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Theoretical study of the proton affinities of 2‐, 3‐, and 4‐monosubstituted pyridines in the gas phase by means of MINDO/3, MNDO, and AM1
Author(s) -
Voets R.,
François J.P.,
Martin J. M. L.,
Mullens J.,
Yperman J.,
Van Poucke L. C.
Publication year - 1989
Publication title -
journal of computational chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.907
H-Index - 188
eISSN - 1096-987X
pISSN - 0192-8651
DOI - 10.1002/jcc.540100403
Subject(s) - mndo , mindo , chemistry , affinities , gas phase , proton affinity , computational chemistry , standard enthalpy of formation , proton , formalism (music) , stereochemistry , molecule , organic chemistry , physics , ion , protonation , quantum mechanics , musical , art , visual arts
Proton affinities (PAs) of 2‐, 3‐, and 4‐monosubstituted pyridines in the gas phase are calculated using the MINDO/3, MNDO, and AM1 methods. The following substituents are considered: F, Cl, CN, CH 3 , CF 3 , CHO, NO 2 , NH 2 , N(CH 3 ) 2 , OCH 3 , and SCH 3 . The results are compared with experimental values. It is found that all MINDO/3 PAs are ca. 6% too high (mean value) compared to the experimental results; on the other hand, the MNDO values are ca. 7% too low (mean value). However, a much better agreement has been observed for the AM1 method where the theoretical values are only ca. 2.4% too low (mean value). Correlations between the calculated proton affinities on one hand and the charges on the acid H atom and Hammett constants on the other hand are studied. Particularly good linear relationships are found for the 4‐monosubstituted compounds within the AM1 formalism.