We. Wentworth et al., GAS-PHASE ACIDITY OF N2O2H2 AND REACTIONS OF N2O2H- WITH ALIPHATIC-ALCOHOLS, Journal of physical chemistry, 98(46), 1994, pp. 11902-11908
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.