Partitioning of the Internal Rotation Barriers in Acetaldehyde: Effect of Fluorine Substitution

Abstract The present work attempts to provide an in‐depth understanding of the internal rotation barrier in acetaldehyde and its fluorine‐substituted analogues by dissecting the energy profile of internal rotation into steric, electrostatic, exchange‐correlation and Pauli repulsion energy terms according to the DFT‐steric‐based energy decomposition analysis. For CH 3 CHO and CF 3 CHO the barrier forming steric, electrostatic and exchange‐correlation effects are found to be largely compensated by the Pauli repulsion term. In CH 2 FCHO and CHF 2 CHO the relative contributions of the various energy components do not follow a monotonous pattern, rather is found to vary throughout the entire energy profile for internal rotation of CH 2 F/CHF 2 group. The relative contributions of the classical and quantum effects to the formation of the internal rotation barriers are highlighted in this context. To this effect, the hybrid density functional B3LYP is employed coupled with the split‐valence, triple‐ζ 6–311++g(3df,2p) basis set that incorporates diffuse functions and additional polarization functions (on heavy atoms).