Probing Proximal Intramolecular Hydrogen Bonding Interactions on a Norbornane Scaffold

Area of Science:

• Computational Chemistry
• Organic Chemistry
• Molecular Interactions

Background:

• Intramolecular hydrogen bonding plays a crucial role in molecular structure and properties.
• The scope of hydrogen bond acceptors in organic scaffolds is an area of ongoing research.

Purpose of the Study:

• To computationally investigate the potential of various functional groups to act as intramolecular hydrogen bond acceptors.
• To assess the strength and characteristics of hydrogen bonds formed between a hydroxyl (OH) donor and different acceptor atoms (F, Cl, Br, O, S, N, P) within a norbornane framework.

Main Methods:

• Systematic computational study using M06-2X and df-MP2 for geometry optimization.
• High-level single-point energy calculations with PNO-LCCSD(T)-F12.
• Analysis of structural, energetic, vibrational (IR spectroscopy), and electronic properties using Quantum Theory of Atoms in Molecules (QTAIM).

Main Results:

• Conformations with intramolecular OH···A hydrogen bonds exhibited lower electronic energies compared to non-bonded conformations.
• Significant red shifts in OH stretching frequencies and deshielding of the hydrogen atom in NMR spectra were observed for bonded conformations.
• QTAIM analysis confirmed the presence of hydrogen bonds, with electron densities typical for such interactions.

Conclusions:

• Sulfur (S) and Phosphorus (P) containing groups can effectively act as hydrogen bond acceptors, in addition to traditional N and O acceptors.
• The rigid norbornane scaffold facilitates the formation of stable intramolecular hydrogen bonds.
• These findings broaden the understanding of hydrogen bonding capabilities in diverse organic molecules.