Premium
Theoretical study of substituent effects on the acidity of the methyl group: Structure of anions CH 2 X −
Author(s) -
Hopkinson A. C.,
Lien M. H.
Publication year - 1980
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.560180604
Subject(s) - chemistry , carbanion , substituent , electronegativity , proton affinity , deprotonation , affinities , basis set , proton , methyl group , molecule , protonation , computational chemistry , crystallography , stereochemistry , medicinal chemistry , ion , group (periodic table) , density functional theory , organic chemistry , physics , quantum mechanics
Geometries have been optimized using molecular‐orbital calculations (a) with a 4‐31G Gaussian basis set for carbanions CH 2 X − where X = H, CH 3 , NH 2 , OH, F, CCH, CHCH 2 , CHO, COCH 3 , CN, and NO 2 ; and (b) with an STO ‐3G basis set for methyl acetate and acetyl deprotonated methyl acetate. All the carbanions containing unsaturated substituents are planar, with a considerable shortening of the CX bond. Carbanions containing saturated substituents are pyramidal with the out‐of‐plane angle α increasing with the electronegativity of the substituent. Double‐zeta basis set calculations give proton affinities over the range 449 (for CH 3 CH 2 − ) to 355 kcal/mol (for CH 2 NO 2 − ), with all unsaturated anions having smaller affinities than saturated anions. The correlation of proton affinities with 1 s binding energies, and with charges on both the carbon of the anion and on the acidic proton of the neutral molecule are examined.