Normal co-ordinate analysis of 1, 8-dibromooctane

The organic compound 1,8-dibromooctane (1,8-DBO) exists in liquid phase at ambient temperatures and has versatile synthetic applications. In its liquid phase 1,8-DBO has been expected to exist in four most probable conformations, with all its carbon atoms in the same plane, having symmetries C _2h , C _i , C ₂ and C ₁ . In the present study a detailed vibrational analysis in terms of assignment of Fourier transform infrared (FT-IR) and Raman bands of this molecule using normal co-ordinate calculations has been done. A systematic set of symmetry co-ordinates has been constructed for this molecule and normal co-ordinate analysis is carried out using the computer program MOLVIB. The force-field transferred from already studied lower chain bromo-alkanes is subjected to refinement so as to fit the observed infrared and Raman frequencies with those of calculated ones. The potential energy distribution (PED) has also been calculated for each mode of vibration of the molecule for the assumed conformations.     

Spectre de photoélectrons He(I) De l'hexafluorobicyclo[2,2,0]-hexadiéne-2,5

The He(I) photoelectron spectrum of C₆F₆ (hexafluorobicyclo[2.2.0]hexa-2,5-diene) has been recorded. The ionization energy of the compound is measured to be 10.08 eV. The energy difference, 0.87 eV, between the two first bands of the PE spectrum is attributed to homoconjugation (through-space interaction) between the two double bonds. The highest occupied MO is shown to be of b₂ symmetry (C_2v group), the next one being of a₁ symmetry.EXTHUC, CNDO and INDO methods have been used to calculate the changes of the total energy of the molecule and of the two highest occupied MO's upon variation of the dihedral angle of the molecule.     

Self-assembled line growth of allyl alcohol on the H-terminated Si(100)-(2 × 1) surface

Using first-principles density-functional calculations, we investigate the growth mechanism of allyl alcohol (ALA) line on the H-terminated Si(100)-(2 × 1) surface. Unlike the allyl mercaptan (CH₂ = CH ? CH₂ ? SH) line, which was observed to grow across the Si dimer rows, we find that ALA (CH₂ = CH ? CH₂ ? OH) has the line growth along the Si dimer row. The self-assembled growth of ALA line occurs via the radical chain reaction mechanism, similar to the case of a typical alkene molecule, styrene. Our calculated energy profile along the reaction pathway shows that the different growth direction of ALA line compared with that of allyl mercaptan line is ascribed to the great instability of the oxygen radical intermediate, which prevents the line growth across the dimer rows.     

Spin-spin and spin-other-orbit effects of optical spectra and the spin-Hamiltonian parameters for Cr ions in MgO crystals

An extended complete diagonalization method/microscopic spin-Hamiltonian (CDM/MSH) program has been developed, which is applicable for d³ ions at sites of tetragonal symmetry type I (C_4v, D_2d, D₄, D_4h) and trigonal symmetry type I (C_3v, D₃, D_3d). The Hamiltonian includes the spin-spin (SS) and spin-other-orbit (SOO) magnetic interactions besides the spin-orbit (SO) magnetic interaction usually taken into account. Utilizing the extended CDM/MSH program, the optical spectra, the spin-Hamiltonian (SH) parameters of the ground state ⁴B₁, and the splitting δ(²E) of the first excited ²E state for Cr³⁺ (3d³) ions at C_4v symmetry sites in MgO crystals have been successfully investigated. It is found that although the SO magnetic interaction is the most important one, the contributions to the SH parameters and the optical spectra from the SS and SOO magnetic interactions for Cr³⁺:MgO crystals are appreciable and should not be omitted, especially reaching 27.8% for the zero field splitting parameter D.     

Vibrational spectra, normal coordinate analysis and thermodynamics of 2, 5-difluorobenzonitrile

The FTIR spectrum of 2, 5-difluorobenzonitrile has been recorded in the region 200–4000 cm⁻¹ (in liquid phase). The laser Raman spectrum in the range of 0–3500 cm⁻¹ (in liquid phase) has also been recorded. The spectra have been analyzed assuming C _s point group symmetry for the molecule. A zero-order normal coordinate analysis has been made for the molecule using force constants derived earlier. On the basis of potential energy distributions and eigen vectors unambiguous vibrational assignments have been made for all the fundamentals of the molecule. Thermodynamic functions have also been computed in the temperature range 200–1000 K by utilizing the observed fundamental frequencies assuming rigid-rotor harmonic oscillator approximation.     

Some CNDO Calculations and Structural Spectroscopic Studies of Paracetamol Complexes

Through complete neglect of differential overlap (CNDO) calculations of the electronic energy among different possible structures of paracetamol (PA) molecule, it has been concluded that its structure has C_s point group symmetry of the cis‐form in which the methyl group has a restricted free rotation around its bond with the carbon atom of the amide group. The electronic spectra of PA compound were studied in different polar and nonpolar solvents. The temperature effect on the electronic spectra confirms the presence of one conformer only. The hydrogen bonding and the orientation energies of the polar solvents were determined from the studies of mixed solvents. Complexes of PA with metal ions M(II) (Cu⁺⁺, Zn⁺⁺, or Fe⁺⁺) of ratio 2:1, respectively, were prepared, and their structure has been confirmed by elemental analysis, atomic absorption spectra, IR spectra, and ¹H‐NMR spectra. It has been concluded that the structure of the complexes has C_2h point group symmetry in which two PA molecules are chelated to any one of the metal ions Cu⁺⁺, Zn⁺⁺, and Fe⁺⁺.     

Orientational states of C60 molecule in crystals

Local symmetry of orientational states of the C₆₀ molecule in crystals has been investigated. It was shown that the various orientational phase transitions in different crystals are related to different orientational orbits. The model of orientational phase transitions based on a sequence of orientational states with different symmetry properties has been suggested. We have found that both the local symmetry of C₆₀ molecule and the symmetry of its internal vibrations become higher after a reduction of crystal spatial symmetry at the phase transition. This effect is fairly common and can be observed in the orientational order-disorder phase transitions with wave vectors at the Brillouin zone boundary. Feasible manifestations of the predicted effect in various experiments are discussed. Zh. éksp. Teor. Fiz. 113, 1081–1093 (March 1998)     

Theoretical study on the Cope rearrangement mechanisms and the homoaromaticity of semibullvalene,barbaralane, and 1,5‐methanosemibullvalene

Cope rearrangement mechanisms and the homoaromaticity of semibullvalene, barbaralane, and 1,5‐methanosemibullvalene in the ground and lowest excited states were studied by ab initio methods. In the ground state, the rearrangement reactions of semibullvalene and barbaralane occurred concertedly through the transition states with C_2v symmetry, and the transition states had a homoaromatic nature. In particular, the transition state of barbaralane exhibited the strongest homoaromaticity among the three systems treated here. On the other hand, for 7,8‐methanosemibullvalene, the structure with C_2v symmetry was not a transition state but one with a stable energy minimum. The energy minimum structure with C_2v symmetry had a biradical character. The lowest excited states of semibullvalene and barbaralane were the excitation to the σ* anti‐orbital, ¹B₂ and ¹B₁ states, and led to near di‐allyl states. The lowest excitation state of 1,5‐methanosemibullvalene had C_s symmetry and was the A″ state excitation in one side of two allyl parts. Copyright © 2011 John Wiley & Sons, Ltd.     

Infrared and Raman Spectra for Amino Group and C˭O Stretching Modes in Biomolecule 5‐Aminouracil

Abstract

Assuming planar geometry of 5‐aminouracil and C_s point group symmetry, it has been possible to assign all the 36 (25a′+11a″) normal modes of vibration. The two NH bonds of the NH₂ group appear to be non-equivalent as the NH₂ stretching frequencies and do not satisfy the empirical relation proposed for the two equivalent NH bonds of the NH₂ group due to their involvement and interaction with one hydrogen bond and the other adjacent oxygen atom of the parent molecule. The planar and nonplanar bending modes due to the C₄?O₈ bond are expected with have lower magnitude compared with those due to the C₂?O₇ bond.     

Permutation-inversion symmetry of C70 fullerite in the high-temperature phase

The permutation-inversion symmetry group of C₇₀ fullerite in its high-temperature phase is constructed with allowance for the rotation of its constituent molecules, and the local symmetry group of a rotating molecule in the crystal is identified. Irreducible representations of these groups are constructed that are compatible with the principle of wave-function symmetry with respect to permutations of identical nuclei. A group-theoretic classification is made of the quantum states of a rotating molecule and of the crystal in the high-temperature phase of C₇₀ fullerite. Selection rules are derived for electronic, vibrational, and rotational spectra in terms of irreducible representations of the permutation-inversion symmetry group of the crystal. Fiz. Tverd. Tela (St. Petersburg) 39, 1895–1901 (October 1997)     

Vibrational Spectra of Some Substituted Benzene Derivatives

Abstract

The infrared spectra of 1,2,3-; 1,2,4- and 1,3,5-trimethylbenzenes have been recorded in the liquid phase in the region 250–4000 cm^?1 on a Perkin Elmer Grating Spectrophotometer model 521. Under the general symmetry considerations, the molecule 1,2,4-belongs to C_2v point group, the 1,2,3-isomer belongs to Cs and the 1,3,5-isomer to D_3h point group. The observed bands have been assigned to different modes of vibrations.     

Vibrational spectra and rotational isomerism of allyl amine

The infrared spectra of allyl amine in the vapour, liquid and solid phases have been measured from 250 to 4000 cm⁻¹. The laser-Raman spectrum in the liquid state has also been recorded photoelectrically and qualitative depolarization measurements have been made. The interpretation of the spectral data suggests the presence of two rotational isomers (‘cis and trans”, and ‘ganche and trans’) in the vapour and liquid phases whereas the form having asymmetrical structure (‘gauche and trans’, C₁ symmetry) gets stabilized in the solid state at low temperature.     

Microwave spectrum and conformation of vinyl mercaptan: The syn rotamer

Rotational spectra of vinyl mercaptan (ethenethiol) CH₂CHSH and its isotopic modification CH₂CHSD have been studied by microwave spectroscpy. The molecule has been found to exist in two rotameric forms, syn and anti, associated with different orientations of the SH bond with respect to the vinyl framework. In this paper results are reported for the more stable syn form which is shown to be planar with ground state rotational constants A = 49 815.28(6) MHz, B = 5835.716(14) MHz, C = 5222.081(11) MHz, D_J = 2.85(17) kHz, D_JK = ?33.22(2.08) kHz, and δ_J = 0.425(65) kHz. Spectra have also been observed for the first and second excited states of the SH torsional vibration and the first excited state of the CCS angle bending mode. The dipole moment of the syn rotamer is μ_a = 0.813(1), μ_b = 0.376(4), and μ_total = 0.896(3) D.     

Angle-resolved polarization-dependent photoemission spectra of benzenethiol adsorbed on Cu(110)

Angle-resolved photoelectron spectra of benzenethiol chemisorbed on the Cu(110) face have been obtained with p- and s-polarized HeI (21.2 eV) radiation at room temperature. Comparison with the gas-phase spectrum and molecular-orbital correlation diagrams indicates that the benzenethiol bonds to the copper by way of the sulfur, rather than phenyl ring π-orbitals, and that the adsorption is dissociative, yielding a phenyl sulfide (mercaptide) surface species. An analysis of the polarization/angular dependence of the band intensities and comparison to symmetry-allowed transitions confirms that the molecule has the plane of the phenyl ring perpendicular to the surface. The assumed C_2v symmetry together with packing considerations further allows the orientation of the molecule and nature of the bonding to be suggested.     

Conformation,barrier to internal rotation,and structure of the PH2-group in phenylphosphine,studied by microwave spectroscopy

The microwave spectra of phenylphosphine (C₆H₅PH₂) and of mono- and dideuterated phenylphosphine (C₆H₅PHD and C₆H₅PD₂) were investigated. The two torsional sublevels of the vibrational ground state were assigned for each molecular species. Only μ_a-and μ_b-lines were observed, the μ_b-lines being split by approximately twice the splitting of the torsional sublevels. By means of internal rotation calculations with a program that determines the effective Hamiltonian for one top molecules without symmetry restrictions, the twofold barriers to internal rotation were determined to be 94.2 cm⁻¹ (C₆H₅PH₂), 91.1 cm⁻¹ (C₆H₅PHD), and 85.5 cm⁻¹ (C₆H₅PD₂). No effects due to inversion of the PH₂ group were observed in the spectra. For C₆H₅PH₂ and C₆H₅PD₂ the internal rotation potential is of the cos 2γ type with the minimum position corresponding to the configuration with the hydrogen atoms of the phosphine group on opposite sides of the phenyl ring plane, which is thus a plane of symmetry for the molecule. The C₆H₅PHD potential, however, contains an additional sin 2γ term with the effect of rotating the minimum 8.5° in the direction from D toward H. The direct monosubstitution method for determination of the hydrogen atoms of the PH₂ group gave inconsistent results, but the disubstitution method yielded a result comparable to the internal rotation calculation. The structural parameters determined for the PH₂ group are: PH = 1.414 Å, HPH = 94.27°, CPH = 97.29°, and tilt angle (CP to internal rotation axis) = 2.96° (P and H being on opposite sides of the internal rotation axis).     

Microwave spectrum,structure, and dipole moment of 7-oxabicyclo[2.2.1]heptane

The microwave spectrum of 7-oxabicyclo[2.2.1]heptane has been assigned in the ground and two excited vibrational states. Relative intensity measurements indicate that these two vibrations have wavenumbers of 120(30) and 330(30) cm^?1. The dipole moment obtained from Stark effect measurements is 1.621(10) D. The molecule is shown to have C_2v symmetry and the assignment of the two singly substituted ¹³C species gives the following skeletal structure: C₁-C₂ = 1.537(5) Å; C₂-C₃ = 1.551(5) Å; C₁-O = 1.452(10) Å; ?C₁OCC₄ = 95.3(10)° φ = 113.1(5)°.     

B2C(1A1)和BC2(2A′)的结构与解析势能函数

采用单双取代的二次组态相互作用方法，分别选用6-311++G(d,p)和6-311G(df,pd)基组，对B₂C和BC₂分子的结构进行了优化，得到这两个分子的基态结构为C_2v和C_s，基态电子状态为¹A₁和²A′，同时还得到了它们的平衡几何结构、离解能、谐振频率和力常数. 关键词： 碳化硼 Murrell-Sorbie函数 谐振频率 势能函数     

Vibrational spectroscopy and crystal structure analysis of two polymorphs of the di‐amino acid peptide cyclo(L‐Glu‐L‐Glu)

Cyclo(L ‐Glu‐L ‐Glu) has been crystallised in two different polymorphic forms. Both polymorphs are monoclinic, but form 1 is in space group P2₁ and form 2 is in space group C2. Raman scattering and FT‐IR spectroscopic studies have been conducted for the N,O‐protonated and deuterated derivatives. Raman spectra of orientated single crystals, solid‐state and aqueous solution samples have also been recorded. The different hydrogen‐bonding patterns for the two polymorphs have the greatest effect on vibrational modes with N H and CO stretching character. DFT (B3‐LYP/cc‐pVDZ) calculations of the isolated cyclo(L ‐Glu‐L ‐Glu) molecule predict that the minimum energy structure, assuming C₂ symmetry, has a boat conformation for the diketopiperazine ring with the two L ‐Glu side chains being folded above the ring. The calculated geometry is in good agreement with the X‐ray crystallographic structures for both polymorphs. Normal coordinate analysis has facilitated the band assignments for the experimental vibrational spectra. Copyright © 2009 John Wiley & Sons, Ltd.     

Microwave spectrum of tropone

The microwave spectrum of tropone (2,4,6-cycloheptatriene-1-one) has been obtained and assigned. The observation of a statistical weight intensity alternation indicates that the molecule has C_2v symmetry. Relative intensity measurements show the molecule to possess a low wavenumber vibration whose 1-0 interval is 60 ± 20 cm^?1. The dipole moment is found to be 4.1 ± 0.3 D by the “rate-of-growth” method.     

The photoelectron and absorption spectra of allyl halides

The ultraviolet photoelectron spectra (5–20 eV) absorption spectra (1400–2500 Å) of allyl C₃H₅X (X = F, Cl, Br, I) have been measured. The ionisation potentials between 5–16 eV are determined and the type of orbital is interpreted with the aid of the vibration pattern and the band form.From these spectra several conclusions can be drawn concerning the iodide: (1) the ionisation potential of the π_C_C system of allyl iodide is lower than expected when compared to the ionisation potential of the corresponding band of the other halides. (2) The splitting of its np lone pair photoelectron bands is not in accordance with the expected splitting associated with spin-orbit coupling. (3) One of the two components of the lone pair bands has been broadened. These observations can be explained by a through-space interaction of one of the iodine “lone pairs” with the π-system.