Infrared, Raman spectra and DFT calculations of chlorine substituted anilines (original) (raw)
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The structure of aniline was studied by semiempirical, ab initio, and density functional methods. Complete geometry optimization of the minimum energy structure and of the transition states for internal rotation and inversion of the amino group was carried out using several levels. The performance of the different methods in calculating and describing the vibrational frequencies of aniline was determined. The normal modes were characterized by the magnitudes and direction of the displacement vectors. Three procedures were used to obtain the scaled frequencies, two of them new, using specific scale factors and scaling equations from the benzene molecule. The errors obtained were compared with those calculated through other standard procedures. A reassignment of several bands was made. A comparison of the cost-effective method and procedure of scaling was carried out.
The Journal of Chemical Physics, 2003
Comprehensive studies of the molecular and electronic structures, vibrational frequencies, and infrared and Raman intensities of the aniline radical cation, C 6 H 5 NH 2 ϩ have been performed by using the unrestricted density functional ͑UB3LYP͒ and second-order Møller-Plesset ͑UMP2͒ methods with the extended 6-311ϩϩG͑df,pd͒ basis set. For comparison, analogous calculations were carried out for the closed-shell neutral aniline. The studies provided detailed insight into the bonding changes that take place in aniline upon ionization. The natural bond orbital ͑NBO͒ analysis has revealed that the p-radical conjugative interactions are of prime importance in stabilizing the planar, quinoid-type structure of the aniline radical cation. It is shown that the natural charges calculated for aniline are consistent with the chemical properties of this molecule ͑an ortho-and para-directing power of the NH 2 group in electrophilic substitutions͒, whereas Mulliken charges are not reliable. The theoretical vibrational frequencies of aniline, calculated by the B3LYP method, show excellent agreement with the available experimental data. In contrast, the MP2 method is deficient in predicting the frequencies of several modes in aniline, despite the use of the extended basis set in calculations. The frequencies of aniline radical cation, calculated at the UB3LYP/ 6-311ϩϩG͑df,pd͒ level, are in very good agreement with the recently reported experimental data from zero kinetic energy photoelectron and infrared depletion spectroscopic studies. The clear-cut assignment of the IR and Raman spectra of the investigated molecules has been made on the basis of the calculated potential energy distributions. Several bands in the spectra have been reassigned. It is shown that ionization of aniline can be easily identified by the appearance of the very strong band at about 1490 cm Ϫ1 , in the Raman spectrum. The redshift of the N-H stretching frequencies and the blueshift of the C-H stretching frequencies are observed in aniline, upon ionization. As revealed by NBO analysis, the frequency shifts can be correlated with the increase of electron density ͑ED͒ on the antibonding orbitals ( NH * ) and decrease of ED on CH * , respectively. These effects are associated with a weakening of N-H bonds and strengthening of C-H bonds in the aniline radical cation. The simulated theoretical Raman and infrared spectra of aniline and its radical cation, reported in this work, can be used in further spectroscopic studies of their van der Waals clusters and hydrogen bonded complexes.
Accurate scaling of the vibrational spectra of aniline and several derivatives
The structure of aniline was studied by quantum chemical methods. Complete geometry optimization of the minimum energy structure and of the transition states for internal rotation and inversion of the amino group was carried out using several levels. The performance of the different methods in calculating and describing the vibrational wavenumbers of aniline was determined. The normal modes were characterized by the magnitude and direction of the displacement vectors. Three procedures were used to obtain the scaled wavenumbers, two of them new, using specific scale factors and scaling equations from benzene molecule. The errors obtained were compared with those calculated through other standard procedures. A reassignment of several bands was made. A comparison of the cost/effective method and procedure of scaling was carried out. Specific scale factors and scale equations were determined for the amino group to be used in large aromatic amines. q
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2009
In this work, the experimental and theoretical vibrational spectra of 2-chloro-4-methylaniline (2Cl4MA, C 7 H 8 NCl) were studied. FT-IR and FT-Raman spectra of 2Cl4MA in the liquid phase have been recorded in the region 4000-400 cm −1 and 3500-50 cm −1 , respectively. The structural and spectroscopic data of the molecule in the ground state have been calculated by using Hartree-Fock (HF) and density functional method (B3LYP) with the 6-31G(d), 6-31G(d,p), 6-31+G(d,p), 6-31++G(d,p) and 6-311G(d), 6-311G(d,p), 6-311+G(d,p), 6-311++G(d,p) basis sets. The vibrational frequencies have been calculated and scaled values have been compared with experimental FT-IR and FT-Raman spectra. The observed and calculated frequencies are found to be in good agreement. The complete assignments were performed on the basis of the total energy distribution (TED) of the vibrational modes, calculated with scaled quantum mechanics (SQM) method. The DFT-B3LYP/6-311++G(d,p) calculations have been found more reliable than the ab initio HF/6-311++G(d,p) calculations for the vibrational study of 2Cl4MA. The optimized geometric parameters (bond lengths and bond angles) were compared with experimental values of aniline and p-methylaniline molecules.
Journal of Molecular Structure
In this work, the experimental and theoretical vibrational spectra of 2-chloro-5-methylaniline (2Cl5MA, C 7 H 8 NCl) were studied. FT-IR and FT-Raman spectra of 2Cl5MA in the liquid phase were recorded in the region 4000-400 cm À1 and 3500-50 cm À1 , respectively. The structural and spectroscopic data of the molecule in the ground state were calculated by using Hartree-Fock and density functional method (B3LYP) with the 6-31G(d), 6-31G(d,p), 6-31+G(d,p), 6-31++G(d,p), 6-311G(d), 6-311G(d,p), 6-311+G(d,p) and 6-311++G(d,p) basis sets. The vibrational frequencies were calculated and scaled values were compared with experimental FT-IR and FT-Raman spectra. The observed and calculated frequencies are found to be in good agreement. The complete assignments were performed on the basis of the total energy distribution (TED) of the vibrational modes, calculated with scaled quantum mechanics (SQM) method. The optimized geometric parameters (bond lengths and bond angles) were compared with experimental values of aniline and p-methyl aniline molecules.
Journal of Physical Organic Chemistry
In this work, the experimental and theoretical vibrational spectra of N1-methyl-2-chloroaniline (C 7 H 8 NCl) were studied. FT-IR and FT-Raman spectra of the title molecule in the liquid phase were recorded in the region 4000-400 cm S1 and 3500-50 cm S1 , respectively. The structural and spectroscopic data of the molecule in the ground state were calculated by using density functional method (B3LYP) with the 6-311RRG(d,p) basis set. The vibrational frequencies were calculated and scaled values were compared with experimental FT-IR and FT-Raman spectra. The observed and calculated frequencies are found to be in good agreement. The complete assignments were performed on the basis of the total energy distribution (TED) of the vibrational modes, calculated with scaled quantum mechanics (SQM) method. 13 C and 1 H NMR chemical shifts results were compared with the experimental values. The optimized geometric parameters (bond lengths and bond angles) were given and are in agreement with the corresponding experimental values of aniline and p-methyl aniline.
In this study, 4-Methoxy-N-(3-phenylallylidene) aniline has been synthesized and characterized by FTIR and NMR spectroscopic techniques. The optimized geometrical structure, vibrational frequencies and NMR shifts of title molecule were obtained by using ab initio HF and density functional method (B3LYP) with 6-31G* basis set. The experimental and calculated geometrical parameters were compared with each other. The calculated infrared (IR) and NMR data were compared with experimental values using HF and B3LYP/6-31G* level of theory. It was found to be a good correlation between experimental and calculated data. In addition, HOMO and LUMO analysis of title molecule were calculated using corresponding methods with 6-31G* basis set. The calculated HOMO-LUMO energies were used to calculate some properties of title molecule.
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2011
Quantum chemical calculations of energies, geometrical structural parameters, harmonic and anharmonic frequencies of 2,4-DCP and 4,6-DCP were carried out by HF and density functional theory methods with 6-311++G(d,p) as basis set. The assignment of each normal mode has been made using the observed and calculated frequencies, their IR and Raman intensities. A detailed interpretation of the FT-IR and FT-Raman spectra of 2,4-DCP and 4,6-DCP was reported on the basis of the calculated potential energy distribution (PED). A comparison of theoretically calculated vibrational frequencies at B3LYP/6-311++G(d,p) with FT-IR and FT-Raman experimental data shows good agreement between them. Natural atomic charges of 2,4-DCP and 4,6-DCP were calculated and compared with pyrimidine molecule.
Theoretical structural analysis of 3-CHLORO-4-FLUORO-ANILINE
Journal of Physical and Theoretical Chemistry, 2019
This study was designed to compute the spectroscopic properties of aniline family, and educates the 3chloro-4-fluoro-aniline, which have unique pharmaceutical important. The structural and spectroscopic properties were investigated using a quantum calculation. The density functional theory approach at B3LYP/6–31G (d) data set is apply. IR and UV-Visible spectrophotometric estimated through GAMESS, Raman spectrogram was obtain through Gaussian and NMR C 1 and C13 spectrums were also predicted through computational methods. After obtaining the results, they were tabulated. The results of current computational analysis is in sense useful to predict even a complex aniline precursor and advantage of the current computational strategy is beneficial for other aniline molecules containing chlorine and fluorine atoms. The success of this Density function theoretical results opens a pathway to apply a correct algorithm and a force field for the assignments of aniline family spectroscopy property.