Proton affinity of peroxyacetyl nitrate. A computational study of topical proton affinities

Abstract

The structure and energetics of the peroxyacetyl nitrate conformers syn- and anti-PAN and several cations formed by PAN protonation were investigated by a combination of density functional theory and ab initio calculations. syn-PAN is the more stable conformer that is predicted to predominate in gas-phase equilibria. The acetyl carbonyl oxygen was found to be the most basic site in PAN, the oxygen atoms of the peroxide and NO(2) groups being less basic. The 298 K proton affinity of syn-PAN was calculated as 759-763 kJ mol(-1) by effective QCISD(T)/6-311 + G(3df,2p) and 771-773 kJ mol(-1) by B3-MP2/6-311 + G(3df,2p). The calculated values are 25-39 kJ mol(-1) lower than the previous estimate by Srinivasan et al. (Rapid Commun. Mass Spectrom. 1998; 12: 328) that was based on competitive dissociations of proton-bound dimers (the kinetic method). The calculated threshold dissociation energies predicted the formation of CH(3)CO(+) + syn - HOONO(2) and CH(3)COOOH + NO(2)(+) to be the most favorable fragmentations of protonated PAN that required 83 and 89 kJ mol(-1) at the respective thermochemical thresholds at 298 K. The previously observed dissociation to CH(3)COOH + NO(3)(+) was calculated by effective QCISD(T)/6-311 + G(3df,2p) to require 320 kJ mol(-1). The disagreement between the experimental data and calculated energetics is discussed.

Identification of Organic Nitrates in the NO3Radical Initiated Oxidation of α-Pinene by Atmospheric Pressure Chemical Ionization Mass Spectrometry

“…The most intense fragment in the MS/MS scan (Figure a) corresponds to loss of NO 2 ( m / z 200), with a weaker peak corresponding to loss of HOONO 2 ( m / z 167). Loss of HOONO 2 from protonated peroxyacetyl nitrate (CH 3 C(O)OONO 2 , PAN) has been predicted theoretically and also suggested by chemical ionization MS where a CH 3 CO + fragment at m / z 43 indicates elimination of HOONO 2 or (O 2 + HNO 2 ) from PAN . The m / z 200 peak observed in the Q1 scans (Figure ) is exclusively due to fragmentation of the m / z 246 parent peak.…”

Measurement of alkyl and multifunctional organic nitrates by proton-transfer-reaction mass spectrometry

“…Only few available data can be found concerning the PA of organic nitrates, which were calculated using ab initio quantum mechanical methods exclusively. The PA of organic nitrates has been estimated to be 740 kJ mol −1 for methyl nitrate (Lee and Rice, 1992), 753 kJ mol −1 for ethyl nitrate (Kriemler and Buttrill, 1970), 748 kJ mol −1 for methyl peroxynitrate (Ravelo and Francisco, 2007) and 759-773 kJ mol −1 for peroxyacetyl nitrate (Tureček, 2000). These studies show that the PA of organic nitrates is higher than that of water, so that proton transfer reaction may occur.…”

Elucidating the mass spectrum of the retronecine alkaloid using DFT calculations

“…In this case, the basis set was increased to 6‐311+G(d) to improve the accuracy of the barrier height values. This approach has been used successfully to describe the derivatives of peroxyacetyl nitrate and naphthoquinone thereby leading to an improved agreement with experiment . The effect of basis sets larger than 6‐311+G(d) was tested, but we did not find any significant differences in the values of the barriers heights, as can be seen in Table S1.…”