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 (n-1)(-)) 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.
The hetero Diels-Alder reaction of vinyl allenes and aldehydes in the presence of a Lewis acid has been studied both experimentally and theoretically. Differently substituted vinyl allenes and aldehydes were used to obtain information on the structural requirements of the reaction. Theoretical calculations using the density functional theory indicate that the reaction proceeds through a highly asynchronous polar transition state.
We have conducted an extensive computational exploration of how the gas-phase tert-butyl cation affinities (t-BCA) of archetypal anionic and neutral bases across the periodic system are affected by stepwise replacement of all hydrogen atoms at the protophilic center with methyl substituents. This study was conducted using zeroth-order regular approximation relativistic density functional theory (DFT) at the BP86/QZ4P//BP86/TZ2P level. The trends are interpreted in terms of the steric effects of methyl substituents at the protophilic center of the anionic (Me(m)XH(n-1-m)(-)) and neutral bases (Me(m)XH(n-m)). Besides insight, this work also provides an intrinsically consistent set of values of the 298 K tert-butyl cation affinities of all (partially) methyl-substituted or unsubstituted bases constituted by maingroup-element hydrides of groups 14-16 in anionic cases (Me(m)XH(n-1-m)(-)) and groups 15-17 in neutral ones (Me(m)XH(n-m)) along periods 2-6. The effect of long-range dispersion (van der Waals) interactions was estimated through dispersion-corrected density functional theory (DFT-D3) at the BP86-D3/QZ4P//BP86/TZ2P level.
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