Methyl groups as widespread Lewis bases in noncovalent interactions

Jorge Echeverría,Oliver Loveday

doi:10.1038/s41467-021-25314-y

Abstract

It is well known that, under certain conditions, C(sp3) atoms behave, via their σ-hole, as Lewis acids in tetrel bonding. Here, we show that methyl groups, when bound to atoms less electronegative than carbon, can counterintuitively participate in noncovalent interactions as electron density donors. Thousands of experimental structures are found in which methyl groups behave as Lewis bases to establish alkaline, alkaline earth, triel, tetrel, pnictogen, chalcogen and halogen bonds. Theoretical calculations confirm the high directionality and significant strength of the interactions that arise from a common pattern based on the electron density holes model. Moreover, despite the absence of lone pairs, methyl groups are able to transfer charge from σ bonding orbitals into empty orbitals of the electrophile to reinforce the attractive interaction.

Highlights

It is well known that, under certain conditions, C(sp3) atoms behave, via their σ-hole, as Lewis acids in tetrel bonding
Noncovalent interactions are the combination of the two effects along with dispersion forces[6,7,8]. It has been accepted in recent years that the name of a noncovalent interaction is given by the nature of the Lewis acids
A question arises: is this behavior reduced to computationally studied hypothetical systems, the methane–water adduct and one particular family of experimental structures? In this work, we show that methyl groups, despite not having an available lone pair, are extensively found behaving as Lewis bases in practically all known major types of noncovalent interactions, including triel, tetrel, pnictogen, chalcogen, and halogen bonding

Summary

Introduction

It is well known that, under certain conditions, C(sp3) atoms behave, via their σ-hole, as Lewis acids in tetrel bonding. Atoms from groups 14, 15, 16, and 17 acting as Lewis acids give rise to tetrel, pnictogen, chalcogen, and halogen bonding, respectively, the physical origin of the attraction is practically the same in all cases: the presence of a region of electron depletion, the σ-hole.

Results

Conclusion