ASSOCIATION OF THE AMMONIUM ION WITH ALPHA,OMEGA-ALKANEDIOLS

The association of the ammonium ion with several alpha,omega-alkanedio ls has been studied by high pressure mass spectrometry. Standard entha lpy (kJ mol(-1)) and entropy (J K-1 mol(-1), in parentheses) values de termined for the reaction diol + NH4+ reversible arrow diol . NH4+ are 1,2-ethanediol, 121 +/- 4(125 +/- 2); 1,3-propanediol, 139 +/- 5 (151 +/- 3); 1,4-butanediol, 138 +/- 4 (142 +/- 2); 2,3-butanediol, 146 +/ - 6 (161 +/- 3), and 2-butene-1,4-diol, 135 +/- 6 (148 +/- 4). Compari son with the thermodynamic values for the association of NH4+ with mon ohydric alcohols shows that the association of NH4+ with diols leads t o the formation of cyclic structures with two intermolecular hydrogen bonds and that, unlike protonation. there is little effect of carbon n umber on the values of Delta H degrees and Delta S degrees for the ass ociation. (C) 1998 Elsevier Science B.V.