JOURNAL ARTICLE

Absolute gas-phase acidities of CH3NH2, C2H5NH2, (CH3)2 NH, and (CH3)3N

G. I. MackayR. HemsworthDiethard K. Böhme

Year: 1976 Journal:   Canadian Journal of Chemistry Vol: 54 (10)Pages: 1624-1642   Publisher: NRC Research Press

Abstract

The flowing afterglow technique has been employed in measurements of the rate and equilibrium constants at 296 ± 2 K for reactions of the type[Formula: see text]and[Formula: see text]where R 1 and R 2 may be H, CH 3 , or C 2 H 5 . The equilibrium constant measurements provided absolute values for the intrinsic (gas-phase) acidities of the Brønsted acids CH 3 NH 2 , C 2 H 5 NH 2 , (CH 3 ) 2 NH, and (CH 3 ) 3 N, the heats of formation of their conjugate bases, and the electron affinities of the corresponding radicals R 1 R 2 N. Proton removal energies, ΔG 0 298 /(kcal mol −1 ), were determined to be 395.7 ± 0.7 for [Formula: see text] 391.7 ± 0.7 for [Formula: see text] 389.2 ± 0.6 for [Formula: see text] and > 396 for [Formula: see text] Heats of formation, ΔH 0 f.,298 , were determined to be 30.5 ± 1.5 for CH 3 NH − , 21.2 ± 1.5 for C 2 H 5 NH − , and 24.7 ± 1.4 for (CH 3 ) 2 N − . Electron affinities (in kcal mol −1 ) were determined to be 13.1 ± 3.5 for CH 3 NH, 17 ± 4 for C 2 H 5 NH, and 14.3 ± 3.4 for (CH 3 ) 2 N. These results quantify earlier conclusions regarding the intrinsic effects of substituents on the gas-phase acidity of amines and provide an experimental assessment of recent molecular orbital calculations of proton removal energies for alkylamines.

Keywords:
Chemistry Gas phase Standard enthalpy of formation Equilibrium constant Reaction rate constant Proton Analytical Chemistry (journal) Physical chemistry Kinetics Physics Organic chemistry

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Citation History

Topics

Atmospheric Ozone and Climate
Physical Sciences →  Earth and Planetary Sciences →  Atmospheric Science
Atmospheric chemistry and aerosols
Physical Sciences →  Earth and Planetary Sciences →  Atmospheric Science
Advanced Chemical Physics Studies
Physical Sciences →  Physics and Astronomy →  Atomic and Molecular Physics, and Optics

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