This item still needs to be validated !
Title: Protonation of gaseous halogenated phenols and anisoles and its interpretation using DFT-based local reactivity indices
Authors: Tishchenko, Oksana ×
Pham-Tran, NN
Kryachko, ES
Nguyen, Minh Tho #
Issue Date: 2001
Series Title: Journal of Physical Chemistry A vol:105 issue:38 pages:8709-8717
Conference: date:Univ Louvain, Dept Chem, B-3001 Louvain, Belgium; Vietnam Natl Univ, Coll Sci, Fac Chem, Thanh Pho Ho Chi Minh, Vietnam; Bogoliubov Inst Theoret Phys, UA-03143 Kiev, Ukraine
Abstract: The local proton affinities of phenol and its halogenated derivatives, X-C6H4-OH (X = H, F, Cl, Br, and 1) in the C-2 (ortho), C-3 (meta), and C-4 (para) ring carbon positions are determined using DFT and MO methods. Similar to the process in the parent phenol, the C-4-protonation is the most preferable following a X-substitution at either the C2 or C3 position. Except for X = I, in para-X-phenols, a C-2-protonation provides the most stable protonated forms; for para-I-phenol, a C4-protonation remains more favorable. At the modest B3LYP/6-31+G(d,p) + ZPE level, the proton affinities (PA's) are reasonably reproduced with a quasi systematic overestimation of about 10 kJ/moI with respect to available experimental data. The calculated PA's for X-phenols are as follows (values in kJ/mol, 2, 3, and 4 stand for the substitution positions and experimental values are given in parentheses): 2-F, 797 (788); 3-F, 813 (802); 4-17, 787 (776); 2-Cl, 801; 3-Cl, 815; 4-Cl, 789; 2-Br, 806; 3-Br, 818; 4-Br, 792; 2-I, 813; 3-I, 823; and 4-I, 816; with a probable error of 12 kJ/mol. A portion of the potential energy surface describing the excess proton migration over the phenol ring is elaborated. A correlation between the local PA's and the shifts of the nu (OH) and tau (OH) vibrational modes under protonation suggests that a resonance mechanism is likely responsible for the trend of changes in PA. Attempts to rationalize the regioselectivity of protonation are made using local reactivity indices derived from density functional theory, such as the condensed Fukui function (f) and local softness (s). While these indices could predict the preferential protonation site among C(H) atoms at various positions, which are the sites of a similar nature, they are unable to differentiate either a C- or an O-protonation or even the processes at QH) and C(X) atoms. Proton affinities of anisole (C6H5-O-CH3) and fluoroanisole, 845; 2-F, 820 (exptl, 807); 3-F, 835 (826); and 4-F, 809 (796).
ISSN: 1089-5639
Publication status: published
KU Leuven publication type: IT
Appears in Collections:Chemistry - miscellaneous
Quantum Chemistry and Physical Chemistry Section
× corresponding author
# (joint) last author

Files in This Item:

There are no files associated with this item.

Request a copy


All items in Lirias are protected by copyright, with all rights reserved.

© Web of science