ; Venkatachalapathi, Y. V. ; Balaram, P. (1980) Rotational isomerism about the Cα-CO bond in proline derivatives International Journal of Peptide and Protein Research, 16 (4). pp. 291-298. ISSN 0367-8377

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The 270 MHz 1H n.m.r. spectrum of benzyloxycarbonyl-Pro-N-methylamide in CDCl3 is exchange broadened at 293° K. Spectral lines due to two species are frozen out at 253° K and a dynamically averaged spectrum is obtained at 323° K. A selective broadening of the Cβ and Cγ resonances in the 13C n.m.r. spectrum is observed at 253° K, with a splitting of the Cβ and Cγ resonances into a pair of lines of unequal intensity. A similar broadening of Cβ and Cγ peaks is also detected in pivaloyl-Pro-N-methylamide where cis-trans interconversion about the imide bond is precluded by the bulky t-butyl group. The rate process is thus attributed to rotation about the Cα-CO bond (ψ) and a barrier (ΔG#) of 14kcal mol-1 is estimated. 13C n.m.r. data for pivaloyl-Pro-N-methylamide in a number of solvents is presented and the differences in the Cβ and Cγ chemical shifts are interpreted in terms of rotational isomerism about the Cα-CO bond.

Item Type:Article
Source:Copyright of this article belongs to Munksgaard International Publishers.
Keywords:Activation Barriers; Nuclear Magnetic Resonance; Peptide Conformation; Proline; Rotational Isomerism
ID Code:4664
Deposited On:18 Oct 2010 07:10
Last Modified:16 May 2011 09:16

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