Conformational studies by dynamic NMR. V. The stereodynamics of hindered aliphatic hydrazones

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DOIResolve DOI: http://doi.org/10.1021/ja00440a005
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TypeArticle
Journal titleJournal of the American Chemical Society
ISSN0002-7863
Volume98
Issue24
Pages74847488; # of pages: 5
AbstractA number of N-ketiminyl-2,2,6,6-tetramethylpiperidines (TMP-N=CR2) have been synthesized and investigated by 1H NMR spectroscopy. The piperidyl methyls are either nonequivalent in pairs at room temperature or become nonequivalent in pairs at low temperatures. This is shown to be due to restricted rotation about the N-N bond, a phenomenon that is not observed in less hindered hydrazones even at very low temperatures. The free energies of activation for rotation in TMP-N=CR2 were determined by line shape analysis. They increase from a low of 7.6 kcal/mol for R2 = H2 through 11.6, 14.35, and 18.0 kcal/mol for R2 = (CH2)4, (CH2)5, and (CH2)6, respectively. This trend is rationalized in terms of a conformation in which the plane of the N=CR2 moiety is perpendicular to the dynamically averaged plane of the tetramethylpiperidine ring. This conclusion is supported by an x-ray diffraction determination of the structure and conformation of TMP-N=C-(CH3)C6H5. The rotational barriers of some n-nitrosoamines are also reported.
Publication date
LanguageEnglish
AffiliationNational Research Council Canada (NRC-CNRC)
Peer reviewedYes
NPARC number21276650
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Record identifierc4db8d54-7aa9-4c61-ae21-d25f9a8bf0dd
Record created2015-10-13
Record modified2016-05-09
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