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Conformational studies of poly(cis-5-ethyl-D-proline)

✍ Scribed by Yang, Wayne W.-Y. ;Overberger, C. G. ;Venkatachalam, C. M.

Publisher
John Wiley and Sons
Year
1983
Weight
654 KB
Volume
21
Category
Article
ISSN
0360-6376

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✦ Synopsis

Abstract

Two possible conformations for poly(cis‐5‐ethyl‐D‐proline) have been identified and characterized by using combinations of ^1^H‐ and ^13^C‐NMR, CD, and ORD spectroscopic techniques. Both forms have helical conformations similar to those of poly(L‐proline) characterized by different amide bonds (cis and trans). However, the carbonyl group of the amide in poly(cis‐5‐ethyl‐D‐proline) form II (trans) seems to be closer to perpendicular orientation with respect to the helical axis than in poly(L‐proline) form II. The pyrrolidine ring conformation of form I (cis) is probably β^+^γ^−^‐puckered, whereas for form II it is probably β^+^‐puckered in nature. The side‐chain ethyl groups prefer to adopt anti conformations to the C~5~H bond, or prefer to have χ = 180°, regardless which of the two forms poly(cis‐5‐ethyl‐D‐proline) may like to assume. The experimental results agree well with our previous theoretical conformational energy calculations.

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