Double proton transfer in crystals of 1,3,4,6,7,8-hexahydro-2H-pyrimido[1, 2-a] pyrimidine (hppH):13C and15N CPMAS NMR study of (hppH)2

Abstract

Abstract In this paper, we report an example of intermolecular solid-state proton transfer in the bicyclic guanidine, hppH. A combination of X-ray crystallography, CPMAS NMR (13C and 15N) and theoretical calculations allows us to determine that a double proton transfer takes place in the (hppH)2 dimer with an activation energy of about 50kJmol -1. According to the B3LYP/6-311 ++G(d,p) calculations, the double proton transfer occurs non-symmetrically through azwitterion. Copyright © 2009 John Wiley & Sons, Ltd.