Chlorodifluoroacetyl Isothiocyanate, ClF2CC(O)NCS: Preparation and Structural and Spectroscopic Studies

LUIS A. RAMOS; SONIA E. ULIC; ROSANA M. ROMANO; YURY V. VISHNEVSKIY; NORBERT W. MITZEL; HELMUT BECKERS; HELGE WILLNER; SCHENGRUI TONG; MAOFA GE; CARLOS O. DELLA VÉDOVA

JOURNAL OF PHYSICAL CHEMISTRY A

AMER CHEMICAL SOC

Lugar: Washington; Año: 2013 vol. A p. 5597 - 5606

1089-5639

Chlorodifluoroacetyl isothiocyanate, ClF2CC(O)NCS, wassynthesized by the reaction of ClF2CC(O)Cl with an excess of AgNCS. Thecolorless product melts at −85 °C, and its vapor pressure follows the equationln p = −4471.1 (1/T) + 11.35 (p [atm], T [K]) in the range −38 to 22 °C.The compound has been characterized by IR (gas phase, Ar matrix, and matrixphotochemistry), by liquid Raman, by 19F and 13C NMR, gas UV−vis, andphotoelectron spectroscopy (PES), by photoionization mass spectrometry(PIMS), and by gas electron diffraction (GED). The conformational propertiesof ClF2CC(O)NCS have been analyzed by joint application of vibrationalspectroscopy, GED and quantum chemical calculations. The existence of twoconformers has been detected in the gas and liquid phases, in which the C−Clbond adopts a gauche orientation with respect to the CO group; the COgroup is in syn- or anti-position with respect to the NC double bond of theNCS group. The computed ΔG° difference between these two gauche−syn and gauche−anti forms is ΔG° = 0.63 kcal mol−1 inthe B3LYP/6-31G(d) approximation. The most significant gas-phase structural parameters for gauche−syn ClF2CC(O)NCS arere(NCS) 1.559(2) Å, re(NCS) 1.213(2) Å, re(NC) 1.399(7) Å, re(CO) 1.199(2) Å, and ∠e(CNC) 134.7(13)°.Photolysis of ClF2CC(O)NCS using an ArF excimer laser (193 nm) mainly yields ClF2CNCS, CO, and ClC(O)CF2NCS. Thevalence electronic properties of the title compound were studied using PES and PIMS. The experimental first vertical ionizationenergy of 10.43 eV corresponds to the ejection primarily of the sulfur lone-pair electrons of the in-plane nonbonding orbital onthe NCS group.