Axial asymmetry in the nuclear magnetic resonance spectra of deuterated methyl groups

An alternative explanation

Mieng Hua Wann, Gerard Harbison

Research output: Contribution to journalArticle

14 Citations (Scopus)

Abstract

The deuterium nuclear magnetic resonance (NMR) powder spectra of methyl groups at ambient temperatures are invariably averaged by rotation or hopping about the C3 axis. The canonical result for a perfectly threefold symmetric methyl is an axially symmetric Pake doublet whose splitting, in the case of perfect tetrahedral angles around the group, is averaged by a factor of exactly three. However, deuterium NMR spectra of methyl groups are often somewhat axially asymmetric, indicating a significant deviation either of the methyl group, or of its environment, from threefold symmetry. Previous explanations for this phenomenon have hinged on either an additional motional mechanism along a different axis, or on a perturbation of the field gradient around the methyl group by electronegative groups. We propose a simpler explanation; it may arise in a distortion of the methyl geometry itself, so that the group no longer has perfect rotational symmetry. We analyze some experimental examples of distorted methyls, and compare the extent of distortion required by the NMR data with those observed in published neutron structures.

Original languageEnglish (US)
Pages (from-to)231-237
Number of pages7
JournalThe Journal of Chemical Physics
Volume101
Issue number1
DOIs
StatePublished - Jan 1 1994

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Deuterium
Nuclear magnetic resonance
asymmetry
nuclear magnetic resonance
Powders
Neutrons
deuterium
Geometry
symmetry
ambient temperature
Temperature
deviation
neutrons
perturbation
gradients
geometry

ASJC Scopus subject areas

  • Physics and Astronomy(all)
  • Physical and Theoretical Chemistry

Cite this

Axial asymmetry in the nuclear magnetic resonance spectra of deuterated methyl groups : An alternative explanation. / Wann, Mieng Hua; Harbison, Gerard.

In: The Journal of Chemical Physics, Vol. 101, No. 1, 01.01.1994, p. 231-237.

Research output: Contribution to journalArticle

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