The barrier to rotation about the a mido C-N bond has been measured for five C-substituted N, 'dime thylamides. Dimethylcarbamyl chloride has been extensively studied previously, and a critical survey of the systematic errors in all determinations has been achieved by a composite plot of the derived parameters A6f* vs. AS *.

Dioxane is at least 90 and probably over 98% nonpolar conformer, but is best viewed as a fluxional molecule with frequency of maximum conversion between conformers somewhat above 5 cm-1 (1.5 X 1011 Hz).(5) The ternary system here may be used as a solvent system having variable amounts of electron cloud character, but not for varying amounts of local electric field.Acknowledgments. This note includes work submitted to Middlebury College, Middlebury, VT, in partial fulfillment of the requirements for the degrees of Bachelor of Arts for . M. and of Master of Science for J. X. S. The work was supported by Grant No.

Hindered rotation (HR) about the N-C amido bond in samples of 3-dimethylaminoacrylonitrile and (dimethylaminoethylene)malonitrile has been examined by proton magnetic resonance. Substitution of the =CH2 moeity in place of chalcogens in the amide structure leads to a large decrease in the barrier to rotation about the amido N-C bond, but substitution of electronegative groups for hydrogen in =CH2 then causes an increase in the barrier. The effects of CN substitution are manifest by stabilization of the carbanion resonance structure. In turn, the free energy of activation for HR is found to increase approximately with the square of the total mesomeric interacting potential of the substituents. Eight-site formulation of the chemical exchange for 3-dimethylaminoacrylonitrile requires consideration of parity in the signs of long-range couplings. Thus it is suggested that both of the 4J(CH3-H) and ®J(CH3~H) couplings have the same sign. This is substantiated by line shape analysis and the magnitudes of the averaged couplings in the fast exchange limit. The magnitudes of all couplings are reported and they are considered to be dependent upon the extent of tt conjugation and/or configuration interaction.

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