Conformational stability, barriers to internal rotation, vibrational assignment andabinitiocalculations of fluoroacetyl chloride

摘要

The far infrared spectrum (375 to 35 cmminus;1) of gaseous fluoroacetyl chloride, CH2FC(O)C1, has been recorded at a resolution of 0.10 cmminus;1. The fundamental asymmetric torsions of the more stabletrans(halogen atoms aretrans) and the high energycisconformations have been observed at 116.18 and 49.42 cmminus;1, respectively, each with several upper state transitions falling to lower frequency. From these spectral data, an asymmetric potential function has been calculated and the potential coefficients are:V1=43plusmn;6,V2=1039plusmn;36,V3=498plusmn;3,V4=149plusmn;21, andV6=minus;10plusmn;7 cmminus;1. Thetranstocisandcistotransbarriers are 1455plusmn;25 cmminus;1(4.16plusmn;0.07 kcal/mol) and 914plusmn;24 cmminus;1(2.61plusmn;0.07 kcal/mol), respectively, with an enthalpy difference of 541plusmn;45 cmminus;1(1.55plusmn;0.13 kcal/mol). From studies of the Raman spectra at variable temperatures, values of 509plusmn;37 cmminus;1(1.46plusmn;0.10 kcal/mol) and 310plusmn;8 cmminus;1(0.89plusmn;0.02 kcal/mol) have been determined for the enthalpy difference for the gas and liquid, respectively. The conformational stability, barriers to internal rotation, and fundamental vibrational frequencies which have been determined experimentally, are compared to those obtained fromabinitioHartreendash;Fock calculations employing both the 3hyphen;21Gast; and 6hyphen;31Gast; basis sets, and to the corresponding quantities obtained for some similar molecules.