Experimental Determination of Activation Energies for Gas-Phase Ethyl and n-Propyl Cation Transfer Reactions

Alkyl cation transfer reactions between ethanol and protonated ethanol and ethanol and protonated propionitrile, as well as between n-propanol and protonated n-propanol have been investigated experimentally by low-pressure Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry. The two ethyl cation transfer reactions were found to be the dominant reaction channels with association being only a minor reaction pathway. The n-propyl cation transfer reaction was found to compete with the association pathway resulting in an approximately 50:50 mixture of protonated di-n-propyl ether and the proton-bound dimer of n-propanol, depending on temperature and pressure. The enthalpies of activation were determined to be −16.1 ± 0.8, −17.5 ± 0.8, and −15.7 ± 0.9 kJ mol-1 for the ethanol/protonated ethanol, ethanol/protonated propionitrile, and n-propanol/protonated n-propanol alkyl cation transfer reactions, respectively. The entropies of activation were found to be essentially the same, −121 ± 28 J K-1 m...