GAS-PHASE ACIDITY OF N2O2H2 AND REACTIONS OF N2O2H- WITH ALIPHATIC-ALCOHOLS

We report the atmospheric pressure gas phase ion-molecule chemistry of the N2O2H- (m/z = 61) anion which is formed when certain hydrogen ato m containing molecules are added to an N2O/Ar mixture in an atmospheri c pressure ionization mass spectrometer (Ni-63-APIMS) source at pressu res of similar to 1 atm and temperatures ranging from 373 to 600 K. By using the bracketing method, the gas phase acidity of N2O2H2 is found to be about the same as that of m-nitrotoluene Delta H-acid(g(degrees )) less than or equal to 365 kcal/mol. The rate constant for proton ab straction from nitromethane is comparable to other proton transfer rea ctions, k(t) = (2 +/- 0.4) x 10(-10) cm(3) molecule(-1) s(-1). N2O2H- reacts with aliphatic alcohols to form esters rather than by proton ab straction. The rate constant for esterification is 10-100 times lower than the rate constant for proton abstraction from nitromethane. SCF-M O calculations show that there are at least six local minima in the po tential energy surface involving N2O2-. The structure with two oxygens bound to one nitrogen with a C-2 nu geometry, NNO2, corresponds to th e global minimum. It is the only form with a calculated vertical elect ron affinity which is greater than 3.49 eV and will not undergo photod etachment at that energy as has been observed experimentally. Similar results are obtained for N2O2H-. The calculated heat of formation of t he C-2 nu form of N2O2H- is -37.32 kcal/mol.