Collect. Czech. Chem. Commun. 2005, 70, 370-382

Interaction of Polar Groups with a Bulky Hydrocarbon Residue: Polarizability and Steric Effects

Stanislav Böhma and Otto Exnerb,*

a Department of Organic Chemistry, Institute of Chemical Technology, Prague, 166 28 Prague 6, Czech Republic
b Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, 166 10 Prague 6, Czech Republic


Energies of two series of branched hydrocarbon monosubstituted derivatives, 2-substituted 2-methylpropanes and 1-substituted bicyclo[2.2.2]octanes with 19 different substituents were calculated at the B3LYP/6-311+G(d,p) level and compared with the energies of straight-chain 1-substituted butanes. The comparison was carried out in terms of isodesmic homodesmotic reactions, in which the substituent is transferred from one hydrocarbon residue to another. The branched derivatives are mostly stabilized, in the extreme case by as much as 30 kJ mol-1 confirming that the additive rule used for estimating the enthalpies of formation is not valid for branched derivatives. The stabilization energies ∆E for the individual substituents X are not proportional to any known substituent parameters. In the qualitative respect, they are controlled by the first atom of the substituent - similarly as in the straight-chain isomers - but in the case of sterically demanding substituents they are perturbed by a destabilizing steric effect.

Keywords: Substituent effects; Hydrocarbons; Ab initio calculations; DFT; 2-Methylpropanes; Bicyclo[2.2.2]octanes; Butanes.

References: 54 live references.