Conformational and Structural Determination of F₂NC(O)F and F₂NC(O)NCO. A Joint Experimental and Theoretical Study

Abstract

The vibrational properties of two difluoroaminocarbonyl species were analyzed by recording the FTIR spectra of the vapor for difluoroaminocarbonyl fluoride, F(2)NC(O)F, and difluoroaminocarbonyl isocyanate, F(2)NC(O)NCO. Moreover, the Raman spectrum of liquid F(2)NC(O)NCO was obtained. Vibrational assignments were made on the basis of a normal coordinate analysis and the evaluation of the band contours appearing in the FTIR spectrum of the vapor. The conformational space of both difluoroaminocarbonyl derivatives were studied by using the B3LYP and MP2 level of theory with extended basis sets [6-311+G(3df) and aug-cc-pVTZ]. Only one conformation belonging to the C(1) symmetry point group is expected for F(2)NC(O)F, whereas the overall evaluation of experimental and theoretical results suggests the existence of a mixture of two conformers for F(2)NC(O)NCO at room temperature. Its relative abundance of the most stable syn form (C=O double bond syn with respect to the N=C=O group) was estimated to be 56(5) %.

Spectroscopic Characterization and Constitutional and Rotational Isomerism of ClC(O)SCN and ClC(O)NCS

“…The intense band observed in the IR spectra at 1819 cm –1 is assigned to the CO stretching mode. Considering that the transition dipole moment of the CO oscillator is almost parallel to the intermediate principal axis of inertia (Figure ), its B-type contour represents a clear experimental evidence for predominance of the syn conformation . Even more, the calculated red-shift (Δν) for the ν­(CO) mode of the anti conformer (36 cm –1 ; B3LYP/6-311+G­(3df)) accounts for the presence of a very weak band at 1780 cm –1 in the gas phase IR spectrum, which is consequently assigned to the ν­(CO) of the anti form.…”

“…Considering that the transition dipole moment of the CO oscillator is almost parallel to the intermediate principal axis of inertia (Figure 5), its B-type contour represents a clear experimental evidence for predominance of the syn conformation. 20 Even more, the calculated red-shift (Δν) for the ν(CO) mode of the anti conformer (36 cm −1 ; B3LYP/6-311+G(3df)) accounts for the presence of a very weak band at 1780 cm −1 in the gas phase IR spectrum, which is consequently assigned to the ν(CO) of the anti form. On the other hand, the strongest absorption at 819 cm −1 in the IR spectra (gas) is assigned to the Cl− C−S antisymmetric stretching mode (ν as (Cl−C−S)) in comparison with IR spectra of related molecules such as ClC(O)SCl (818 cm −1 ).…”

Carbonyl Diisocyanate CO(NCO)2: Synthesis and Structures in Solid State and Gas Phase

“…The shortening of the central ∠(N 1 C 1 N 2 ) angle from the anti – anti to the syn – syn is a common feature with the F 2 NC­(O)­NCO (B3LYP/aug-cc-pVTZ) and the CO­(N 3 ) 2 (B3LYP/6–311+G­(3df)). This feature can be explained with by a resonance structure occurring within the NRT analysis.…”

Conformational Behavior of CH3OC(O)SX (X = CN and SCN) Pseudohalide Congeners. A Combined Experimental and Theoretical Study

“…The occurrence of two bands in the region of the CO group in the IR (gaseous an Ar matrix isolated) spectrum (Figure ) suggests that an equilibrium of two conformers in similar concentrations is present at room temperature. It is well-known that the ν(CO) normal mode of carbonyl compounds is very sensitive to conformational properties. , The carbonyl stretching region (1900−1700 cm −1 ) of the infrared spectra of CH 3 OC(O)SCN in the vapor phase and isolated in an Ar-matrix are shown in detail in Figure . Two intense absorptions are evident; one band in the gaseous spectrum occurs at 1794 cm −1 and the other at 1765 cm −1 .…”

“…The IR and Raman (liquid) spectra of CH 3 OC(O)SSCN are shown in Figure . A tentative assignment of the observed bands was carried out by comparison with calculated wavenumbers, as well as on comparison with spectra of related molecules. , Experimental and calculated [B3LYP/6-311++G**] frequencies, intensities, and their tentative assignments are given as Supporting Information (Table S1). C 1 symmetry is expected for the feasible rotamers of CH 3 OC(O)SSCN.…”