Please use this identifier to cite or link to this item: http://hdl.handle.net/10397/21012
Title: Experimental validation of Gaussian-3 lithium cation affinities of amides : implications for the gas-phase lithium cation basicity scale
Authors: Tsang, Y
Siu, FM
Ma, NL
Tsang, CW
Issue Date: 2002
Publisher: John Wiley & Sons
Source: Rapid communications in mass spectrometry, 2002, v. 16, no. 3, p. 229-237 How to cite?
Journal: Rapid communications in mass spectrometry 
Abstract: Using a refined Gaussian-3 (G3) protocol, the highest level of ab initio calculations reported so far, we have established the Li+ cation binding enthalpy (affinity) at 0 K (in kJ mol-1) for formamide (195.7), N-methylformamide (209.2), N,N′-dimethylformamide (220.0), acetamide (211.7), N-methyl-acetamide (222.5), and N,N′-dimethylacetamide (230.1), with an estimated maximum uncertainty of ±8 kJ mol-1. With these six theoretical lithium cation binding affinities as reference values, the absolute Li+ affinities of imidazole and dimethoxyethane were determined by the extended kinetic method, and by adopting the statistical data treatment protocol recently proposed by Armentrout. The Li+ affinities obtained for these two ligands are in good agreement (within 6 kJ mol-1) with recent values determined by the threshold collision-induced dissociation method, and consistent with the Li+ basicity values first reported by Taft and co-workers in 1990. Our study confirms that the previously suggested, and recently implemented, downward revision of Taft's original basicity scale by 10.9 kJ mol-1 is justified for ligands with revised basicities less than 151 kJ mol-1. However, for selected ligands with Li+ basicities greater than 151 kJ mol-1, including some of the six amides studied in this work, the reported discrepancy between theoretical and experimental estimates in the revised Li+ basicity scale of Burk et al. is likely to arise from experimental uncertainties.
URI: http://hdl.handle.net/10397/21012
ISSN: 0951-4198
EISSN: 1097-0231
DOI: 10.1002/rcm.570
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