INTERCONVERSION OF ROC- GAS-PHASE CATALYSIS BY ARGON AND DINITROGEN( AND RCO+ (R = H AND CH3) )

Molecular orbital calculations using density functional theory at the B3LYP/6-311+++G(d,p) level have been used to optimize structures for i ons COR+... M and M .. RCO+ and also for the transition structures COR +... M(ts) for their interconversion (R = H-2 CH3 and M = Ar and N-2). For the unsolvated ions and for ions COH+... M, M ... HCO+, and COH+. .. M(ts) the optimized structures were used for single-point calculati ons at QCISD(T)(full)/6-311++G(2df,p). Critical points on the COH+ and ArCOH+ potential energy surfaces were also optimized at MP2(full)/6-3 11++G(3df,3pd). For the uncomplexed ions COR+, the barriers to 1,2-mig ration of R+ at B3LYP/6-311++G(d,p) are 35.4 kcal mol(-1) for R = H an d 14.2 kcal mol(-1) for R = CH3. Inclusion of a dinitrogen molecule re moves this barrier by permitting COR+ to deposit R+ on N-2 followed by CO retrieving the R+ to produce the lower energy isomer, RCO+. Argon has a lower R+ affinity than the oxygen atom of CO and does not remove R+ from COR+. Preferential stabilization by argon of the transition s tructure for the 1,2-migration of R+ over stabilization of COR+ at the minimum results in a reduction in the barrier to rearrangement. The g as-phase rearrangements of ions COR+ via ''solvated'' transition struc tures COR+... Ar(ts) are calculated to have barriers of 8.3 kcal mol(- 1) for R = H and 5.7 kcal mol(-1) for R = CH3, while for COH+... Ar at MP2(full)/6-311++G(3df,3pd) the barrier is only 2.0 kcal mol(-1). The se findings indicate noble gas atoms may catalyze the rearrangement of cations rather than simply cool them by collisions.