Δ(ΔS ‡) and Δ(ΔS) for the Competing Bond Cleavage Reactions in (CH 3CN)(ROH)H + [R = CH 3, C 2H 5, C 3H 7, (CH 3) 2CH]

• Published in: Journal of the American Society for Mass Spectrometry 2005-12, Vol.16 (12), p.2039-2044
• Main Authors: Grabowy, Julie A.D., Mayer, Paul M.
• Format: Article
• Language: English
• Subjects: Acetonitriles - analysis; Acetonitriles - chemistry; Alcohols - analysis; Alcohols - chemistry; Binding Sites; Chemistry; Computer Simulation; Entropy; Exact sciences and technology; Mass spectrometry; Models, Chemical; Organic chemistry; Protons; Reactivity and mechanisms
• ISSN: 1044-0305; 1879-1123
• DOI: 10.1016/j.jasms.2005.08.010

Microcanonical variational transition-state theory was used to determine the entropies of activation for hydrogen-bond cleavage reactions leading to CH 3CN + ROH 2 + in a series of acetonitrile-alcohol proton-bound pairs (CH 3CN)(ROH)H + (where R = CH 3, CH 3CH 2, CH 3CH 2CH 2, and (CH 3) 2CH). In each case, the dissociation potential surface was modelled at the MP2/6-31 + G(d) level of theory. The dissociating configurations having the minimum sums-of-states were identified in each case and the resulting entropies of activation were calculated. Combined with previous work on the competing reaction leading to CH 3CNH + + ROH, the results permitted the determination of the Δ(ΔS ‡) in each proton-bound pair. For the (CH 3CN)(CH 3OH)H + and (CH 3CN)(CH 3CH 2OH)H + proton-bound pairs, the entropies of activation for the two dissociating channels are essentially the same [i.e., Δ(ΔS ‡) = 0], while Δ(ΔS ‡) for the propanol-containing pairs ranged between 40 and 45 J K −1 mol −1. The latter non-zero values are due to a combination of the location of the dividing surface in each dissociation and the rapidity with the frequencies of the vanishing vibrational modes go to zero as they are converted to product translations and rotations during the dissociation.