A high pressure mass spectrometric study of proton transfer between tri-, tetra-, penta-, and hexamethylbenzene

1986 ◽  
Vol 64 (10) ◽  
pp. 2021-2030 ◽  
Author(s):  
John Alfred Stone ◽  
Xiaoping Li ◽  
Patricia Anne Turner
Keyword(s):  
High Pressure ◽  
Proton Transfer ◽  
Rotational Symmetry ◽  
Mass Spectrometric Study ◽  
Molecular Ions ◽  
Transfer Reactions ◽  
Proton Affinities ◽  
Potential Energy Profile ◽  
Proton Transfer Reactions ◽  
Increasing Temperature

The proton affinities (PA) of some methylaromatic compounds and the rates of proton transfer reactions have been measured using high pressure mass spectrometry. The equilibria studied were of the form [Formula: see text]. Van't Hoff plots yielded the following PA values (kcal mol−1) relative to PA(ethylacetate) = 200.7 as standard: mesitylene 201.0, 1,2,3,5-tetramethylbenzene 203.2, pentamethylbenzene 204.4, hexamethylbenzene 206.6. ΔS0 values for the proton transfer equilibria are not fully determined by changes in rotational symmetry numbers and it is suggested that vibrational and torsional changes must be considered. Proton transfer is slow in both the forward (exothermic) and reverse (endothermic) directions and, in addition, for all except the most endothermic reaction studied (1,2,3,5-tetramethylbenzene + protonated hexamethylbenzene) the rate constants for proton transfer increase with decreasing temperature. Such behaviour can be associated with the potential energy profile along the reaction coordinate for the reaction. A limited number of charge transfer experiments involving molecular ions [Formula: see text] showed that reaction occurs at every collision in the forward (exothermic) direction and the reaction efficiency in the reverse (endothermic) direction is small but increases with increasing temperature.

Rate and equilibrium constant measurements for gas-phase proton-transfer reactions involving H2O, H2S, HCN, and H2CO

1978 ◽  
Vol 56 (2) ◽  
pp. 193-204 ◽  
Author(s):  
Kenichiro Tanaka ◽  
Gervase I. Mackay ◽  
Diethard K. Bohme
Keyword(s):  
Proton Transfer ◽  
Equilibrium Constant ◽  
High Efficiency ◽  
Equilibrium Constants ◽  
Transfer Reactions ◽  
Proton Affinities ◽  
Flowing Afterglow ◽  
Type Formula ◽  
Proton Transfer Reactions ◽  
Simple Molecules

The flowing afterglow technique has been employed in the measurement of rate and equilibrium constants at 296 ± 2 K for unsolvated proton transfer reactions of the type [Formula: see text] and several solvated proton transfer reactions of the type [Formula: see text] where X and Y may be H2O, H2S, HCN, or H2CO. Where possible, direct comparisons are made with similar measurements performed with other techniques. The equilibrium constant measurements provide a measure of the relative proton affinities of H2O, H2S, HCN, and H2CO and absolute values for PA(H2O) = 166.4 ± 2.4 kcal mol−1, PA(H2S) = 170.2 ± 1.8 kcal mol−1, and PA(HCN) = 171.0 ± 1.7 kcal mol−1 when reference is made to PA(H2CO) = 170.9 ± 1.2 kcal mol−1 which can be derived from available thermochemical information. The rate constant measurements reinforce the generalization that unsolvated proton transfer involving simple molecules proceeds with high efficiency and provide information about the influence of solvation on this efficiency.

Flame Ionization of Silicon, Germanium and Tin

1985 ◽  
Vol 38 (3) ◽  
pp. 347 ◽  
Author(s):  
NS Ham ◽  
T McAllister
Keyword(s):  
Mass Spectrometry ◽  
Proton Transfer ◽  
Charge Exchange ◽  
Silicon Germanium ◽  
Diffusion Flames ◽  
Transfer Reactions ◽  
Proton Affinities ◽  
Atomic Ions ◽  
Flame Ionization ◽  
Proton Transfer Reactions

.When compounds of Si , Ge and Sn are added to 2/C6H6 diffusion flames, ions characteristic of the elements are detected in the burnt gases by mass spectrometry. The ions, which are attributed to charge exchange and proton transfer reactions of H3O+, may be divided into three categories, atomic ions, protonated monoxides and protonated oxyacids . Sn gives atomic ions and protonated monoxides, a similar result to Pb , but neither Si nor Ge give atomic ions. This may be a consequence of the lack of Si and Ge atoms in the burnt gases. Ge and Sn give a protonated monoxide, but Si does not. This observation leads to the suggestion that proton affinities of the Group 4a monoxides are in the order CO, SiO < H2O < GeO , SnO , PbO. Protonated silicic and germanic acids are observed in the burnt gases of Si - and Ge -containing flames, but no oxyacids were observed in Sn -or Pb -containing flames. This indicates that the proton affinities of both acids are greater than that of H2O.

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