Effect of electron-donating and electron-withdrawing atoms on the C–H…Y hydrogen bond in model X₃CH…YZ (X = B, F; YZ = BF, CO, N₂) complexes

ABSTRACT

A computational study of model complexes X₃CH…YZ (X = B, F; YZ = BF, CO, N₂) was undertaken to assess the effect of electron-donating and electron-withdrawing X atoms on the properties of the C–H…Y hydrogen bond. Sequential substitution of the B atoms in B₃CH by F atoms to produce F₃CH allowed for the elucidation of interesting trends in the corresponding hydrogen-bonded complexes. The dipole moments and the dipole moment derivative with respect to C–H bond displacement for the proton donors and the chemical hardness of the Y atom of the proton acceptor YZ were found to be useful parameters for understanding these trends. It was found that a positive dipole derivative favours red-shifted hydrogen bonds, whereas a negative dipole derivative favours blue-shifted hydrogen bonds. However, decreasing hardness of Y (which correlates with increasing intermolecular attraction) modifies the interaction such that either greater C–H bond extensions/red shifts or smaller C–H bond compressions/blue shifts are obtained.

KEYWORDS:

• Hydrogen bond
• blue shift
• dipole moment derivative
• chemical hardness
• haloalkane

Disclosure statement

No potential conflict of interest was reported by the authors.