VAPOR-PRESSURE ISOTOPY AND HYDROGEN-BONDING OF RING-DEUTERATED CYCLOPROPYLAMINES

The vapour pressure ratios of the pairs C3D5NH2-C3H5NH2 and C3D5ND2-C3H5NH2 determined from difference measurements in the range 283-333 K can satisfactorily be described by the equations ln[P(C3D5NH2)/P(C3H5NH2)] = (233.19 +/- 324.054)(K/T)2 + (10.003 +/- 1.056)K/T and ln[P(C3D5ND2)P(C3H5NH2)] = -(6142.40 +/- 340.479)(K/T)2 + (25.522 +/- 1.101)K/T Unlike the values P(CD3ND2)/P(CH3NH2) for methylamine, in the investigated temperature range the ratios P(C3D5ND2)/P(C3H5NH2) are greater than unity. The higher values follow mainly from a distinctly smaller normal effect for amino group deuteration and a greater inverse effect for alkyl group deuteration. Analysis suggests an association of cyclopropylamine which is considerably weaker than for methylamine, and like the association of isopropylamine, slightly less than that of n-propylamine. The same sequence of association strengths is derived from the differences in vaporization enthalpies. These results are in agreement with spectroscopic data and can be explained by steric factors and, possibly, by the influence of the higher acidity of cyclopropylamine. Calculations of the boiling points of the deutcroisomers correspond to the concepts developed for the association from the vapour pressure ratios.