Infrared and Raman spectra of 4-(dimethylamino)benzonitrile and isotopomers in the ground state and vibrational analysis

473

114

NIR-FT Raman and FT-IR spectra of the crystallized 2,6-bis (p-N,N-dimethyl benzylidene)cyclohexanone (C 24 H 28 N 2 O) have been recorded in the region 3200-500 and 4000-400 cm −1 , respectively. The spectral interpretation has been done following full structure optimization and vibrational wavenumber calculations based on the density functional theory (DFT) using the standard B3LYP/6-31G * basis set. The predicted vibrational spectra are in excellent agreement with the experiment, permitting an unambiguous assignment for the unusual downshifting of nC O caused by expanded conjugation effects in the dienone system. The optimized geometry clearly demonstrates the 'half-chair' conformation of the central nonheterocyclic ring. The ring C-H stretching vibrational modes involving aromatic hydrogen atoms participating in steric interaction have been observed with low intensities. There are valid structural and spectral bases for the enhancement of its bioactivity due to full charge transfer reaction by the substitution of the electron-donating 4-dimethylamino group into the aryl rings. The existence of intramolecular, C-H ... O, improper, blue-shifted hydrogen bond was investigated by means of the natural bonding orbitals (NBO) analysis. There are also slight dissimilarities in the bond lengths and endocyclic bond angles of both phenyl rings due to the effect of the heavy substitution. The characteristic ring modes have also been assigned in detail.

Section: Dimethylamino Vibrationsmentioning

confidence: 99%

Structural conformation and vibrational spectroscopic studies of 2,6‐bis(p‐N,N‐dimethyl benzylidene)cyclohexanone using density functional theory

James¹,

Raj

Reghunathan

et al. 2006

473

114

“…[42] The n − π conjugation between the nitrogen lone pair electrons of the substituents and the phenyl ring π -system is strong in the ground state, as indicated by the Ph-N wavenumber 1377 cm −1 . [43,44] The Ph-N (C-N) stretching wavenumber of AZAC is observed as very strong bands both in IR and Raman at 1396 cm −1 , which is upshifted by 19 cm −1 because of strong conjugation. This is well reflected in the NBO analysis results given in Table S2 (Supporting Information), as the energies of hyperconjugative interactions LP N 8 → π * C 3 -C 4 and LP N 30 → π * C 25 -C 26 become strong as 160.09 and 152.88 kJ/mol, respectively.…”

Section: Dimethylamino Vibrationsmentioning

confidence: 99%

Azure A chloride: computational and spectroscopic study

Snehalatha¹,

Joe²,

Ravikumar³

et al. 2008

Fourier transform Raman and IR as well as UV-visible spectra of the phenothiazine dye Azure A chloride, 3-amino-7-(dimethylamino) phenothiazin-5-ium chloride were recorded and analyzed. The spectral interpretation was done following full structure optimization and vibrational wavenumber calculations based on the density functional theory (DFT) using the standard B3LYP/6-31G(d) basis set. The N-H stretching wavenumber is found to be lowered owing to intermolecular N-H· · ·S hydrogen bonding. The downshift of C-H stretching wavenumber is discussed. The first hyperpolarizability of the dye is calculated. Time-dependent density functional theory (TD-DFT) calculations of electronic spectra were performed on the optimized structure and compared with the experimental UV-visible spectrum. The atomic net charges of the molecule reveal the -M effect of the nitrogen atoms in the molecule. Stability of the molecule arising from hyperconjugative interactions leading to its nonlinearity and bioactivity, charge delocalization and mesomeric effects have been analyzed using natural bond orbital (NBO) analysis.

“…Moreover, a detailed theoretical or experimental vibrational analysis on 4ABN has not been reported yet, although several accurate studies by IR and Raman spectroscopy have been reported. 59 Therefore, the present investigation was undertaken to study the vibrational spectra of this important molecule completely and to identify the various normal modes of vibration with the help of density functional calculations (DFT).…”

Section: Introductionmentioning

confidence: 99%

4‐Aminobenzonitrile: ab initio calculations, FTIR and Raman spectra

Palafox

Rastogi

Vats

2006

The experimental IR (in different matrices) and Raman spectra of 4-aminobenzonitrile molecule were recorded. The results were compared with theoretical values. Geometry, vibrational wavenumbers and thermodynamic parameters were calculated using DFT quantum chemical methods. With the help of specific scaling procedures, the experimentally observed FTIR and Raman vibrational wavenumbers were analyzed and assigned to different normal modes of the molecule. The error obtained was, in general, very low. The contributions of the different modes to each wavenumber were determined using potential energy distributions (PEDs). Other general conclusions were also deduced.