Aliphatic C-H...anion hydrogen bonds: weak contacts or strong interactions?

Area of Science:

• Computational chemistry
• Supramolecular chemistry
• Chemical physics

Background:

• Hydrogen bonds typically involve electronegative atoms like oxygen and nitrogen.
• The hydrogen bond donating ability of C-H bonds is often underestimated.
• Understanding diverse hydrogen bonding interactions is key in molecular recognition.

Purpose of the Study:

• To quantify the hydrogen bond donating strength of aliphatic C-H groups.
• To investigate the influence of substituent effects on C-H hydrogen bond strength.
• To compare the hydrogen bonding capabilities of C-H, O-H, and N-H groups.

Main Methods:

• Utilized ab initio electronic structure calculations.
• Employed the MP2/aug-cc-pVDZ level of theory.
• Calculated hydrogen bond energies for C-H...Cl- interactions.

Main Results:

• Aliphatic C-H groups with electron-withdrawing substituents are moderate-to-strong hydrogen bond donors.
• Calculated interaction energies are comparable to those of O-H and N-H hydrogen bonds.
• Electron-withdrawing substituents significantly enhance the hydrogen bond donating ability of C-H groups.

Conclusions:

• Aliphatic C-H groups can serve as effective hydrogen bond donors in various chemical environments.
• These C-H...anion interactions play a significant role in solution-phase binding.
• The denticity of anion receptors should consider the contribution of C-H hydrogen bonds.