Matrix isolation and IR spectroscopic characterization of 3,5‐difluoropyridyl‐2,4,6‐trinitrene

The photochemistry of 2,4,6‐triazido‐3,5‐difluoropyridine 21 was investigated by matrix infrared and electron paramagnetic resonance spectroscopies. Ultraviolet irradiation (>260 nm) of 21 results in the formation of 3,5‐difluoropyridyl‐2,4,6‐trinitrene 26 in yields high enough for characterization by infrared spectroscopy. The experimental infrared spectrum is in good agreement with density functional theory calculations. Under similar conditions, a very strong electron paramagnetic resonance spectrum of septet trinitrene 26 was obtained. Shorter irradiation times resulted in more complex product mixtures containing, in addition, mononitrenes and dinitrenes. Surprisingly, azirines and keteneimines, the typical photoproducts of arylnitrenes, were not observed. Copyright © 2011 John Wiley & Sons, Ltd.     

FT‐IR and FT‐Raman investigations of the chemosensing material para‐hexafluoroisopropanol aniline

As an important chemosensing material involving hexafluoroisopropanol (HFIP) for detecting nerve agents, para‐HFIP aniline (p‐HFIPA) has been firstly synthesized through a new reaction approach and then characterized by nuclear magnetic resonance and mass spectrometry experiments. Fourier transform infrared absorption spectroscopy (FT‐IR) and FT‐Raman spectra of p‐HFIPA have been obtained in the regions of 4000–500 and 4000–200 cm⁻¹, respectively. Detailed identifications of its fundamental vibrational bands have been given for the first time. Moreover, p‐HFIPA has been optimized and vibrational wavenumber analysis can be subsequently performed via density functional theory (DFT) approach in order to assist these identifications in the experimental FT‐IR and FT‐Raman spectra. The present experimental FT‐IR and FT‐Raman spectra of p‐HFIPA are in good agreement with theoretical FT‐IR and FT‐Raman spectra. Copyright © 2009 John Wiley & Sons, Ltd.     

Raman spectroscopy of hydrogen‐arsenate group (AsO3OH) in solid‐state compounds: cobalt mineral phase burgessite Co2(H2O)4[AsO3OH]2·H2O

Raman spectrum of burgessite, Co₂(H₂O)₄[AsO₃OH]₂· H₂O, was studied, interpreted and compared with its infrared spectrum. The stretching and bending vibrations of (AsO₃) and As‐OH units, as well as the stretching, bending and libration modes of water molecules and hydroxyl ions were assigned. The range of O H···O hydrogen bond lengths was inferred from the Raman and infrared spectra of burgessite. The presence of (AsO₃OH)²⁻ units in the crystal structure of burgessite was proved, which is in agreement with its recently solved crystal structure. Raman and infrared spectra of erythrite inferred from the RRUFF database are used for comparison. Copyright © 2010 John Wiley & Sons, Ltd.     

Self‐association in {2‐[3,4‐alkylenedioxy‐5‐(3‐pyridyl)]‐thienyl}alkanols: an NMR,IR, and single‐crystal X‐ray study

syn‐2,2,4,4‐Tetramethyl‐3‐{2‐[3,4‐alkylenedioxy‐5‐(3‐pyridyl)]thienyl}pentan‐3‐ols self‐associate both in the solid state and in solution. Single‐crystal X‐ray diffraction study of the 3,4‐ethylenedioxythiophene (EDOT) derivative shows that it exists as a centrosymmetric head‐to‐tail, syn dimer in the solid state. The IR spectra of the solids display only a broad OH absorption around 3300 cm^?1, corresponding to a hydrogen‐bonded species. ¹H Nuclear Overhauser Effect Spectroscopy (NOESY) NMR experiments in benzene reveal interactions between the tert‐butyl groups and the H2 and H6 protons of the pyridyl group. Two approaches have been used to determine association constants of the EDOT derivative by NMR titration, based on the concentration dependence of (i) the syn/anti ratio and (ii) the OH proton shift of the syn rotamer. Reasonably concordant results are obtained from 298 to 323 K (3.6 and 3.9 M^?1, respectively, at 298 K). Similar values are obtained from the syn OH proton shift variation for the 3,4‐methylenedioxythiophene (MDOT) derivative. Concentration‐dependent variation of the anti OH proton shift in the latter suggests that the anti isomer associates in the form of an open, singly hydrogen‐bonded dimer, with a much smaller association constant than the syn rotamer. Self‐association constants for 3‐pyridyl‐EDOT‐alkanols with smaller substituents vary by a factor of 4 from (i‐Pr)₂ up to (CD₃)₂, while the hetero‐association constants for the same compounds with pyridine vary slightly less. Copyright © 2007 John Wiley & Sons, Ltd.     

Spectroscopic and structural investigations of α‐, β‐, and γ‐AlH3 phases

With its reputation as a high‐energy density fuel, aluminum hydride (AlH₃) has received renewed attention as a material that is particularly suitable, not only for hydrogen storage but also for rocket propulsion. While the various phases of AlH₃ have been investigated theoretically, there is a shortage of experimental studies corroborating the theoretical findings. In response to this, we present here an investigation of these compounds based primarily on two research areas in which there is the greatest scarcity of information in the literature, namely Raman and infrared (IR) absorption analysis. To the authors' knowledge, this is the first report of experimental far‐IR absorption results on these compounds. Two different samples prepared by broadly similar ethereal reactions of AlCl₃ with LiAlH₄ were analyzed. Both Raman and IR absorption measurements indicate that one sample is purely γ‐AlH₃ and that the other is a mixture of α‐, β‐, and γ‐AlH₃ phases. X‐ray diffraction confirms the spectroscopic findings, most notably for the β‐AlH₃ phase, for which optical spectroscopic data are reported here for the first time. Copyright © 2010 John Wiley & Sons, Ltd.     

Acid assisted proton transfer in 4‐[(4‐R‐phenylimino)methyl]pyridin‐3‐ols: NMR spectroscopy in solution and solid state,X‐ray and UV studies and DFT calculations

The behaviour of Schiff bases of 3‐hydroxy‐4‐pyridincarboxaldehyde and 4‐R‐anilines (R?H, CH₃, OCH₃, Br, Cl, NO₂) in acid media has been described. ¹H, ¹³C, ¹⁵N‐NMR chemical shifts allow to establish the protonation site and its influence on the hydroxyimino/oxoenamino tautomerism. DFT calculations, electronic spectra and X‐ray diffraction are in agreement with the NMR conclusions. Copyright © 2007 John Wiley & Sons, Ltd.     

Intra‐ versus intermolecular hydrogen bonding equilibrium in 2‐hydroxy‐N,N‐diethylbenzamide

Complex studies of the intramolecular versus intermolecular hydrogen bond equilibrium and internal rotation of the N,N‐diethylamine group in 2‐hydroxy‐N,N‐diethylbenzamide were conducted. The intramolecular versus intermolecular process in 2‐hydroxy‐N,N‐diethylbenzamide was studied by UV–Vis, NMR, IR and Vapour Pressure Osmometric (VPO) methods as a function of temperature and concentration in non‐polar, basic and protic solvents. The unequal positions of the ethyl groups were analysed and the energy barrier to the re‐orientation was defined by the NMR method. This paper presents a study into a complicated nature of competitive interaction 2‐hydroxy‐N,N‐diethylbenzamide with the environment by means of the aforesaid methods. Copyright © 2008 John Wiley & Sons, Ltd.     

Distinguishing chemical and electromagnetic enhancement in surface‐enhanced Raman spectra: The case of para‐nitrothiophenol

Surface‐enhanced Raman spectra are simulated using a combined classical electrodynamics/real‐time time‐dependent density functional theory approach and compared to experiments. Emphasis is put on discerning between chemical and electromagnetic enhancement. Therefore, three different calculation scenarios are investigated using para‐nitrothiophenol as a test molecule. In the first one, corresponding to electromagnetic enhancement, we simulate the molecule alone with ab initio computations incorporating the electromagnetic field emitted by a nanoparticle. Chemical enhancement is modeled in the second scenario, where we include not only the molecule into the quantum chemistry calculations but also metal atoms of the nanoparticle. Here, any modification of the electromagnetic field due to the nanoparticle is not considered. In the third scenario, the former two setups are combined and demanding simulations of the hybrid system containing the molecule and the metal atoms exposed to a strongly modified electromagnetic field due to the plasmonic properties of the metallic nanoparticles are considered. Results are compared to our experimentally measured spectra. Based on our analysis, we show here on rigorous grounds that the electromagnetic effect leads to increased absolute Raman scattering cross sections but no change of the relative intensities. In contrast, the chemical effect leads to changes in relative peak height and also to newly emerging bands in the spectrum. These findings will have major implications in any study that concerns the interaction of molecules with metallic nanostructures. Copyright © 2013 John Wiley & Sons, Ltd.     

Catalysis by hydrogen chloride in the gas‐phase elimination kinetics of 2‐phenyl‐2‐propanol and 3‐methyl‐1‐buten‐3‐ol

A homogeneous, molecular, gas‐phase elimination kinetics of 2‐phenyl‐2‐propanol and 3‐methyl‐1‐ buten‐3‐ol catalyzed by hydrogen chloride in the temperature range 325–386 °C and pressure range 34–149 torr are described. The rate coefficients are given by the following Arrhenius equations: for 2‐phenyl‐2‐propanol log k₁ (s^?1) = (11.01 ± 0.31) ? (109.5 ± 2.8) kJ mol^?1 (2.303 RT)^?1 and for 3‐methyl‐1‐buten‐3‐ol log k₁ (s^?1) = (11.50 ± 0.18) ? (116.5 ± 1.4) kJ mol^?1 (2.303 RT)^?1. Electron delocalization of the CH₂?CH and C₆H₅ appears to be an important effect in the rate enhancement of acid catalyzed tertiary alcohols in the gas phase. A concerted six‐member cyclic transition state type of mechanism appears to be, as described before, a rational interpretation for the dehydration process of these substrates. Copyright © 2007 John Wiley & Sons, Ltd.     

Trends in properties of para‐substituted 3‐(phenylhydrazo)pentane‐2,4‐diones

Trends between the Hammett's σ_p and related normal , inductive σ_I, resonance σ_R, negative and positive polar conjugation and Taft's σ_p° substituent constants and the distance, δ_{N? H} NMR chemical shift, oxidation potential (E_p/2°x, measured in this study by cyclic voltammetry (CV)) and thermodynamic parameters (pK, ΔG⁰, ΔH⁰ and ΔS⁰) of the dissociation process of unsubstituted 3‐(phenylhydrazo)pentane‐2,4‐dione (HL₁) and its para‐substituted chloro (HL₂), carboxy (HL₃), fluoro (HL₄) and nitro (HL₅) derivatives were recognized. The best fits were found for σ_p and/or in the cases of , δ_{N? H} and E_p/2°x, showing the importance of resonance and conjugation effects in such properties, whereas for the above thermodynamic properties the inductive effects (σ_I) are dominant. HL₂ exists in the hydrazo form in DMSO solution and in the solid state and contains an intramolecular H‐bond with the distance of 2.588(3) Å. It was also established that the dissociation process of HL_1–5 is non‐spontaneous, endothermic and entropically unfavourable, and that the increase in the inductive effect (σ_I) of para‐substitutents (? H < ? Cl < ? COOH < ? F < ? NO₂) leads to the corresponding growth of the distance and decrease of the pK and of the changes of Gibbs free energy, of enthalpy and of entropy for the HL_1–5 acid dissociation process. The electrochemical behaviour of HL_1–5 was interpreted using theoretical calculations at the DFT/HF hybrid level, namely in terms of HOMO and LUMO compositions, and of reactivities induced by anodic and cathodic electron‐transfers. Copyright © 2010 John Wiley & Sons, Ltd.     

Computational studies of the effects of ortho‐ring and para‐ring activation on the kinetics of SNAr reactions of 1‐chloro‐2‐nitrobenzene and 1‐phenoxy‐2‐nitrobenzene with aniline

Computational studies are reported for reactions of 4‐substituted‐1‐chloro‐2,6‐dinitrobenzenes 1 , 6‐substituted‐1‐chloro‐2,4‐dinitrobenzenes 2 and some of the corresponding 1‐phenoxy derivatives 3 and 4 with aniline in the gas phase. The effects of substituent groups in the calculated energy values for reactants 1–4 , transition states structures, intermediates and products formed in the reactions between the compounds and anilines have been compared. Calculated bonds length and angles from optimized structures of the reactants were comparable with values reported for some of compounds 1–4 obtained by X‐ray crystal structures analysis. Generally, the decomposition of the Meisenheimer intermediate to the products requires more energy compared with the reactants except for when R = H. The order of stabilization of the intermediate was found to reflect the relative order of activation by substituents in the substrates. The 4‐substituted‐1‐chloro‐2,6‐dinitrobenzenes 1 and the phenoxy derivatives 3 were found to be more stable than their corresponding 6‐substituted analogues. This is an indication that the rate of nucleophilic attack at 1‐position will increase with increasing ring activation but may be reduced by steric repulsion at the reaction centre that increases in the order Cl < OPh. However, the steric hindrance to the steps involved in nucleophilic substitution by aniline is significantly increased when the substrates contain two ortho‐substituents. In most cases, the rate determining step is the decomposition of the σ‐adduct intermediate except with 1‐chloro‐2,6‐dinitrobenzenes 1 and 6‐substituted‐1‐chloro‐2,4‐dinitrobenzenes 2 , either because of reduction in ring activation or the presence of bulky ortho‐substituents in the chloro compounds 1 and 2 . Copyright © 2014 John Wiley & Sons, Ltd.     

The equilibrium and kinetics of intermolecular hydrogen bonding in nitroarene anion radical–alcohol system: 1,3‐dinitro‐benzene anion radical – R–OH (R═CH3–, C2H5–, (CH3)2 CH–)

To explore the possibility of hydrogen bonding of a stable anion radical with DNA – component sugar, hormones, steroid, and so on (through hydroxyl group), as a first step, the possibility of hydrogen bonding of 1,3‐dinitrobenzene anion radical (1,3‐DNB^??) with aliphatic alcohols was studied. It was found that 1,3‐DNB^?? anion radical undergoes hydrogen bonding with alcohols: methanol, ethanol, and 2‐proponal. The hydrogen‐bonding equilibrium constant K_eq and the (hydrogen‐bonding) rate constants k₂ were evaluated through the use of linear scan and cyclic voltammetry theory and techniques. The K_eq was found to be in the range of 1.4–6.0 m ^?1, whereas the rate constants k₂ were found to be in the range of 1.5–3.6 m ^?1 s^?1, depending upon the hydrogen‐bonding agent and the equation used for the calculation of the rate constants. The hydrogen‐bonding number n was found to be around 0.5 or 1.0. The implication of this study in, for example, the replication of DNA, the prevention of the formation of super oxide, and so on is discussed. Copyright © 2012 John Wiley & Sons, Ltd.     

A three‐crystal spectrometer for high‐energy resolution fluorescence‐detected X‐ray absorption spectroscopy and X‐ray emission spectroscopy at SSRF

A Johann‐type spectrometer for the study of high‐energy resolution fluorescence‐detected X‐ray absorption spectroscopy, X‐ray emission spectroscopy and resonant inelastic X‐ray scattering has been developed at BL14W1 X‐ray absorption fine structure spectroscopy beamline of Shanghai Synchrotron Radiation Facility. The spectrometer consists of three crystal analyzers mounted on a vertical motion stage. The instrument is scanned vertically and covers the Bragg angle range of 71.5–88°. The energy resolution of the spectrometer ranges from sub‐eV to a few eV. The spectrometer has a solid angle of about 1.87 × 0^?3 of 4π sr, and the overall photons acquired by the detector could be 10⁵ counts per second for the standard sample. The performances of the spectrometer are illustrated by the three experiments that are difficult to perform with the conventional absorption or emission spectroscopy. Copyright © 2016 John Wiley & Sons, Ltd.     

Vibrational characterization of L‐valine phosphonate dipeptides: FT‐IR,FT‐RS,and SERS spectroscopy studies and DFT calculations

Four L ‐valine (L ‐Val) phosphonate dipeptides that are potent inhibitors of zinc metalloproteases, namely, L ‐Val‐C(Me)₂‐PO₃H₂ (V1), L ‐Val‐CH(iP)‐PO₃H₂ (V2), L ‐Val‐CH(iB)‐PO₃H₂ (V3), and L ‐Val‐C(Me)(iP)‐PO₃H₂ (V4), are studied by Fourier‐transform infrared (FT‐IR) spectroscopy, Fourier‐transform Raman spectroscopy (FT‐RS), and surface‐enhanced Raman scattering (SERS). The band assignment (wavenumbers and intensities) is made based on (B3LYP/6‐311 + + G**) calculations. Comparison of theoretical FT‐IR and FT‐RS spectra with those of SERS allows to obtain information on the orientation of these dipeptides as well as specific‐competitive interactions of their functionalities with the silver substrate. More specifically, V1 and V4 appear to interact with the silver substrate mainly via a  C_sgCH₃ moiety localized at the  N_amideC_sg(CH₃)P molecular fragment. In addition, the  POH and isopropyl units of V4 assist in the adsorption process of this molecule. In contrast, the  C_αNH₂ and  PO₃H⁻ groups of V2 and V3 interact with the silver nanoparticles, whereas their isopropyl and isobutyl fragments seem to be repelled by the silver substrate (except for the  CH₂  of V3), similar to the  C_β(CH₃)₂ fragment of L ‐Val for all L ‐Val phosphonate dipeptides investigated in this work. The adsorption mechanism of these molecules onto the colloidal silver surface is also affected by amide bond behavior. Copyright © 2010 John Wiley & Sons, Ltd.     

Vibrational spectroscopy and DFT calculations of di‐amino acid peptides: α‐ and β‐N‐acetyl‐L‐Asp‐L‐Glu in the solid state

Experimental vibrational spectroscopic studies and density functional theory (DFT) calculations of the di‐amino acid peptide derivatives α‐ and β‐N‐acetyl‐L‐Asp‐L‐Glu have been undertaken. Raman and infrared spectra have been recorded for samples in the solid state. DFT simulations were conducted using the B3‐LYP correlation functional and the cc‐pVDZ basis set to determine energy minimized/geometry optimized structures (based on a single isolated molecule in the gaseous state). Normal coordinate calculations have provided vibrational assignments for fundamental modes, including their potential energy distributions. Significant differences are observed between α‐ and β‐N‐acetyl‐L‐Asp‐L‐Glu both in the computed structures and in the vibrational spectra. The combination of experimental and calculated spectra provide an insight into the structural and vibrational spectroscopic properties of di‐amino acid peptide derivatives. Copyright © 2009 John Wiley & Sons, Ltd.     

Neon matrix isolation spectroscopy of CO2 isotopologues

The solid neon matrix isolated spectrum of CO₂ are recorded in the 2–5 μm region. Natural and ¹³C or ¹⁸O enriched CO₂ samples were used and the nν₁ + ν₃ (n = 0, 1, 2) series bands of different CO₂ isotopologues have been observed. The solid neon matrix shift due to Fermi-resonance of bands within the same vibrational polyad is analyzed.     

The electronic delocalization in para‐substituted β‐nitrostyrenes probed by resonance Raman spectroscopy and quantum‐chemical calculations

The electronic (UV‐vis) and resonance Raman (RR) spectra of a series of para‐substituted trans‐β‐nitrostyrenes were investigated to determine the influence of the electron donating properties of the substituent (X = H, NO₂, COOH, Cl, OCH₃, OH, N(CH₃)₂, and O⁻) on the extent of the charge transfer to the electron‐withdrawing NO₂ group directly linked to the ethylenic (C = C) unit. The Raman spectra and quantum chemical calculations show clearly the correlation of the electron donating power of the X group with the wavenumbers of the ν_s(NO₂) and ν (C = C)_sty normal modes. In conditions of resonance with the lowest excited electronic state, one observes for X = OH and N(CH₃)₂ that the symmetric stretching of the NO₂, ν_s(NO₂), is the most substantially enhanced mode, whereas for X = O⁻, the chromophore is extended over the whole molecule, with substantial enhancement of several carbon backbone modes. Copyright © 2008 John Wiley & Sons, Ltd.     

Organic cyclic difluoramino‐nitramines: infrared and Raman spectroscopy of 3,3,7,7‐tetrakis(difluoramino)octahydro 1,5‐dinitro‐1,5‐diazocine (HNFX)

We present the first vibrational structure investigation of 3,3,7,7‐tetrakis(difluoramino)octahydro‐1,5‐dinitro‐ 1,5‐diazocine (HNFX)—and, more generally, of a member of the new class of gem‐bis(difluoramino)‐substituted heterocyclic nitramine energetic materials—using combined theoretical and experimental approaches. Optimized molecular structure and vibrational spectra of the Ci… symmetry conformer constituting the HNFX crystal were computed using density functional theory methods. Fourier transform infrared and Raman spectra of HNFX crystalline samples were also collected at ambient temperature and pressure. The average deviation of calculated structural parameters from X‐ray diffraction data is ∼1% at the B3LYP/6‐311 + + G(d,p) level of theory, suggesting the absence of significant molecular distortion induced by the crystal field. Very good agreement was found between simulated and measured spectra, allowing reliable assignment of the fundamental normal modes of vibration of the HNFX crystal. Detailed analysis of the normal modes of the C–(NF₂)₂ and N–NO₂ moieties was performed due to their critical importance in the initial steps of the molecular homolytic fragmentation process. Copyright © 2009 John Wiley & Sons, Ltd.     

Conformational analysis of 3‐methyl‐3‐silathiane and 3‐fluoro‐3‐methyl‐3‐silathiane

The conformational equilibria of 3‐methyl‐3‐silathiane 5 , 3‐fluoro‐3‐methyl‐3‐silathiane 6 and 1‐fluoro‐1‐methyl‐1‐silacyclohexane 7 have been studied using low temperature ¹³C NMR spectroscopy and theoretical calculations. The conformer ratio at 103 K was measured to be about 5 _ax: 5 _eq = 15:85, 6 _ax: 6 _eq = 50:50 and 7 _ax: 7 _eq = 25:75. The equatorial preference of the methyl group in 5 (0.35 kcal mol^?1) is much less than in 3‐methylthiane 9 (1.40 kcal mol^?1) but somewhat greater than in 1‐methyl‐1‐silacyclohexane 1 (0.23 kcal mol^?1). Compounds 5–7 have low barriers to ring inversion: 5.65 (ax → eq) and 6.0 (eq → ax) kcal mol^?1 ( 5 ), 4.6 ( 6 ), 5.1 (Me_ax → Me_eq) and 5.4 (Me_eq → Me_ax) kcal mol^?1 ( 7 ). Steric effects cannot explain the observed conformational preferences, like equal population of the two conformers of 6 , or different conformer ratio for 5 and 7 . Actually, by employing the NBO analysis, in particular, considering the second order perturbation energies, vicinal stereoelectronic interactions between the Si–X and adjacent C–H, C–S, and C–C bonds proved responsible. Copyright © 2010 John Wiley & Sons, Ltd.     

FT‐IR,FT‐Raman and DFT calculations of the salicylanilide derivate 4‐chloro‐2‐(4‐bromophenylcarbamoyl)phenyl acetate

FT‐IR and FT‐Raman spectra of 4‐chloro‐2‐(4‐bromophenylcarbamoyl)phenyl acetate were recorded and analyzed. The vibrational wavenumbers and corresponding vibrational assignments were examined theoretically using the Gaussian03 set of quantum chemistry codes. The red shift of the NH stretching wavenumber in the infrared (IR) spectrum from the computed wavenumber indicates the weakening of the NH bond resulting in proton transfer to the neighbouring oxygen atom. The simultaneous IR and Raman activations of the CO stretching mode give the charge transfer interaction through a π‐conjugated path. Optimized geometrical parameters of the title compound are in agreement with similar reported structures. From the optimized structure, it is clear that the hydrogen bonding decreases the double bond character of CO bond and increases the double bond character of the C N bonds. The first hyperpolarizability, predicted infrared intensities and Raman activities are reported. The calculated first hyperpolarizability is comparable with the reported values of similar derivatives and is an attractive object for future studies of non‐linear optics. The assignments of the normal modes are done by potential energy distribution (PED) calculations. Copyright © 2009 John Wiley & Sons, Ltd.