Experimentally determined proton affinities of 4- methyl - 3 - penten - 2 -one, 2-propyl ethanoate, and 4-hydroxy -4-methyl-2-pentanone in the gas phase

Abstract

Proton affinities have been determined for 4-methyl-3-penten-2-one. 2-propyl ethanoate. and 4-hydroxy-4-methyl-2- pentanone in the gas phase at 333 K. A quadrupole ion store (QUISTOR) was employed to study mass spectrometrically the equilibrium between a species of known proton affinity and one of the above compounds; equilibrium between protonated species was monitored over an ion storage duration of 100 ms. The values of the proton affinities were found to be 870.5 ± 0.8 kJ m o l l for 4-methyl-3-penten-2-one (mesityl oxide); 842.7 ± 0.6 kJ mol-' for 2-propyl ethanoate: and 831.6 i 0.8 kJ mol-' for 4-hydroxy-4-methyl-2-pentanone (diacetone alcohol).