Experimental and theoretical vibrational study of 2,2,2-trifluoroethyl trifluoromethanesulfonate, CF3SO2OCH2CF3

Spectroscopic investigation of 4-nitro-3-(trifluoromethyl)aniline, NBO analysis with 4-nitro-3-(trichloromethyl)aniline and 4-nitro-3-(tribromomethyl)aniline

The Fourier transform infrared (FT-IR) and FT-Raman spectra of 4-nitro-3-(trifluoromethyl)aniline (NTFA) were recorded in the regions 4000-400 cm(-1) and 3500-100 cm(-1), respectively. Utilizing the observed FT-IR and FT-Raman data, a complete vibrational assignment and analysis of the fundamental modes of the compounds was carried out. Extensive studies on the vibrational, structural, thermodynamic characteristics as well as the electronic properties of NTFA were carried out using ab initio and DFT methods. In this kind of systems, the position of the substituent group in the benzene ring as well as its electron donor-acceptor capabilities play a very important role on the molecular and electronic properties. The values of the total dipole moment (μ) and the first order hyperpolarizability (β) were computed using B3LYP/6-311++G(d,p) and B3LYP/6-311G(d) calculations. The Mulliken's charges, the natural bonding orbital (NBO) analysis on 4-nitro-3-(trifluoromethyl)aniline, 4-nitro-3-(trichloromethyl)aniline and 4-nitro-3-tribromomethyl)aniline were carried out for various intramolecular interactions that are responsible for the stabilization of the molecule. Thermodynamic functions of the investigated molecule were also computed. The calculated HOMO-LUMO energies show that charge transfer occurs in the molecule. The influence of fluorine, amino and nitro group on the geometry of benzene and its normal modes of vibrations has also been discussed.

Vibrational spectroscopic, first-order hyperpolarizability and HOMO, LUMO studies of 4-chloro-2-(trifluoromethyl) aniline based on DFT calculations

The Fourier-transform infrared and FT-Raman spectra of 4-chloro-2-(trifluoromethyl) aniline (4C2TFA) were recorded in the region 4000-400 cm(-1) and 3500-50 cm(-1) respectively. Quantum chemical calculations of energies, geometrical structure and vibrational wavenumbers of 4C2TFA were carried out by density functional theory (DFT/B3LYP) method with 6-311+G(d,p) and 6-311++G(d,p) basis sets. The difference between the observed and scaled wavenumber values of most of the fundamentals is very small. The values of the total dipole moment (μ) and the first order hyperpolarizability (β) of the investigated compound were computed using B3LYP/6-311++G(d,p) calculations. The calculated results also show that 4C2TFA might have microscopic non-linear optical (NLO) behavior with non-zero values. A detailed interpretation of infrared and Raman spectra of 4C2TFA is also reported. The calculated HOMO-LUMO energy gap shows that charge transfer occurs within the molecule.

Conformational and vibrational analysis of methyl methanesulfonate, CH3SO2OCH3

The molecular structure of methyl methanesulfonate, CH(3)SO(2)OCH(3), has been optimized by using methods based on density functional theory, coupled cluster, and Moller-Plesset second order perturbation theory (MP2). With regard to CH(3)SO(2)OCH(3), two populated conformations with symmetries C(s) and C(1) are obtained, the former being more stable than the latter. The theoretical data indicate that although both anti and gauche conformers are possible by rotation about the S-O bond, the preferred conformation is anti. The total energy as a function of the CSOC dihedral angle has been calculated using the MP2 method with the 6-31G(d) and cc-pVDZ basis sets and the hybrid functional B3LYP using 6-31G(d), 6-311G(d,p), and 6-311++G(d,p) basis sets. A natural bond orbital analysis showed that the lone pair --> sigma* hyperconjugative interactions favor the anti conformation. Furthermore, the infrared spectra for the liquid and solid phases, the Raman spectrum for the liquid one, and the inelastic neutron scattering spectrum of the solid phase have been recorded, and the observed bands have been assigned to the vibrational modes. The experimental vibrational data, along with calculated theoretical force constants, were used to define a scaled quantum mechanical force field for the target system that enabled us to fit the measured frequencies with a final root-mean-square deviation of 10 cm(-1).

Simulation of IR and Raman spectral based on scaled DFT force fields: a case study of 2-amino 4-hydroxy 6-trifluoromethylpyrimidine, with emphasis on band assignment

This work deals with the vibrational spectroscopy of 2-amino 4-hydroxy 6-triflouromethylpyrimidine (AHFMP) by means of quantum chemical calculations. The mid and far FTIR and FT-Raman spectra were measured in the condensed state. The fundamental vibrational frequencies and intensity of vibrational bands were evaluated using density functional theory (DFT) with the standard B3LYP/6-31G* and B3LYP/6-311+G** method and basic set combinations. Normal co-ordinate calculations were performed with the DFT force field corrected by a recommended set of scaling factors yielding fairly good agreement between observed and calculated frequencies. Simulation of infrared and Raman spectra utilizing the results of these calculations led to excellent overall agreement with the observed spectral patterns. The SQM approach applying selective scaling of the DFT force field was shown to be superior to the uniform scaling method in its ability to allow for making modifications in the band assignment, resulting in more accurate simulation of IR and Raman Spectra.

Gas-Phase Structure, Rotational Barrier, and Vibrational Properties of Methyl Methanethiosulfonate, CH3SO2SCH3: An Experimental and Computational Study

The molecular structure of methyl methanethiosulfonate, CH3SO2SCH3, has been determined in the gas phase from electron-diffraction data supplemented by ab initio (HF, MP2) and density functional theory (DFT) calculations using 6-31G(d), 6-311++G(d,p), and 6-311G(3df,3pd) basis sets. Both experimental and theoretical data indicate that although both anti and gauche conformers are possible by rotating about the S-S bond, the preferred conformation is gauche. The barrier to internal rotation in the CSSC skeleton has been calculated using the RHF/6-31G(d), MP2/6-31G(d), and B3LYP/6-31G(d) methods as well as MP2 with a 6-31G(3df) basis set on sulfur and 6-31G(d) on C, H, and O. A 6-fold decomposition of the rotational barrier has been performed in terms of a Fourier-type expansion, enabling us to analyze the nature of the potential function, showing that the coefficients V1 and V2 are the dominant terms; V1 is associated with nonbonding interactions, and V2 is associated with hyperconjugative interactions. A natural bond orbital analysis showed that the lone pair --> sigma* hyperconjugative interactions favor the gauche conformation. Furthermore, the infrared spectra for the liquid and solid phases and the Raman spectrum for the liquid have been recorded, and the observed bands have been assigned to the vibrational normal modes. The experimental vibrational data, along with calculated theoretical force constants, were used to define a scaled quantum mechanical force field for the target system that enabled us to estimate the measured frequencies with a final root-mean-square deviation of 6 cm-1.

Theoretical Structure and Vibrational Analysis of Ethyl Methanesulfonate, CH3SO2OCH2CH3

Ethyl methanesulfonate, CH3SO2OCH2CH3, is well-known as an alkylating agent in mutagenic and carcinogenic processes. Its electronic structure and that of the methanesulfonate anion (CH3SO3-) were determined using optimization methods based on density functional theory and Moller-Plesset second-order perturbation theory. For CH3SO2OCH2CH3, two conformations with symmetries C(s) and C1 are obtained, the former being more stable than the latter. Natural bond orbital (NBO) calculations show the C(s) conformation provides a more favorable geometry of the lone pairs of the oxygen atom linking the ethyl group. The NBO technique also reveals the characteristics of the methanesulfonate anion as a leaving group due to the rearrangement of the excess electronic charge after alkylation. Furthermore, the infrared spectra of CH3SO2OCH2CH3 are reported for the liquid and solid states as well as the Raman spectrum of the liquid. Comparison to experiment of the conformationally averaged IR spectrum of C(s) and C1 provides evidence of the predicted conformations in the solid IR spectrum. These experimental data along with the calculated theoretical force constants are used to define a scaled quantum mechanical force field for the target molecule, which allowed the measured frequencies to be reproduced with a final root-mean-square deviation of 9 cm(-1) and, thus, a reliable assignment of the vibrational spectrum.

Infrared and Raman spectra and quantum chemistry calculations for 2,2,2-trifluoroethyl trichloromethanesulfonate, CCl3SO2OCH2CF3

The infrared spectra of CCl3SO2OCH2CF3 were obtained in the gaseous, liquid and solid states and complemented with the Raman spectrum of the liquid. Quantum chemistry calculations using the density functional theory (DFT) were used to predict the most stable geometry and conformation of the studied molecule. The harmonic vibrational frequencies and force field were also calculated. Comparison with related molecules and with the predicted frequencies was used as the basis for the assignment of the observed spectral features. Subsequently, a scaling of the original force field by means of a least square procedure was made in order to reproduce as well as possible the experimental frequencies, leading to a final root mean square deviation of 10.6 cm(-1).