Structure and IR spectroscopic behaviour of 2,7-dichloro-1,8-bis(dimethylamino)naphthalene and its protonated form

X-ray diffraction and IR spectroscopic studies on the proton sponge 2,7-dic hloro- 1,8-bis(dimethylamino)naphthalene and its adduct with HBr were perfo rmed. It was shown that the presence of the chlorine atoms in positions 2 a nd 7 leads to some change of conformation with respect to the free molecule . The main factor determining the conformation remains the repulsion of the nitrogen lone electron pairs. However, the repulsion between the methyl gr oups and chlorine atoms causes the dimethylamino groups to be slightly less twisted compared with unsubstituted dimethylaminonaphthalene. The protonat ion leads to the formation of a symmetrical cation (symmetry plane passing through the C9-C10 axis) with the N . . . N distance equal to 2.561(3) Angs trom. This corresponds to the situation when the barrier to the proton tran sfer should be very low. As in other short [NHN](+) bridges, one observes t he IR absorption band at about 500 cm(-1), assigned to the transition betwe en the split O+ --> O- vibrational levels. A very high frequency isotopic r atio (nu(H)/nu(D) = 1.8) is observed for this transition. Copyright (C) 199 9 John Wiley & Sons, Ltd.