Abstract
A series of N-alkyl and N-alkyl-aryl free radicals with the structure ▪ was synthesized and the samples were investigated by ESR spectroscopy. The restricted rotation of the N-alkyl group is characterized by the deviation of the β hydrogen coupling constant of the N-alkyl group from that of the freely rotating N-methyl group: R = a H β/a H CH 3 . Correlations were found between the R restriction parameter and the geometric size of the X,Y and Z groups. For methine group CHYZ the R parameter was found to decrease with the size of the X group and increase with the relative magnitude of Y group compared to Z. If X is a phenyl group, its ortho substitution exerts an orienting effect on the N-alkyl group. For the methylene group CH 2Y the R factor decreases with the size of the Y group. The trends observed were applied to examine the validity of the different theoretical models described in the literature in interpreting the restricted rotation of N-alkyl groups.
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