An enthalpic scale of hydrogen-bond basicity, part 1: halogenoalkanes

Hydrogen bond enthalpies DeltaH degrees for the interaction of 4-fluorophen ol with 18 fluoro-, chloro-, bromo-, and iodo-alkanes in CCl4 solution have been determined through the temperature variation of hydrogen-bond equilib rium constants. A statistical analysis of the DeltaH degrees-DeltaS degrees correlation shows that this extrathermodynamic relationship is valid for t he family of halogenoalkanes. The enthalpic data are also used to test the correlation of DeltaH degrees versus Deltav(OH), the IR frequency shifts of the OH band of 4-fluorophenol caused by the hydrogen bonding (the Badger-B auer relationship). This relationship is family dependent, and, for fluoroa lkanes and iodoalkanes, does not pass through the origin. These findings al low a safer use of the Badger-Bauer relationship to predict hydrogen-bond e nthalpies accurately. Copyright (C) 2001 John Wiley & Sons, Ltd.