Hydrogen fluoride bond enthalpy

The only measured enthalpy of vaporization is for n-butyl lithium, 107.1 2.9 kJmoU, from which the constant b(Li) in equation 4 is derived as 85 kJmoU. This is a hefty value compared to fc(OH) = 29, b(—S(0)2—) = 53 and b(CY) = 11 kJmoU. However, the oligomeric states of the organolithium liquid and gas phases are not known with certainty. This is reminiscent of problems for hydrogen-bonded species such as carboxylic acids and hydrogen fluoride. 

In a recent thermodynamic and spectroscopic study Redington66 -68) evaluated AH and AS for the formation of cyclic and open-chain oligomers of hydrogen fluoride. His best fit to vapor density, heat capacity, excess entropy, excess enthalpy, and infra red absorption data shows a monotonous increase in AH per hydrogen bond with increasing number of HF molecules both for open-chain and cyclic clusters, using the relation... 

A topic related to that of the gas-phase acidities of phenols is the quest for quantitative data on the thermodynamic stability of hydrogen-bonded complexes, or clusters , [ArO-H X ] and [ArO H-X] between phenols and various anions derived from other Brpnsted acids. The thermodynamics of cluster formation of the phenolate ion [1 — H] with water, ethanol and acetic acid have been determined by using a pulsed electron-beam mass spectrometer and their stability was found to increase with the gas-phase acidity of the Br0nsted acid. For example, association of [1 — H] with H2O is much weaker. A// = —15.4 kcalmor , than that of [1 — H] with CH3COOH, AHq = —27.4 kcalmor The association enthalpy of the complex of phenol and fluoride ion, [1 F ], has been measured to be A//° = —41.3 kcalmor , much stronger than... 

Libii S, Jasim NA, Perutz RN et al (2008) Metal fluorides form strong hydrogen bonds and halogcm bonds measuring interaction enthalpies and entropies in solution. J Am Chem Soc 130 7842-7844... 

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