Author:
Johnson LF,Robertson AV,Simpson WRJ,Witkop B
Abstract
Slight changes in the chemical shifts of
protons in 3,4-dehydroproline derivatives cause the appearance of their proton
magnetic resonance spectra to change markedly, and this can be effected by
taking one compound in two different solvents or by observing closely related
derivatives in the same solvent. The explanation involves a previously
undescribed type of deceptively simple coupling and the necessary conditions
are discussed. A first-order analysis of the ABMXX' pattern for
3,4-dehydroprolinamide in deuterium oxide is given. A full analysis is made of
the ABXX' and ABXY patterns for this amide in deuterium oxide and deuterochloroform
respectively after deuterium exchange of the labile H2; a very large homoallylic coupling is required. Two conformations exist
at 40� in solution for all N-benzyloxycarbonyl methyl esters of proline and its
derivatives due to restricted rotation about the amide bond. Free rotation of
the amide bond of corresponding N-acetyl and AT-benzoyl derivatives still
occurs at -50�. The deceptively simple spectrum of N-benzyloxycarbonyl-2,5-dihydroxy-Δ3-pyrolne
is discussed and that of its diacetate is analysed as an A2X2
system; a very small homoallylic coupling is
required.
Cited by
26 articles.
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