Gas-Phase Structures of Acetyl Peroxynitrate and Trifluoroacetyl Peroxynitrate

Abstract

The molecular structures and conformational properties of acetyl peroxynitrate (PAN, CH3C(O)OONO2) and trifluoroacetyl peroxynitrate (FPAN, CF3C(O)OONO2) were investigated in the gas phase by electron diffraction (GED), microwave spectroscopy (MW), and quantum chemical methods (HF/3-21G, HF/6-31G*, MP2/6-31G*, B3PW91/6-31G*, and B3PW91/6-311+G*). All experimental and theoretical methods show the syn conformer (C=O bond of acetyl group syn to O-O bond) to be strongly predominant relative to the anti conformer. The O-NO2 bonds are extremely long, 1.492(7) A in PAN and 1.526(10) A in FPAN, which correlates with their low bond energy and the easy formation of CX3C(O)OO* and *NO2 radicals in the atmosphere. The O-O bonds (1.418(12) A in PAN and 1.408(8) A in FPAN) are shorter than that in hydrogen peroxide (1.464 A). In both compounds the C-O-O-N dihedral angle is close to 85 degrees.

Ab initio and DFT Study of the Structural Properties and Thermochemistry of CH3S(O)2OONO2 Atmospheric Molecule and CH3S(O)2OO· Radical

“…The calculated O-N bond length (1.547 Å) is slightly longer than those found in other peroxy nitrates that vary between 1.49 and 1.53 Å. 22,42 The geometries of CH 3 S(O) 2 OO• and CH 3 S(O) 2 O• radicals ( Figure 3) were optimized at different levels and their structural parameters are provided in Table 4. In CH 3 S(O) 2 OO•, the S-O single bond is prolonged to be 1.762 Å (UB3LYP/6-311＋＋G(3df,3pd)).…”

“…The -OONO 2 group in peroxy nitrates provides a 22 and CH 2 ＝ CHC(O)OONO 2 (86.4°). 41 The obtained O-O bond length of 1.402 Å is quite close to that of CH 2 ＝CHC-(O)OONO 2 (1.395 Å), 41 which was also calculated at the B3LYP/6-311＋＋G(3df,3pd) level.…”

Fluorocarbon oxy and peroxy radicals

“…After trap-to-trap condensation of the crude product in vacuo and by treatment with NaHCO 3 it was possible to measure the missing physical and spectroscopic properties of pure CF 3 C(O)OONO 2 and to determine its gas phase structure [126,127].…”

Gas Phase Structures of Peroxides: Experiments and Computational Problems

“…[72,74,75] The most remarkable structural feature of these peroxides is the extremely long NÀO bond. Gas-phase structures of covalent nitrates XONO 2 demonstrate that the NÀO single bond length depends strongly on the electronegativity of the substituent X.…”