Premium
Density functional investigations of carboxyl free radicals: Formyloxyl, acetyloxyl, and benzoyloxyl radicals
Author(s) -
Kieninger Martina,
Ventura Oscar N.,
Suhai Sandor
Publication year - 1998
Publication title -
international journal of quantum chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.484
H-Index - 105
eISSN - 1097-461X
pISSN - 0020-7608
DOI - 10.1002/(sici)1097-461x(1998)70:2<253::aid-qua2>3.0.co;2-t
Subject(s) - chemistry , radical , isomerization , density functional theory , dissociation (chemistry) , ground state , transition state , bond length , computational chemistry , hybrid functional , crystallography , atomic physics , physics , catalysis , crystal structure , biochemistry , organic chemistry
The structure of the lowest electronic states of HCOO · in C 2 v and C s symmetries were optimized employing density functional theory (DFT) methods with extended basis sets including up to f ‐ (on C and O) and d ‐ (on H) polarization functions. Generalized gradient functionals (BLYP) and adiabatically connected functionals (B3LYP and B3PW91) were employed for studying HCOO · , as well as the isomer HOCO · ( trans ), the dissociation limit H · +CO 2 , and the transition state for the decomposition. At the best DFT levels employed, the ground state of HCOO · is 2 A 1 (in C 2 v ) with equal CO bond lengths, while the low‐lying 2 B 2 state is only about 4 kJ/mol above (without inclusion of zero‐point energies). The broken‐symmetry 2 A ′ state (with unequal CO bond lengths, i.e., C s symmetry) is predicted to be about 13 kJ/mol above the 2 A 1 state and to be a transition state for the isomerization HCOO · ( 2 A 1 )→HOCO · ( 2 A ′), with the trans ‐HOCO · isomer about 55 kJ/mol more stable. These facts agree closely with the most recent CASPT2/ANO calculations on this system. Therefore, it is concluded that some DFT models can be used safely for the study of larger radicals of the same type (despite several drawbacks discussed at length in this study). B3PW91, using several basis sets, is subsequently applied to the study of the possible reaction mechanisms of acetyloxyl radical, which exhibits a much more complicated path than formyloxyl, due to the presence of the methyl group. The optimum structures of isomers with coplanar or perpendicular CH and CO bonds were obtained for CH 3 COO · and two saddle points identified on the path of decomposition into CH 3 · and CO 2 . On the other side, saddle points for isomerization into CH 3 OCO · and CH2COOH · were also located, and the decomposition of the former to CH 3 O · +CO investigated. Finally, the structure of the benzoyloxyl radical (C 6 H 5 COO · ) and its possible decomposition products were investigated along the same lines. © 1998 John Wiley & Sons, Inc. Int J Quant Chem 70: 253–267, 1998