Acidity of Substituted Benzenes − An Ab Initio Study of the Influence of Methoxy, Trifluoromethyl and Trifluoromethoxy Groups by a Novel Trichotomy Formula

Abstract

Keywords: Acidity / Aromaticity / Electrostatic field effect / Substituent effectsThe acidities of mono-and polysubstituted benzenes incorporating one, two, or three OCH 3 , OCF 3 , or CF 3 groups were investigated by use of reliable ab initio theoretical models. The calculated deprotonation energies are in very good agreement with available experimental data, although these are unfortunately sparse. A recently developed novel trichotomy formula proved useful for interpretation of predicted variation in acidity in the monosubstituted compounds. In particular, the long-range final state effect in OCF 3 and CF 3 derivatives is confirmed. It is reflected in the stabilization of the lone-pair electrons formed upon deprotonation at the meta and para positions. The theoretically established long-

α-Fluorinated Ethers, Thioethers, and Amines: Anomerically Biased Species

“…The ortho -(trifluoromethoxy)benzenide ion ( 74 ) has been evaluated at the MP2(fc)/6-311+G**//HF/6-31+G* level of theory. Most conformers were found to populate a flat valley that extends from the syn -periplanar to the perpendicular arrangement, and only thereafter the free energy rises slowly to attain a 1.7 kcal/mol maximum at the anti -periplanar state. ,

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“…Its charge-attenuating effect is long-ranging, leveling off only moderately when the substituent is shifted from the ortho through the meta to the para position of the carbanion (Table ). When two or three trifluoromethoxy groups are present in the same molecule, their individual contributions to the overall acidity are essentially additive (Table ) 7 MP-2 ab Initio Proton Affinities of Trifluoromethoxy-Substituted Benzenides Relative to the Phenyl Anion a OCH 3 + 0.5 −1.4 −9.2 −20.2 −20.1 OCF 3 −9.5 −10.9 −16.8 −35.7 −46.0 CF 3 −10.1 −10.7 −13.7 −27.6 −38.5 a Δ H Prot 400.0; all numbers in kcal/mol …”

“…Most conformers were found to populate a flat valley that extends from the synperiplanar to the perpendicular arrangement, and only thereafter the free energy rises slowly to attain a 1.7 kcal/mol maximum at the anti-periplanar state. 130,133 A landmark article published in 1990 probed theoretically the free energy and geometry of fluoromethylamine (75) as a function of the C-F/N-lone pair dihedral angle. 134 The anti-periplanar (180°) conformer which had the longest C-F (1.410 Å) and the shortest C-N bond proved to be electronically stabilized by as much as 7.5 kcal/mol.…”

Gas‐phase acidity ofpara‐substituted benzoic acids—a triadic analysis of substituent effects

“…This computational procedure yields acidities which compare reasonably well with experiment and much more demanding G2 method. [27][28][29][30][31] We have shown that a very useful tool for interpretation of acidities is provided by the triadic formula: 26,32,33 PAðA…”

Relay Propagation of Crowding: The Trifluoromethyl Group as Both an Emitter and Transmitter of Steric Pressure

“…[1,2] At the same time, it is a relatively bulky substituent. [3] Early attempts to metalate (trifluoromethyl)benzene with butyllithium in refluxing diethyl ether proved regiochemically unclean, affording, after trapping with dry ice, a 100:40:1 mixture of 2-, 3-and 4-(trifluoromethyl)benzoic acid in moderate yield (33-48 %).…”