Jayashree Yenagi

Vibrational assignments for 7-methyl-4-bromomethylcoumarin, as aided by RHF and B3LYP/6-31G* calculations.

Infrared (4000-400 cm(-1)) and Raman (3500-50 cm(-1)) spectral measurements have been made for the solid sample of 7-methyl-4-bromomethylcoumarin. Electronic structure calculations at RHF/6-31G* and B3LYP/6-31G* levels of theory have been performed, giving equilibrium geometries, harmonic vibrational spectra and normal modes. Different orientations of bromomethyl group have yielded only two conformers, of which the most stable one lying lower from the other conformer by approximately 7.99 kJ/mol, is non-planar with no symmetry. A complete assignment of the vibrational modes, aided by the calculations, has been proposed. Coupled vibrations are manifest in many modes. Some spectral features, compared to 6-methyl-4-bromomethylcoumarin, show changes across both IR and Raman spectra, involving mainly skeletal vibrations, and to a lesser degree, methyl and bromomethyl vibrations. Low-frequency vibrations below 150 cm(-1) are assigned to lattice modes.

Vibrational spectra, normal modes, ab initio and DFT calculations for 6-Chloro- and 7-Chloro-4-bromomethylcoumarins.

Vibration spectral measurements - Infrared (4000-400 cm(-1)) and Raman (3500-50 cm(-1)) spectra - have been made for the solid samples of 6-Chloro- and 7-Chloro-4-bromomethylcoumarins. Ground electronic state energies, equilibrium geometries, harmonic vibrational spectra and normal modes have been computed using ab initio - RHF/6-31G* - and DFT - B3LYP/6-31G* levels of theory. The optimization yielded three structures for each molecule, with one being a transition state structure. Of the remaining two conformers, one belongs to C(s) symmetry and the other belongs to C(1), the latter being the most stable one. The optimized dihedral angle for -CH(2)Br group is 111 degrees in agreement with X-ray diffraction results reported for the similar molecular systems. Assignment of all the observed spectral bands has been proposed. The absorptions show band pattern revealing isomer characteristics and vibrational coupling in varying degrees; the Raman spectra show structural changes associated with the rings as well as lattice modes.

Ab initio/DFT electronic structure calculations, spectroscopic studies and normal coordinate analysis of 2-chloro-5-bromopyridine.

FT-IR (4000-400 cm(-1)) and FT-Raman (3500-50 cm(-1)) spectral measurements of solid sample of 2-chloro-5-bromopyridine have been done. Ab initio and DFT calculations have been performed giving energies, optimized structures, harmonic vibrational frequencies, depolarization ratios, IR intensities, Raman activities and atomic displacements. Furthermore, force field calculations have been performed by normal coordinate analysis. A complete assignment of the observed spectra, based on spectral correlations, electronic structure calculations and normal coordinate analysis, has been proposed. The results of the calculations have been used to simulate IR and Raman spectra for the molecule that showed good agreement with the observed spectra. The SQM method, which implies multiple scaling of the DFT force fields, has been shown superior to the uniform scaling approach. The energy and oscillator strength calculated by Time-dependent DFT results are in good agreement with the experimental results.

Identification of mineral compositions in some renal calculi by FT Raman and IR spectral analysis

We present in this paper accurate and reliable Raman and IR spectral identification of mineral constituents in nine samples of renal calculi (kidney stones) removed from patients suffering from nephrolithiasis. The identified mineral components include Calcium Oxalate Monohydrate (COM, whewellite), Calcium Oxalate Dihydrate (COD, weddellite), Magnesium Ammonium Phosphate Hexahydrate (MAPH, struvite), Calcium Hydrogen Phosphate Dihydrate (CHPD, brushite), Pentacalcium Hydroxy Triphosphate (PCHT, hydroxyapatite) and Uric Acid (UA). The identification is based on a satisfactory assignment of all the observed IR and Raman bands (3500-400c m(-1)) to chemical functional groups of mineral components in the samples, aided by spectral analysis of pure materials of COM, MAPH, CHPD and UA. It is found that the eight samples are composed of COM as the common component, the other mineral species as common components are: MAPH in five samples, PCHT in three samples, COD in three samples, UA in three samples and CHPD in two samples. One sample is wholly composed of UA as a single component; this inference is supported by the good agreement between ab initio density functional theoretical spectra and experimental spectral measurements of both sample and pure material. A combined application of Raman and IR techniques has shown that, where the IR is ambiguous, the Raman analysis can differentiate COD from COM and PCHT from MAPH.

Effect of nitro groups on the photo physical properties of benzimidazolone: A solvatochromic study

Electronic absorption and fluorescence spectra of mono, di, and tri-nitro benzimidazolones are measured at room temperature (298 K) in nine solvents with different polarities and the observed shifts are compared with benzimidazolone. Ground and excited state electric dipole moments are determined using the solvatochromic method based on the bulk solvent properties, F(1)(ε, n) and F(2)(ε, n). A reasonable agreement is observed between the experimental and ab initio dipole moments. Change in dipole moment is also determined using the solvatochromic method based on the microscopic solvent polarity parameter, (E(T)(N)), which considers the polarization changes due to hydrogen bonding in different solvents. It has been observed that the correlation of the solvatochromic Stokes shifts with the parameter (E(T)(N)), is superior to that derived using bulk solvent polarity functions for all the benzimidazolones reported in the present study. Calculated difference between excited state and ground state dipole moments seems to be a good measure of the effect of nitro group when correlated with (E(T)(N)).

Cyclopropanes in water: a diastereoselective synthesis of substituted 2H-chromen-2-one and quinolin-2(1H)-one linked cyclopropanes

A one-pot three component reaction has been developed for the synthesis of substituted cyclopropanes employing 4-bromomethyl-2H-chromen-2-one/quinolin-2(1H)-ones, aromatic aldehydes and activated nitriles. The room temperature reaction in aqueous medium has been found to be diastereoselective and high yielding.

Vibrational and ab initio studies of 3-acetyl-6-bromocoumarin and 3-acetyl-6-methylcoumarin

Infrared absorption and Raman spectra (3500-50 cm(-1)) of 3-acetyl-6-bromocoumarin and 3-acetyl-6-methylcoumarin have been measured and interpreted, aided by electronic structure calculations at RHF and B3LYP using 6-31(d, p) basis set. It has been determined that the rotation of the acetyl group with respect to the coumarin ring results in three conformers--two trans and one cis--for each molecule, with one trans conformer being the most stable in both cases. There are significant changes in the vibrational structure as characterized by positions and intensities of certain modes in going from 3-acetyl-6-bromocoumarin to 3-acetyl-6-methylcoumarin. The carbonyl stretching mode of the pyrone ring is stable in both molecules whereas the same mode in acetyl groups is not. Ring stretching vibrations are coupled to C-H in-plane bending vibrations. Down-shifting of frequencies of methyl vibrations in acetyl group occurs vis-à-vis methyl vibrations in 3-acetyl-6-methylcoumarin. A strong Raman band at 126 cm(-1) in both molecules is structure-independent non-genuine mode, correlated to lattice vibrations in the solid phase.

Hydrogen bond, dimerization and vibrational modes in 2-chloro-3-hydroxybenzaldehyde and 3-chloro-4-hydroxybenzaldehyde from vibrational and ab initio studies

Ab initio conformers and dimers have been computed at RHF and B3LYP/6-31G* levels for isomers 2-chloro-3-hydroxybenzaldehyde and 3-chloro-4-hydroxybenzaldehyde to explain the observed infrared absorption and Raman vibrational spectral features in the region 3500-50 cm(-1). The position of the chlorine in ortho position with respect to aldehyde group in 2-chloro-3-hydroxybenzaldehyde yields four distinct conformers; whereas the chlorine in meta position in 3-chloro-4-hydroxybenzaldehyde yields effectively only three conformers. Major spectral features as strong absorptions near 3160-80 cm(-1), down-shifting of the aldehydic carbonyl stretching mode and up-shifting of hydroxyl groups in-plane bending mode are explained using ab initio evidence of O-H⋯O bond-aided dimerization between the most stable conformers of each molecule. Absorption width of about 700 cm(-1) (∼8.28 kJ/mol) of O-H stretching modes suggests a strong hydrogen bonding with the ab initio bond lengths, O-H⋯O in the range of 2.873-2.832 Å. A strong Raman mode near 110-85 cm(-1) in each molecule is interpreted to be coupled vibrations of pseudo-dimeric trans and cis structures.

A study of hydrogen bonded vibrational spectra of (R)-(+)-Methylsuccinic acid, as aided by DFT dimer analysis.

Infrared and Raman spectral measurements in the region 4000-400cm(-1) have been carried out for (R)-(+)-Methylsuccinic acid. The vibrational band structures near 3100-3040cm(-1) in the IR and near 1650cm(-1) in the Raman spectra have indicated the presence of an inter-molecular hydrogen bonding. A DFT dimer model has been proposed that involves O-H⋯OC type of hydrogen bonding. The proposed dimer model has been derived from the three stable monomers computed at RHF/3-21G and B3LYP/6-311+G(d,p) levels of theory. A total of six dimer structures have been considered with a Boltzmann population of 38% for the most stable dimer and 62% for the remaining five dimer populations. A Boltzmann population weighted vibration spectrum has predicted bands, among others, for O-H⋯OC group that are in very good agreement with experiment. All the dimers have the same structure in that the two pairs of -O-H and -OC form a closed cyclic structure with a local center of inversion. This dimer geometry has given rise to one asymmetric mode at 1683 and one symmetric -CO mode at 1637cm(-1) corresponding to mutually exclusive an experimental IR band at 1700 and a Raman band at 1651cm(-1). Further, the bond length, H⋯O, for the most stable dimer is 1.686Å, being shorter than the sums of van der Waals radii, 2.72Å and the angle between O-H and H⋯O is almost linear (179°) suggesting that the hydrogen bonding is fairly strong.

(R)-(-)-2-Pyrrolidinemethanol: A combined experimental and DFT vibrational analysis of monomers, dimers and hydrogen bonding.

Experimental IR and solution phase spectra of (R)-(-)-2-Pyrrolidinemethanol showing evidence of hydrogen bonding have been interpreted by computing vibrational modes of monomers and dimers with the molecular species due to intra- and inter-molecular hydrogen bonding, at B3LYP/6-311+G(d,p) level density functional theoretical calculations. Computed vibrational frequencies of Boltzmann population-weighted dimers for stretching and bending of O-H and N-H modes associated with the inter-molecular N-H⋯O and O-H⋯O hydrogen bonding are in good agreement with the measured IR absorption, Raman and solution-phase IR values near 3289 cm(-1), 3450 cm(-1) and 1400-1300 cm(-1). Further, the H⋯O length is shorter in O-H⋯O than in N-H⋯O by ∼10% suggesting that O-H⋯O is a stronger bond. While the solution-phase IR spectral features suggest strong inter-molecular associations, it is short of demonstrating which type of bonding is dominant factor. We conclude that the measured IR, Raman and solution-phase IR spectral features indicate the presence of both types of hydrogen bonds.