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Density functional theoretical study of p K a of RCOOH (RH, CH 3 , and C 2 H 5 ) using the combination of the extended clusters‐continuum model
Author(s) -
Du Dongmei,
Qin Mei,
Zhou Zhengyu,
Fu Aiping
Publication year - 2011
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/qua.22850
Subject(s) - chemistry , hydrogen bond , carboxylic acid , molecule , hydrogen , density functional theory , cluster (spacecraft) , computational chemistry , coupled cluster , crystallography , organic chemistry , computer science , programming language
The accurate p K a determinations for three carboxylic acids have been investigated using the combination of the extended clusters‐continuum model at B3LYP/6‐31+g(d,p) and B3LYP/6‐311++g(d,p) levels. To take into account of the effect of the water combined with carboxylic acids in different positions, eleven molecular clusters were considered. Among these clusters, the one involving the carboxylic acid wrapped up with water molecules and saturated with hydrogen bonds (four hydrogen bonds around COOH) leads to the best B3LYP p K a results compared to the experimental data. For those clusters saturated with hydrogen bonds, when n = 3 (the number of water molecules), the average absolute errors between the calculated p K a results and experimental data of these three carboxylic acids were 0.19 (0.23) and 0.12 (0.22) p K a at B3LYP/6‐31+g(d,p)//PCM (IEFPCM) and B3LYP/6‐311++g(d,p)//PCM (IEFPCM) levels, respectively; when n = 4, they are 0.53 (1.23) and 1.09 (1.03) p K a , respectively. On the basis of the above results, the molecular cluster saturated with four hydrogen bonds formed by three waters and one carboxylic acid molecule was the chief existence in the carboxylic acid solution. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012