Experimental Validation of the α-Effect in the Gas Phase

The alpha-effect-enhanced nucleophilicity of an anion with a lone pair of electrons adjacent to the attacking atom-has been well documented in solution; however, there is continuing disagreement about whether this effect is a purely solvent-induced phenomenon or an intrinsic property of the alpha-nudeophiles. To resolve these discrepancies, we explore the alpha-effect in the bimolecular nudeophific substitution reaction in the gas phase. Our results show enhanced nucleophilicity for HOO(-) relative to normal alkoxides in three separate reaction series (methyl fluoride, anisole, and 4-fluoroanisole), validating an intrinsic origin of the alpha-effect. Caution must be employed when making comparisons of the alpha-effect between the condensed and gas phases due to significant shifts in anion basicity between these media. Variations in electron affinities and homolytic bond strengths between the normal and alpha-anions indicate that HOO- has distinctive thermodiemical properties.