Neighborhood matters: Steric effects on methyl internal rotation and chlorine nuclear quadrupole coupling in 2-fluoro-4-chlorotoluene

The rotational spectrum of 2-fluoro-4-chlorotoluene was studied in the frequency range 4 to 24 GHz by Fourier transform microwave spectroscopy. Fine torsional splittings into doublets were found for all transitions due methyl internal rotation hindered with a barrier about 230 cm−1. In combination quadrupole coupling hyperfine on same order magnitude originating from chlorine nucleus, rich spectral features observed. Rotational and constants 35Cl 37Cl isotopologues natural abundance precisely determined. Results experiment supported quantum chemical calculations at several levels theory Bailey's semi-experimental method constants. χcc tensor element compared those other halogen-substituted toluene derivatives.