Ion Thermochemistry: Summary of the Panel Discussion
There has been some question regarding the original anchoring of the gas phase acidity scale based on ICR measurements1 in the region of the aliphatic alcohols. The data for methanol from this scale differ by 2.2 kcal/mol from the value from the thermochemical cycle based on bond strength and electron affinity.1,2 Moylan and Brauman have questioned the values for the relative acidities of HF, tBuCH2OH, and PhCH2OH.2 The acidity scale presented in 1979 is based on two assumptions. First, the ion temperature is assumed to be equal to the cell temperature of 320K, so that the slope of a plot of the relative ICR acidities vs. the D-EA absolute values (converted to ΔG°acid as in equation 1) should be unity. Secondly, hydrogen fluoride, with the most accurately known acidity from the D-EA thermochemical cycle, is properly related to the rest of the acidity ladder, so that it may serve as a single point anchor for the whole scale.
KeywordsEffective Temperature Hydrogen Fluoride Panel Discussion Flow Tube Thermochemical Cycle
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