Vibrational spectroscopy of lapachol, α- and β-lapachone: Theoretical and experimental elucidation of the Raman and infrared spectra

Raman and infrared spectroscopy were applied for the vibrational characterization of lapachol and its pyran derivatives, α-lapachone and β-lapachone. Experimental spectra of solid state samples were acquired between 4000 and 100 cm⁻¹ in Raman experiments, and between 4000 and 600 cm⁻¹ (mid-infrared) and 600–100 cm⁻¹ (far-infrared) with FTIR spectroscopy, respectively. Full structure optimization and theoretical vibrational wavenumbers were calculated at the B3LYP/6-31 + + G(d,p) level. Detailed assignments of vibrational modes in an experimental and theoretical spectra were based on potential energy distribution analyses, using Veda 4.1 software. Clear differentiation between the three compounds was verified in the region between 1725 and 1525 cm⁻¹, in which the ν(CO) and ν(CC) modes of the quinone moiety were assigned.     

Vibrational spectra and intermolecular potential of the α-form crystal of glycine

Polarized Raman and far i.r. spectra of glycine and N-deuterated glycine crystallized in the α-form were recorded. The normal coordinate analysis of the optical active intra- and intermolecular vibrations of the α-form crystal of glycine was carried out. A modified Urey—Bradley type intramolecular potential was adopted. The observed factor group splittings were elucidated fairly well by using the intermolecular potential including the exchange repulsion—dispersion interaction between non-bonded atoms and the Coulomb interaction. The stretching potential for the hydrogen bonds was found to contribute appreciably to the lattice frequencies.     

Vibrational spectra of 1,1-dichloroethanes and βCH stretching interaction force constants

Infrared and Raman spectra are described and assignments are reported for CH₃CDCl₂ and CD₃CHCl₂, together with new i.r. data for CH₃CHCl₂ and CD₂HCHCl₂. Using previously obtained “isolated” CH stretching frequencies, the above data enable the trans and gauche stretch—stretch interaction force constants to be determined:f′_g = ±0.011, f′_t = ∓0.026 mdyn/Å. Similar values, f′_g = +0.016, f′_t = −0.029, may be obtained from the earlier spectra of CHD₂CHD₂ due to Van Riet.The relations between the fundamental deformation bands and their overtones and combinations are examined in order to estimate the accuracy of predictions of v_s (=v₃) for the CH₃ and CD₃ groups from the 4 × 4 refinement and frequency sum rule. The data can be interpreted so as to give good agreement on the values of v^O_s of 2920 cm⁻¹ (CH₃) and 2115 cm⁻¹ (CD₃), provided that there are significance resonance shifts on both 2δ_a and 2δ′_s levels. That this is the case seems to be true for the CD₃ group, but is uncertain for the CH₃ one.     

Hydrogen bonding interactions between α-, β-glucose,and methacrylic acid

Intermolecular interactions between α-, β-glucose, and methacrylic acid (MAA) have been investigated. Twenty-two possible conformations have been optimized at the DFT(B3LYP) level of theory with the 6-31G(d) basis set. The geometrical parameters for the most stable configurations of hydrogen bonding sites in the optimized systems have been determined. The binding energies ΔE _bind have been calculated at the MP2/6-311++G(d,p) level of approximation taking into account the basis set superposition error (BSSE) and the zero-point vibrational energies corrections. Results indicate that the most stabilized complexes form hydrogen bonds either through carboxylic and hemiacetal oxygen atoms acting as proton acceptors. Both, α- and β-anomers are studied in the pyranose six-membered ring. In all complexes, the nuclear quadrupole coupling constants (χ) for ¹⁷O nuclei were obtained about 10.0 MHz, while for the ²H atoms they vary from ≈200.0 to ≈350.0 kHz.     

Study of α- and β-relaxation processes in supercooled sucrose liquids

The relaxation map of highly concentrated sucrose water mixtures was built using mechanical and impedance spectroscopies. Data of - and -relaxation processes obtained with both techniques complete calorimetric and rheological measurements. The temperature evolutions of the relaxations were extrapolated using the measured data and the equations commonly used to describe the relaxations: Arrhenius and WLF behaviours for respectively the - and -relaxations. The temperature/frequency domain when and processes merge for 99% sucrose solution is discussed with respect to scenery proposed in the literature.This revised version was published online in November 2005 with corrections to the Cover Date.     

Vibrational spectra of monosubstituted benzaldehydes—o-ethoxy-, p-ethoxy-, p-carboxy- and p-cyanobenzaldehydes

The i.r. spectra have been recorded for four monosubstituted benzaldehydes, namely o-ethoxy-, p-ethoxy-, p-carboxy- and p-cyanobenzaldehydes. Vibrational assignments are proposed.     

Electron momentum density and band structure calculations of α- and β-GeTe

We have measured isotropic experimental Compton profile of α-GeTe by employing high energy (662 keV) γ-radiation from a ¹³⁷Cs isotope. To compare our experiment, we have also computed energy bands, density of states, electron momentum densities and Compton profiles of α- and β-phases of GeTe using the linear combination of atomic orbitals method. The electron momentum density is found to play a major role in understanding the topology of bands in the vicinity of the Fermi level. It is seen that the density functional theory (DFT) with generalised gradient approximation is relatively in better agreement with the experiment than the local density approximation and hybrid Hartree–Fock/DFT.     

Ultraviolet absorption spectra of α-nitroso β-naphthol and its copper chelate

From a comparative study of the U.V. absorption spectra of α-nitroso-β-naphthol and of β-naphthol in neutral ethanol and in the presence of 0.1N HClO₄ and 0.1N KOH respectively, evidence in favour of the quinone-oxime structure of α-nitroso-β-naphthol has been presented. The spectrum of the copper chelate of α-nitroso-β-naphthol indicates a planar configuration of the complex with considerable resonance between the quinonoid and benzenoid structures of the ligand.     

Vibrational analysis of sodium α-, β- and γ-hydroxybutyrates. Inter- and intramolecular hydrogen bonds

The infrared and Raman spectra of sodium α-, β- and γ-hydroxybutyrates and their deuterated analogues are examined in the 4000-100 cm⁻¹ range and an assignment of the fundamental vibrations is given. Based on the localization of the asymmetric stretching vibrations ν_asOH and the out-of-plane vibration γOH, inter- and/or intramolecularly hydrogen-bonded forms are proposed: the low frequencies of ν_asOH (<3200 cm⁻¹) and high frequencies of γOH (≈800 cm⁻¹) argue in favour of the existence of intramolecular hydrogen bonding. Sodium α-hydroxybutyrate exhibits as a chelate ring with an intramolecular hydrogen bond between hydroxyl and carboxyl groups, whereas sodium, β-hydroxybutyrate has the two association forms with inter- and intramolecular hydrogen bonds. Sodium γ-hydroxybutyrate exists as a hydrogen-bonded polymer, with an intermolecular hydrogen bond between the hydroxyl groups and between the hydroxyl and carbonyl groups. At a crystallization temperature above 50°C, only the α- salt showed a structural change indicating the existence of intra- and intermolecular hydrogen bonds. This result is confirmed by differential scanning analysis.     

Ring-expanded bicyclic β-lactams: a structure-chiroptical properties relationship investigation by experiment and calculations

In the present work, the validity of the helicity rule relating the absolute configuration of the bridgehead carbon atom in bicyclic β-lactams to the sign of the 220 nm band observed in their electronic circular dichroism (ECD) spectra is examined for ring-expanded cephalosporin analogues. To this end, a series of model compounds with a seven-membered ring condensed with the β-lactam unit was synthesized. A key step of their synthesis was either the ring-closing metathesis (RCM) or the free radical cyclization leading to the seven-membered ring with an S, O, or C atom at the 6 position in the bicyclic skeleton. To investigate the scope and limitations of the simple, empirically established helicity rule, a combination of ECD spectroscopy, variable-temperature ECD measurements, X-ray analysis, and time-dependent density functional theory (TD-DFT) calculations was used. A comparison of the experimental ECD spectra with the spectra simulated by TD-DFT calculations gives a reasonable interpretation of the Cotton effects observed in the 240-215 nm spectral range. The results suggest that the helicity rule does not apply to the investigated compounds because of the planarity of their amide chromophore. Thus, these compounds do not constitute an exception to the rule that was established for bi- and polycyclic β-lactams with the nonplanar amide chromophore only.     

Syntheses of carbocyclic analogues of α-D-glucosamine, α-D-mannose, α-D-mannuronic acid, β-L-idosamine, and β-L-gulose

A versatile synthesis of orthogonally protected derivatives of carba-α-D-glucosamine, carba-α-D-mannose, carba-α-D-mannuronic acid, carba-β-L-idosamine, and carba-β-L-gulose from methyl α-D-mannoside is described. Our synthetic strategy utilizes the palladium-promoted Ferrier carbocyclization and persistent butane-2,3-diacetal protection to produce a key chiral cyclohexanone intermediate, from which all five carbasugar derivatives can readily be obtained.     

Some anomalies in the vibrational spectra of α, β-unsaturated ketones

Summary Some anomalies in the intensities of the bands of the C=C and C=O bonds in the vibrational spectra of , -unsaturated ketones have been explained by a difference in the sequence of the frequencies of the in-phase (_s) and out-of-phase (_as) vibrations of the multiple bonds in their cis (_s<_as) and trans (_s>_as) arrangements.     

Vibrational spectra of β-lactams—II. 1-Methyl-2-azetidinone and its deuterated compounds

The i.r. and Raman spectra of 1-methyl-2-azetidinone and its 3,3-d₂ and methyl-d₃ compounds have been recorded, and the observed bands have been assigned on the basis of the isotope effects and the normal coordinate analysis. Comparison of the CO and CN force constants between 2-azetidinone and 1-methyl-2-azetidinone indicates that, depending on amide resonance, these constants are related to each other. The solvent effects on the CO frequencies of four to seven-membered lactams have also been examined.     

Vibrational and thermodynamic properties of β-HMX: a first-principles investigation

Thermodynamic properties of β-HMX crystal are investigated using the quasi-harmonic approximation and density functional theory within the local density approximation (LDA), generalized gradient approximation (GGA), and GGA + empirical van der Waals (vdW) correction. It is found that GGA well describes the thermal expansion coefficient and heat capacity but fails to produce correct bulk modulus and equilibrium volume. The vdW correction improves the bulk modulus and volume, but worsens the thermal expansion coefficient and heat capacity. In contrast, LDA describes all thermodynamic properties with reasonable accuracy, and overall is a good exchange-correlation functional for β-HMX molecular crystal. The results also demonstrate significant contributions of phonons to the equation of state. The static calculation of equilibrium volume for β-HMX differs from the room-temperature value incorporating lattice vibrations by over 5%. Therefore, for molecular crystals, it is essential to include phonon contributions when calculated equation of state is compared with experimental data at ambient condition.     

Vibrational spectrum of α- and δ-TiCl3

The vibrational spectrum of α-TiCl₃ is assigned on the basis of a normal coordinate analysis. The i.r. bands shift to higher frequency from α- to δ-TiCl₃. This is discussed in terms of a dispersion relation for k_c in α-TiCl₃ and force constants, where the former is carried out for examining effect on disorder to the c axis in δ-TiCl₃. The shift is explained in terms of a change in force constants rather than disorder.     

Vibrational spectra of β-lactams—III. potassium 2-azetidinone-1-sulfonate and its isotopic compounds

The IR and Raman spectra of potassium 2-azetidinone-1-sulfonate and its three deuterated and two ¹⁵N-substituted compounds have been recorded, and the observed bands have been assigned on the basis of the isotope effects and the normal coordinate analysis. Comparison of the force constants for the amide group among 2-azetidinone, 1-methyl-2-azetidinone and potassium 2-azetidinone-1-sulfonate indicates that there is a correlation between these constants and the ease of hydrolysis which was determined by NMR spectroscopy, depending on the amide resonance.     

IR spectra of long-chain α,ω-alkanediols: 1,22-docosanediol and 1,44-tetratetracontanediol

The IR absorption spectra of α,ω-alkanediols with different chain lengths, HO(CH₂)₂₂OH and HO(CH₂)₄₄OH, in the spectral range of 400–5000 cm^?1 are analyzed. The assignment of numerous absorption bands to vibration modes in short methylene sequences and terminal hydroxyl groups is suggested. The splitting of IR absorption bands into doublets at 720–730 cm^?1 (rocking vibrations of CH₂ groups) and 1463–1473 cm^?1 (bending vibrations of CH₂ groups) testifies that the crystal unit subcells in the lamellae of alkanediols are orthorhombic with parameters typical of normal hydrocarbons. The specific features of absorption bands due to O-H stretching and C-O-H bending vibrations have been analyzed. These bands appear during formation of lengthy associates from hydrogen bonds formed by hydroxyl groups on the surface of elementary lamellae. A sharp increase in the intensity of the absorption bands in progression of C-C stretching and CH₂ wagging vibrations due to the anharmonic Fermi resonance with the stretching vibrations of C-O groups in the terminal hydroxyl groups has been detected.     

Vibrational analysis of substituted nitrobenzenes. I—Vibrational spectra,normal coordinate analysis and transferability of force constants of some chlorinated nitrobenzenes

The Raman and Fourier transform infrared spectra of 2,3-dichloro-, 2,4-dichloro-, 2,5-dichloro-, 3,4-dichloro-, 3,5-dichloro-, 2,3,4-trichloro-, 2,4,5-trichloro-, 2,4,6-trichloro-, 2,3,5,6-tetrachloro- and pentachloronitrobenzene were recorded. Raman polarization measurements were made wherever possible. A normal coordinate analysis was carried out for both the in-plane and out-of-plane vibrations of these molecules using a 59-parameter modified valence force field. The force constants were refined using an Overlay least-squares technique employing 352 frequencies of 10 molecules. The reliability of the force constants so obtained was tested by making a zero-order calculation for p-, m- and o-dinitrobenzenes, 1-fluoro-, 1-chloro- and 1-bromo-, 2,4-dinitrobenzenes, 2,4-difluoro- and 2,5-difluoro- and 2,5-dibromonitrobenzenes. Unambiguous vibrational assignments of all the fundamentals were made using the potential energy distribution and eigen vectors.     

The vibrational spectra of germane and silane derivatives—XI. Vibrational spectra and normal co-ordinate analyses of some thiogermanes

The i.r. and Raman spectra of the thiogermanes, (CH₃)_nH_3-n, GeSCH₃(n = 0–3) are reported and the fundamentals assigned. A normal co-ordinate analysis based on a modified valence force field supports the a priori assignments for all of the fundamental frequencies except the torsional modes.