METASTABLE POLYMERS OF THE NITROGEN-OXIDES .1. OPEN-CHAIN NITRIC-OXIDE ANALOGS OF POLYTHIAZYL - A MNDO/AM1 STUDY

The thermodynamics and decomposition kinetics of open chain oligomers of nitric oxide, analogous to the known (SN)x, have been investigated by use of MNDO and AM1. RHF with a limited CI and UHF were used to estimate reaction enthalpies and activation enthalpies. For (NO)n the computed UHF bond lengths, bond orders, and charge alternation were uniform along the chain. The all-trans chains were marginally favored over the cis,trans conformations, unlike the sulfur analogues. The (NO)n oligomers were formed endothermically, in contrast with the (SN)n species, and the charge transfers were less pronounced for (NO)n. Activation barriers for scission of a terminal-NO unit from trans-(NO)n were about 2 or 3 times smaller than those for separation of -SN from cis,trans-(SN)n, but they were still appreciable. Separation of -NONO was less facile. Some AM1 results are also reported with reference to alternative mechanisms for the solid-state polymerization of S2N2. The results suggest that metastable chain polymers of NO analogous to (SN)x may be realizable at elevated temperatures and pressures.