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

The vapour pressure ratios of the pairs C3D5NH2-C3H5NH2 and C3D5ND2-C3 H5NH2 determined from difference measurements in the range 283-333 K c an satisfactorily be described by the equations ln[P(C3D5NH2)/P(C3H5NH 2)] = (233.19 +/- 324.054)(K/T)2 + (10.003 +/- 1.056)K/T and ln[P(C3D5 ND2)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 investi gated temperature range the ratios P(C3D5ND2)/P(C3H5NH2) are greater t han unity. The higher values follow mainly from a distinctly smaller n ormal effect for amino group deuteration and a greater inverse effect for alkyl group deuteration. Analysis suggests an association of cyclo propylamine which is considerably weaker than for methylamine, and lik e the association of isopropylamine, slightly less than that of n-prop ylamine. The same sequence of association strengths is derived from th e differences in vaporization enthalpies. These results are in agreeme nt 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 t o the concepts developed for the association from the vapour pressure ratios.