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Geminal Substituent Effects, 15. Enthalpies of Formation of a Series of Fluorinated Hydrocarbons and Strain‐Free Group Increments to Assess Polar and Anomeric Stabilization and Strain
Author(s) -
Schaffer Frank,
Verevkin Sergey P.,
Rieger HansJürgen,
Beckhaus HansDieter,
Rüchardt Christoph
Publication year - 1997
Publication title -
liebigs annalen
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 0947-3440
DOI - 10.1002/jlac.199719970709
Subject(s) - geminal , chemistry , substituent , anomeric effect , anomer , fluorine , stereochemistry , standard enthalpy of formation , crystallography , hydrocarbon , medicinal chemistry , computational chemistry , organic chemistry
Enthalpies of combustion, Δ H c 0 , and enthalpies of vapourization, Δ H vap 0 , for nineteen fluorohydrocarbons containing the groups CF, CF 2 , and CF 3 were measured calorimetrically. From these data, enthalpies of formation, Δ H f (g), were calculated and were partitioned into new strain‐free group increments of the Benson and v. Schleyer type: CH 3 [F] = −42.1; CH 2 [F, C] = −37.1; CH[F, 2 C] = −35.7; C[F, 3 C] = −39.6; CH 2 [2 F] = −61.0; CH[2 F, C] = −71.7; C[2 F, 2 C] = −67.3; CH[3 F] = −110.8; C[3 F, C] = −131.4; C[4 F] = −150.4; F[C] = −195.7 kJ mol −1 . These increments now allow the calculation of the enthalpies of formation of a large family of homologous fluorohydrocarbons. Fluorine substitution, in general, stabilizes saturated hydrocarbon structures. A new concept, which was proposed recently for ethers, acetals, ketals, and orthoesters, for the analysis of the values of the increments for CH 3 , CH 2 , CH, and C groups with their different neighbouring atoms (given in brackets), is successfully applied to fluorohydrocarbons. In this method, the number of pairwise geminal interactions XCY between all attached atoms X and Y is counted. The anomeric stabilization in geminal difluoromethylene groups taken from the FCF interaction is found to be 8 kJ mol −1 smaller than the OCO interaction for acetals and ketals, in agreement with calculations in the literature.