Tuning of carbon bonds by substituent effects: an <i>ab initio</i> study

<p>An <i>ab initio</i> study, at the MP2/aug-cc-pVTZ level of theory, is performed to study σ-hole bond in binary XH<sub>3</sub>C···CNY complexes, where X = CN, F, NO<sub>2</sub>, CCH and Y = H, OH, NH<sub>2</sub>, CH<sub>3</sub>, C<sub>2</sub>H<sub>5</sub>, Li. This type of interaction is labelled as ‘carbon bond’, since a covalently bonded carbon atom acts as the Lewis acid in these systems. The geometrical and energetic parameters of the resulting complexes are analysed in details. The interaction energies of these complexes are between −4.97 kJ/mol in (HCC)H<sub>3</sub>C···CNH and −23.07 kJ/mol in (O<sub>2</sub>N)H<sub>3</sub>C···CNLi. It is found that the electrostatic interaction plays a key role in the overall stabilisation of these carbon-bonded complexes. To deepen the understanding of the nature of the carbon-bonding, the molecular electrostatic potential, natural bond orbital, quantum theory of atoms in molecules and non-covalent interaction index analyses are also used. Our results indicate that the carbon bond is favoured over the C-H···C hydrogen bond in the all complexes considered and may suggest the possible important roles of the C···C interactions in the crystal growth and design.</p>