A selective and cost-effective method for the reductive deuteration of activated alkenes

A new single electron transfer reaction for the reductive deuteration of activated alkenes has been developed for the selective synthesis of α,β-dideuterio compounds. A cheap, stable and commercially-available sodium dispersion with high specific surface area is employed as the electron donor to replace the traditionally used sodium/liquid ammonium system. Deuterium source is provided by EtOD-d₁. Excellent yields and deuterium incorporations were obtained across a broad range of activated alkenes with good functional group tolerance. This method provided a cheap, efficient and operationally-simple method for the synthesis of deuterium labeled compounds.     

Infrared and Raman study of thiobisamines

The i.r. and Raman spectra of various N,N′-thiobisamines were investigated. By comparing the spectra with those of the corresponding amines, an assignation of bands characteristic of NSz.sbnd;N structures is proposed. From the estimation of the force constants of the SN bonds followed by their correlation with the interatomic distances, the SN bond orders were evaluated. These bond orders, which depend only slightly on the nature of the amine, indicate some double bond character for the SN linkage.     

A study of the internal dynamics of trimethylamine by means of the non-rigid group theory

The non-rigid molecule group theory (NRG) in which the dynamical symmetry operations are defined as physical operations is applied to determine the character table for the triple equivalent methyl rotation and pyramidal inversion in trimethylamine. The restricted NRG of this molecule is seen to be a group of order 648, formed as a product of two subgroups: the G ₃₂₄ subgroup corresponding to planar trimethylamine and the pyramidal inversion. For this purpose the structure of the r-NRG of planar trimethylamine is first deduced, i.e., the number of classes, irreducible representations, as well as their dimensions. Finally, guidelines are given to deduce systematically the symmetry eigenvectors developed on the basis of quadruple products of trigronometric functions. The r-NRG molecule group theory is seen to be used advantageously to study the internal dynamics of such small organic molecules.     

A simple, efficient, and selective deuteration via a flow chemistry approach

A simple and efficient deuteration methodology has been established for a wide variety of substrates using a continuous flow hydrogenation reactor. The described procedure is many times faster (1 mg min⁻¹) compared to literature methods and the purity of the crude product can be as high as 99%. The deuterium source is D₂O, the consumption of which is very low.     

Slow motion of long-chain molecules in solution with internal correlations

The Rouse equations for the dissipative motion of long-chain molecules are reformulated in terms of coupled Langevin equations. While in the conventional Rouse model the random forces acting on each bead are supposed to be uncorrelated, the calculation given here admits of any correlation between the forces. By virtue of the second fluctuation dissipation theorem this corresponds to an added friction factor, called the “internal viscosity” in agreement with earlier work of Kuhn and Kuhn, Cerf, and of Peterlin. In the mode decomposition, this added friction factor happens to be an even function of the mode frequency. From this general model it is possible to compute formally the mean-square displacement function. It takes a simple form if one assumes that forces are correlated only on adjacent beads and that their correlation functions are δ functions. The results of the calculation are best displayed in the Fourier transform of the meansquare displacement, which is directly related to the neutron incoherent scattering cross section. It is seen that the presence of internal viscosity modifies the behavior of the chain for a time scale of the order of the relaxation time of the elementary segment.     

A simple, cost-effective method for the regioselective deuteration of anilines

A highly effective and operationally simple method for the regioselective deuteration of anilines is presented. A variety of electron-rich and electron-deficient anilines are efficiently deuterated at the ortho and/or para position with respect to the nitrogen in the presence of 1 equiv of conc HCl in D 2O. Under the present conditions, aromatic methoxy groups do not facilitate deuteration, enabling a chemo- and regioselective deuteration of p-anisidine.     

Raman study of reorientational motion of liquid benzene

Raman spectra of the 943 cm^?1 band of liquid benzene-d₆ were measured at temperatures up to 120°C and at pressures up to 4000 bar. Rotational diffusion constants for tumbling and spinning motions were obtained from Raman band widths and NMR T₁ data. Experimental results were compared with theoretical diffusion constants computed on the basis of various models. It is found that the Hynes—Kapral—Weinberg theory gives the best prediction for the temperature and pressure dependence of the diffusion constants and for the rotational anisotropy in liquid benzene.     

Raman linewidth study of molecular motion in triethylenediamine

Reorientational relaxation of plastic crystalline triethylenediamine and vibrational relaxation of triethylenediamine in solution, using Raman line-shape analysis have been studied. The results are compared with the predictions of Kubo stochastic theory and with results obtained by other techniques.     

Re-evaluation of the model-free analysis of fast internal motion in proteins using NMR relaxation

NMR spin relaxation retains a central role in the characterization of the fast internal motion of proteins and their complexes. Knowledge of the distribution and amplitude of the motion of amino acid side chains is critical for the interpretation of the dynamical proxy for the residual conformational entropy of proteins, which can potentially significantly contribute to the entropy of protein function. A popular treatment of NMR relaxation phenomena in macromolecules dissolved in liquids is the so-called model-free approach of Lipari and Szabo. The robustness of the mode-free approach has recently been strongly criticized and the remarkable range and structural context of the internal motion of proteins, characterized by such NMR relaxation techniques, attributed to artifacts arising from the model-free treatment, particularly with respect to the symmetry of the underlying motion. We develop an objective quantification of both spatial and temporal asymmetry of motion and re-examine the foundation of the model-free treatment. Concerns regarding the robustness of the model-free approach to asymmetric motion appear to be generally unwarranted. The generalized order parameter is robustly recovered. The sensitivity of the model-free treatment to asymmetric motion is restricted to the effective correlation time, which is by definition a normalized quantity and not a true time constant and therefore of much less interest in this context. With renewed confidence in the model-free approach, we then examine the microscopic distribution of side chain motion in the complex between calcium-saturated calmodulin and the calmodulin-binding domain of the endothelial nitric oxide synthase. Deuterium relaxation is used to characterize the motion of methyl groups in the complex. A remarkable range of Lipari-Szabo model-free generalized order parameters are seen with little correlation with basic structural parameters such as the depth of burial. These results are contrasted with the homologous complex with the neuronal nitric oxide synthase calmodulin-binding domain, which has distinctly different thermodynamic origins for high affinity binding.     

Raman,spectra of matrix-isolated lead molecules

Raman spectra of lead molecules in low-temperature rare-gas matrices show that dimers and larger clusters are isolated. Besides 7 “normal” Raman bands, two strong resonance progressions are found with frequencies of 108.5 and 118.5 cm^?1 in Xe and 111 and 119 cm^?1 in Kr. The 110 cm^?1 peak is assigned to Pb₂, close to the frequency for the X-O⁺_g state of gaseous Pb₂.     

Infrared and Raman spectroscopic study of 1,2-benzenedithiol adsorbed on silver

Adsorption of 1,2-benzenedithiol (1,2-BDT) on a silver surface has been investigated by surface-enhanced Raman (SER) and reflection-absorption infrared (RAI) spectroscopy. The molecule was adsorbed on silver very favorably by forming two Ag---S bonds after deprotonation. From the RAI spectral pattern, the benzene ring of adsorbed 1,2-BDT was presumed to be tilted by ca. 38° from the surface normal. This RAI information was used to test the validity of various proposed SER selection rules. Being frequently quoted in the literature, the presence or absence of the benzene ring CH stretching vibration in the SER spectrum seemed, in fact, to be a very useful indicator in judging the perpendicular or parallel orientation of the benzene ring with respect to the surface. However, the so-called in-plane/out-of-plane dichotomy as well as the more elaborate symmetry-based electromagnetic selection rule was found not to work in the present system.     

Infrared and Raman spectra, conformational stability, barriers to internal rotation, normal-coordinate calculations and vibrational assignments for vinyl silyl bromide

The infrared (3200-30 cm(-1) spectra of gaseous and solid, the Raman spectra (3200-30 cm(-1)) of the liquid and solid vinyl silyl bromide, CH2CHSiH2Br, have been recorded. Additionally, quantitative depolarization values have been obtained. Both the gauche and cis conformers have been identified in the fluid phases but only the gauche conformer remains in the solid. Variable temperature studies from 0 to -87 degrees C of the Raman spectrum of the liquid was carried out. From these data, the enthalpy difference has been determined to be 22 +/- 6 cm(-1) (0.26 +/- 0.08 kJ/mol), with the gauche conformer being the more stable form. The predictions from the ab initio calculations up to MP2/6-311 + + G(2d,2p) basis set favor the gauche as the more stable form. A complete vibrational assignment is proposed for both the gauche and cis conformers based on infrared band contours, relative intensities, depolarization values and group frequencies. The vibrational assignments are supported by normal coordinate calculations utilizing the force constants from ab initio MP2/6-31G(d) calculations and the potential energy terms for the conformer interconversion have been obtained from the same calculations. Complete equilibrium geometries have been determined for both rotamers by ab initio calculations employing a variety of basis sets up to 6-311 + + G(2d,2p) at levels of restricted Hartree-Fock (RHF) and/or Moller-Plesset (MP) to second order. The results are discussed and compared to those obtained for some similar molecules.     

Infrared and Raman spectra,conformational stability,barriers to internal rotation,ab initio calculations and vibrational assignment of ethyl methyl selenide

The Raman spectra (3200–10 cm⁻¹) of ethyl methyl selenide in the gas, liquid and solid phases and the infrared spectra (3200–30 cm⁻¹) of the gas and solid have been recorded. Qualitative depolarization ratios have been obtained for the lines in the Raman spectrum of the liquid. By a variable temperature Raman study of the liquid, it has been determined that the gauche conformer is more stable than the trans rotamer by 158±16 cm⁻¹ (452±46 cal mol⁻¹), and the gauche conformer is the rotamer present in the solid. A complete vibrational assignment for the gauche conformer is presented. All of these data are compared to the corresponding quantities obtained from ab initio Hartree—Fock gradient calculations employing the STO-3G* and 4–31G*/MIDI-4* basis sets. Complete equilibrium geometries have been calculated for both rotamers and the results are discussed and compared with the corresponding quantities for some similar molecules.     

Infrared and Raman spectra of N-n-alkylthioureas

The i.r. and Raman spectra of solid alkyl thioureas H₂NCSNH(CH₂)nCH₃ (n = 0–15), TUR′, and their urea analogue H₂NCONH(CH₂)nCH₃ (n = 0–9), UR′, are presented. The vibrational properties of N-monosubstituted TUR′and UR′are studied on the basis of the spectral comparison between the members of the series and compared with the properties of N,N′-di-substituted MTUR′ and MUR′, correspondingly. Some features of the methylene ν₄ and ν₇ band progressions were found to shift from the corresponding features of solid n-alkanes by vibrational coupling. The observed wavenumber of the longitudinal accordion-like skeletal motion (LAM-1) of TUR′ was found to correspond to that of the n-alkane with the same number of carbon atoms as TUR′ has skeletal atoms.     

Infrared and Raman spectra of phtalic,isophtalic and terephtalic acids

The i.r. spectra of phtalic, isophtalic and terephtalic acids as KBr pellets as well as Raman spectra of microcrystalline powder have been investigated. Most vibrations have been assigned by correlation with the spectra of the previously studied phtalate, isophtalate and terephtalate ions. The COOH characteristic vibrations have been assigned as vibrations of the hydrogen-bonded centrosymmetric “dimers” COOH … HOOC, and a general assignment is proposed for combination bands in the range 3000-2500 cm⁻¹.     

Infrared and Raman spectra of phtalate,isophtalate and terephtalate ions

Infrared spectra of anhydrous dipotassic salts of phtalic, isophtalic and terephtalic acids in KBr pellets as well as their Raman spectra as microcrystalline powder and saturated aqueous solutions, have been investigated. On this basis, a tentative assignment of the observed vibrational bands is proposed for each ion, the relevant molecular point groups being C₂, C_2ν and D_2h respectively. Characteristic COO⁻ vibrations show frequencies which do not change noticeably from one to other ion, with the exception of γ(OCO) which appears in the spectrum of terephtalate ion some 150 cm⁻¹ higher than in the other two cases.     

Protonation,deuteration, and formylation of aceperidazylenes

1H-1,2-Diazaphenalene derivatives in which the pyridazine ring is ortho- and peri-fused to acenaphthene and acenaphthylene (1H-indeno[6,7,1-def]cinnolines) have been synthesized. It has been found that electrophilic attack on these compounds is directed at C⁶.     

Infrared and Raman imaging of heterogeneous catalysts

The miniaturization of in situ spectroscopic tools has been recognized as a forefront instrumental development for the characterization of heterogeneous catalysts. With the multitude of micro-spectroscopic methods available fundamental insight into the structure-function relationships of catalytic processes can be obtained. Among these techniques vibrational spectroscopy is one of the most versatile methods and capable to shed insight into the molecular structure of reaction intermediates and products, the chemical state of catalyst materials during reaction as well as the nature of interactions between reactants/intermediates/products and the catalyst surface. In this tutorial review we discuss the recent developments in the field of infrared (IR) and Raman micro-spectroscopy and illustrate their potential. Showcase examples include (1) chemical imaging of spatial heterogeneities during catalyst preparation, (2) high-throughput catalyst screening, (3) transport and adsorption phenomena within catalytic solids and (4) reactivity studies of porous oxides, such as zeolites. Finally, new in situ spectroscopy tools based on vibrational spectroscopy and their potential in the catalysis domain are discussed.     

Infrared and Raman spectra of pyromellitic dithioanhydride

The i.r. spectrum of pyromellitic dithioanhydride has been measured from 4000 to 200 cm⁻¹; polarized i.r. spectra of single crystals have been also obtained. The Raman spectra of polycrystalline samples and solutions have been recorded and polarization of many lines has been determined. A detailed assignment of most of the fundamentals has been proposed on the basis of i.r. dichroism of the single crystals, Raman spectra and analogies with the spectra of related molecules.