A STUDY OF HINDERED ROTATION IN SOME PROTONATED BENZYLAMINES

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Abstract
The effect of hindered rotation upon methylene and ammonio proton shifts and coupling constants of eight protonated benzylamines has been determined. It is shown that the necessary and sufficient condition for methylene proton asymmetry in protonated benzylamines is the absence of a plane of symmetry along the C6H5CH2—N bond axis. It is established that the maximum value of the gauche H—C—N—H+ coupling constant is 3.15 c/s and that the minimum value of the trans H—C—N—H+ coupling constant is 9.45 c/s. From the relative values of the rotationally averaged coupling constants, it is established that the steric effect of the substituent decreases in the following order: isopropyl, phenyl > benzyl ≈ ethyl > methyl. It cannot be decided from the available evidence whether the phenyl group or the isopropyl group causes greater steric hindrance.