Effect of the Substituents on the Nature and Strength of Lone-Pair–Carbonyl Interactions in Acyl Halides

Abstract

We have performed a combined structural and theoretical analysis of lone paircarbonyl interactions in several families of acyl halides (R-CO-X). CSD searches have allowed us to establish the geometrical preferences for such short contacts.The study of the molecular electrostatic potential (MEP) of several molecules along with energy decomposition analyses (EDA) disclosed the nature of the interaction and the factors that affect its strength. To further understand lone pair-carbonyl contacts we have systematically analysed, by means of DFT calculations, the effect of the lone pair as well as of the halogen atom (X) and the substituent attached to the carbonyl group (R). Interaction energies up to 8 kcal/mol suggest that these interactions can be exploited in crystal design and supramolecular chemistry.

Methyl Groups as Hydrogen Bond Acceptors via Their sp3Carbon Atoms

“…Remarkably, both the E–C···H (Figure A) and C···H–Y (Figure B) angles tend to 180° as the C···H distance shortens, which is consistent with the existence of a hydrogen bond-like interaction. Such behavior has been previously observed in similar interactions, and it is characteristic of significantly directional interactions. − …”

Understanding the Interplay of Dispersion, Charge Transfer, and Electrostatics in Noncovalent Interactions: The Case of Bromine–Carbonyl Short Contacts

“…Nevertheless, a deep knowledge of the origin of a given interaction is crucial to control and eventually exploit it at the nanoscale, in crystal engineering or materials design. Especially difficult is to distinguish between the contribution of orbital mixing and electrostatic attraction in σ- and π-hole interactions because the empty orbital and the electron density hole, responsible for the latter and the former, respectively, are located at the same region of the molecule. − This fact has lead, for instance, to a longlasting debate about the dipolar or orbital nature of carbonyl–carbonyl interactions in proteins and organic molecules. , Moreover, recent reports have also pointed out the possibility of having attractive interactions between atoms that are electrostatically equivalent, for which the prediction of an attraction based on the molecular electrostatic potentials is no longer useful. ,,− …”

Cooperative Effects between Hydrogen Bonds and C═O···S Interactions in the Crystal Structures of Sulfoxides

“…Noncovalent interactions, in their numerous different versions, have attracted increasing interest in recent years due to their central role in many chemical and biological processes. , Much effort has been focused, both experimentally and computationally, on the study of their physical origin and the factors that can affect their strength . It appears now clear that many noncovalent interactions, from triel − to halogen bonding, are the interplay of electrostatics and orbital interactions combined with ubiquitous dispersion forces. , …”

“…3 It appears now clear that many noncovalent interactions, from triel 4−7 to halogen bonding, 8 are the interplay of electrostatics and orbital interactions combined with ubiquitous dispersion forces. 9,10 It has also been seen that some chemical groups can act as both nucleophiles and electrophiles when involved in noncovalent interactions. For instance, carbonyl compounds act as electron density donors and acceptors via the oxygen and carbon atoms, respectively, in carbonyl−carbonyl interactions.…”