The Standard Enthalpy of Formation of the 1-Adamantyl Cation in the Gas Phase. An Experimental and ab Initio Re-assessment

Abstract

The standard molar enthalpy of formation of gaseous 1-adamantyl chloride (1Cl,g) was determined experimentally by means of thermochemical techniques. Ab initio quantum-chemical calculations at the G2-(MP2) level were performed on adamantyl cation (1 + ) and on 1Cl. Combination of these data with other experimental and computational results for adamantane (1H), isobutane (2H), tert-butyl cation (2 + ), and tertbutyl chloride (2Cl) provided purely experimental and purely computational, independent values for the standard enthalpy and Gibbs energy changes for reactions 1 and 2: where X ) Cl. This information was used to determine a value of 162.0 ( 2.0 kcal mol -1 for the standard molar enthalpy of formation of gaseous 1 + , ∆ f H°m(1 + ,g).Holmes and co-workers 1 have recently used appearance energies to determine the standard enthalpy of formation of 1-adamantyl cation (1 + ) in the gas phase, ∆ f H°m(1 + ,g). The value they reported, 152 ( 3 kcal mol -1 , significantly differs from the values obtained by other methods (in the range 158-164 kcal mol -1 ). 1 Inasmuch as carbocations are important chemical species, 2,3 this discrepancy has prompted us to reexamine the problem by means of experimental and computational techniques.Equilibrium techniques, notably ICR (ion cyclotron resonance spectroscopy 4 ), FT ICR (Fourier transform ion cyclotron

Redesigning the rotating-bomb combustion calorimeter

“…Throughout the years, rotating-bomb combustion calorimeters have been used in the study of the thermochemistry of compounds containing sulfur [2,3] and more recently compounds that contain both sulfur and nitrogen [4,5]. Rotating-bomb is also the only way to guarantee adequate reduction of chlorine or bromine in the combustion of halogenated substances [6][7][8] and, even by achieving adequate dissolution of refractory oxides produced after combustion, this device is a reliable instrument in the study of some organometallic compounds [9,10].…”

12 Organic gas-phase ion chemistry

“…30 kJ mol Ϫ1 higher than the BDE in isobutane, 144 and is higher than theoretical predictions. 145 The difference is attributed to error in the adiabatic ionization energy of the adamantyl radical. By using calorimetry and FT-ICR, Abboud et al 146 investigated the thermodynamic stability of 2-adamantyl cation.…”

Determination of the energies of combustion and enthalpies of formation of nitrobenzenesulfonamides by rotating-bomb combustion calorimetry

“…For several years, the main task of our research group has been the determination of the enthalpies of formation of different compounds using combustion calorimetry techniques. We then try to relate the experimental values to the respective molecular structures [4][5][6].…”