The tert-butyl ion heat of formation and the isobutene proton affinity

• Published in: Journal of the American Chemical Society Vol. 115; no. 26; pp. 12613 - 12614
• Main Authors: Keister, Jeffrey W, Riley, John S, Baer, Tomas
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 01.12.1993
• Subjects: 400201 - Chemical & Physicochemical Properties; 661300 - Other Aspects of Physical Science- (1992-); AFFINITY; ALKENES; ALKYL RADICALS; BARYONS; BUTENES; BUTYL RADICALS; CHARGED PARTICLES; Chemical thermodynamics; Chemistry; CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; DISSOCIATION; ELEMENTARY PARTICLES; Elements, mineral and organic compounds; ENTHALPY; Exact sciences and technology; FERMIONS; FORMATION HEAT; General and physical chemistry; HADRONS; HALIDES; HALOGEN COMPOUNDS; HYDROCARBONS; INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; IODIDES; IODINE COMPOUNDS; IONIZATION; IONS; NUCLEONS; ORGANIC COMPOUNDS; PHYSICAL PROPERTIES; PROTONS; RADICALS; REACTION HEAT; THERMODYNAMIC PROPERTIES; Isobutene; Proton affinity; Coincidence method; Enthalpy; Carbocation; Experimental study; Thermodynamic properties; Heat of formation; Mass spectrometry; Ethylenic compound
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/ja00079a062

A new value of the tert-butyl ion heat of formation has been measured by dissociative ionization of tert-butyl iodide using the photoelectron photoion coincidence technique. The derived [Delta]H[sub f][degrees][sub 0](t-C[sub 4]H)[sup +] of 734 kJ/mol and [Delta]H[sub f][degrees][sub 298](t-C[sub 4]H[sub 9][sup +]) of 711 kJ/mol is 20 kJ/Mol higher than previous experimental measurements, but agrees within 1 kJ/mol with a recent theoretical ab initio calculation. The derived proton affinity for isobutene is thus 802 kJ/mol at 298 K. With these values established, we predict a tert-butyl radical ionization potential of 6.85 eV, which is close to Houle and Beauchamp's vertical IP from PES (6.92 eV) and Lossing's reported onset of 6.92 eV. However, it is considerably higher than the reported adiabatic IP of 6.7 eV. 24 refs., 1 fig., 1 tab.