Steric effects on alkyl cation affinities of maingroup-element hydrides

We have carried out an extensive exploration of gas‐phase alkyl cation affinities (ACA) of archetypal anionic and neutral bases across the periodic system using zeroth order regular approximation‐relativistic density functional theory at BP86/QZ4P//BP86/TZ2P. ACA values were computed for the methyl, ethyl, i‐propyl and t‐butyl cations and compared with the corresponding proton affinities (PA). One purpose of this work is to provide an intrinsically consistent set of values of the 298 K ACA of all anionic (XH) and neutral bases (XH_n) constituted by maingroup‐element hydrides of groups 14–17 and the noble gases (group 18) along the periods 1–6. Another purpose is to determine and rationalize the trend in affinity for a cation as the latter varies from proton to t‐butyl cation. This undertaking is supported by quantitative bond energy decomposition analyses. Correlations are established between PA and ACA values. © 2010 Wiley Periodicals, Inc. J Comput Chem, 2011