Microwave and far infrared spectra, r structure, barriers to internal rotation, and a b i n i t i o calculations for 2-fluoropropane

Abstract

The microwave spectra of five isotopic species of 2-fluoropropane, (CH3)CH2DCFH, (CH3)2CFD, (CH3)CD3CFH, (CD3)2CFD, and (CH3)213CFH, have been recorded from 12.4 to 39.7 GHz. The b- and c-type R-branch transitions have been observed and assigned for the ground state. Utilizing the rotational constants for these five isotopic species along with those reported earlier for the normal species the following r0 structural parameters have been determined: r(C–C) =1.522±0.007 Å, r(C–F)=1.398±0.013 Å, CCC =113.37±0.79°, and CCF=108.19±0.41°. All of the carbon–hydrogen parameters have also been determined from the rotational constants except for the r(C–Hsec) which was obtained from its frequency in the infrared spectrum. The far infrared spectra of 2-fluoropropane-d0, -d3 and -d7 in the gas phase were recorded with a resolution of 0.10 cm−1. Both torsional fundamentals along with several hot transitions were assigned for the three isotopic species. The barrier to internal rotation of the methyl rotors has been determined with the two-coupled rotor model to be 1149±69 cm−1 (3.29±0.12 kcal/mole). Both potential coupling terms, V33 and V′33, have been determined for the -d0, -d3 and -d7 isotopic species. The complete equilibrium geometry has been determined from ab initio Hartree–Fock gradient calculations employing both the 3-21G and 6-31G* basis sets. These results are compared to the corresponding quantities for some similar molecules.