Conformational analysis and stereodynamics of primary acyclic alkyl radicals by EPR spectroscopy

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DOIResolve DOI: http://doi.org/10.1021/j100404a017
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TypeArticle
Journal titleThe Journal of Physical Chemistry
ISSN0022-3654
Volume90
Issue13
Pages28592869; # of pages: 11
AbstractThe EPR spectra of n-alkyl, 2-methylalkyl, 2,2-dimethylalkyl, 2,2,3-trimethylbutyl, and 2,2,3,3-tetramethylbutyl radicals indicate that at 90 K they exist in "rigid" conformations with respect to rotation about the Cβ-Cγ bonds. The preferred conformations about the Cα-Cβ and Cβ-Cγ bonds were deduced by analysis of the β- and γ-H hyperfine splittings (hfs). 2,2,3,3-Tetramethylbutyl radicals, the only radicals with a CH3 group approximately all-trans with respect to the semioecupied p-orbital, were also the only radicals to show resolved δ-hfs. The barriers to internal rotation of the methyl groups in n-propyl, isobutyl, neopentyl, 2,2-bis(trideuteriomethyl)butyl, and 2,2,3,3-tetramethylbutyl radicals were obtained by line shape analysis; the ethyl rotation barrier in 2,2-bis(trideuteriomethyl)butyl and the tert-butyl rotation barrier in 2,2,3,3-tetramethylbutyl radicals were estimated in a similar way. The experimental hfs of trans γ-hydrogens were shown to fit a relationship of the form aHγt = 0.1 + 7.9 cos2 Φ, where Φ is the dihedral angle between the SOMO and the plane through Cα, Cβ, and Cγ. Trends in the internal rotation barriers of the alkyl groups were adequately accounted for in terms of steric effects.
Publication date
LanguageEnglish
AffiliationNational Research Council Canada (NRC-CNRC)
Peer reviewedYes
NPARC number21276486
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Record identifier31567b81-0fff-4fe9-9f56-69d4422a9762
Record created2015-10-13
Record modified2017-03-23
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