On The Steric Hindrance of Bulky Substituents - Determination of Their Cone Angles

A series of simple halogen compounds was studied with respect to steric hindrance by means of quantum mechanical methods utilizing the M062X/aug-cc-pvdz level of theory. The maximal cone angles of the halogen compounds R-E were computed for a series of different substituents (R carbon or silyl based substituents, E = halogen). Depending on the substitution pattern and the bulkiness of the substituent R a correlation between the cone angle and structural parameters is discussed. Estimates for the cone angles of any element attached to R are provided, that allows comparison of cone angles of different substituents at different distances, which can facilitate synthesis. Additionally, the bonding situation was assessed by natural bond orbital (NBO) analysis indicating that significant electronic effects should be considered when changing from silyl to carbon based substituents. Silyl based substituents display a considerably larger charge transfer to E compared to carbon based once.