# Revisiting the Conformational Equilibrium of 1,1,2-Trifluoroethane and 1,1,2,2-Tetrafluoroethane: An NBO Study

## TL;DR

This study explores how fluorine atoms affect the shape and stability of two fluorinated ethane compounds using quantum chemistry and bonding analysis.

## Contribution

The study provides new insights into the conformational preferences of 1,1,2-trifluoroethane and 1,1,2,2-tetrafluoroethane governed by Lewis-type interactions and electron delocalization.

## Key findings

- Lewis-type interactions favor anti-gauche conformers in 1,1,2-trifluoroethane and double anti-gauche in 1,1,2,2-tetrafluoroethane.
- Electron delocalization ensures staggered conformations remain energy minima in both compounds.
- The findings refine understanding of hyperconjugative and electrostatic effects in fluorinated ethanes.

## Abstract

Organofluorine compounds are key to pharmaceutical, agrochemical,
and high-performance material applications, where C–F bond
conformations influence critical properties such as solubility, lipophilicity,
and biological activity. While the conformational behavior of 1,2-difluoroethane
and its characteristic gauche effect is well understood,
the structural preferences of 1,1,2-trifluoroethane and 1,1,2,2-tetrafluoroethane
have remained less explored, particularly in light of hyperconjugation
theory. In this quantum-chemical study, the conformational equilibria
of these two model fluoroalkanes were investigated using density functional
theory and Natural Bond Orbital (NBO) analysis, with complementary
NMR coupling constant calculations. The results reveal that Lewis-type
interactions govern conformational stability, favoring the anti-gauche conformer in 1,1,2-trifluoroethane and the double antigauche conformer in 1,1,2,2-tetrafluoroethane.
Nevertheless, electron delocalization plays an essential role in ensuring
that staggered conformations remain energy minima, as fully localized
electronic structures would yield only a single conformer for each
compound. These findings refine our understanding of hyperconjugative
and electrostatic effects in fluorinated ethanes and provide a more
nuanced framework for predicting conformational preferences in difluoromethyl-containing
systems.