The infrared spectra and conformation of methyl and ethyl propenyl ethers

The infrared spectra of the cis and trans geometric isomers of methyl and ethyl propenyl ethers have been recorded in the liquid and vapour phase, in the region 4000-200 cm^?1. Solid phase spectra have also been recorded for all but trans methyl propenyl ether. Evidence is given for the existence of two rotameric forms for both the trans compounds, in each case the more stable conformer being planar s-cis; but a single non-planar conformation is suggested for the two cis isomers. The enthalpy difference between the two rotameric forms in trans ethyl propenyl ether was found to be 4.6 ± 1.0 kJ mol^?1 (1100 ± 250 cal mol^?1).     

Infrared studies of rotational isomerism in α-halogeno-acetamides

Infrared spectra of fluoroacetamide, chloroacetamide, and iodoacetamide have been recorded in the solid, liquid, and vapour phases in the region 4000–200 cm^?1. A complete vibrational frequency assignment of the fundamental and non-fundamental bands has been made for each of these molecules. The results show that each of these compounds exists as an equilibrium mixture of gauche and trans isomers. Enthalpy differences (ΔH) between these isomers were calculated for each of these compounds in the liquid and vapour phases. The trans form is the most stable of the rotational isomers in all three phases.     

Conformational structure of N-methylpropionamide and N-methylisobutyroamede. NMR shift reagent and IR study

The structures of the stable conformers of N-methyjpropionamide and N-methyliso-butyroamide in CCl₄, solution were determined by a combination of IR spectroscopy and NMR spectroscopy with lanthanide shift reagents. N-methyl-propionamide was found to exist in the form of two rotational isomers, 1 and 2, with the ethyl group twisted out of the plane of the amide bond by the angles Ψ = 140 and 20°, respectively. For these two conformers, the enthalpy difference is ΔH = 2.13 ± 0.08 kcal mole^?1 and the entropy difference ΔS = 7.81 ± 0.55 cal mole^?1 grad^?1. N-methylisobutyroamide exists in a single form, with the two C-methyl group positions very close to those found in the two isomers of N-methylpropionamide.     

Rotational isomerism in 1,4-disilabutane

Raman spectra of 1,4-disilabutane (DSB) are recorded in both liquid and solid states. IR spectra in the gas and solid phases are also recorded. Two rotational isomers, trans and gauche, are present in the gas and pure liquid phases. An assignment of the main features of the IR and Raman spectra is made, with the aid of normal coordinate calculations for the two isomers. The temperature dependence of the Raman spectrum of DSB is studied in the range 77–300 K. The enthalpy difference between the two isomers is 5.01 ± 0.31 kJ mol^?1. This value is expected to be higher for gaseous DSB.     

The vibrational spectra and rotational isomerism of 1,1,1-Trimethoxyethane

The liquid, vapour and solid-state infrared spectra of 1,1,1-trimethoxy-ethane were recorded in the region 250–4000 cm⁻¹. The laser-Raman spectrum with qualitative depolarization data was obtained for liquid only. The spectra show that there are at least two rotational isomers present in the liquid phase. The solution spectra reveal that the less polar form is the more stable in the liquid phase. The form playing an important role has GGG configuration. A vibrational assignment has been attempted for the observed infrared and Raman bands.     

Vibrational spectra and rotational isomerism of triallyl amine

The infrared spectra of triallyl amine in the vapour and liquid phases (as solutions in CS₂, CCl₄, CH₃Cl and CH₃CN), and in the solid state at low temperature were measured from 250 to 4000 cm⁻¹. The Raman spectrum of the liquid was recorded and qualitative depolarization measurements were made. It is shown that in the liquid and vapour phases the molecule exists as a mixture of at least two rotational isomers, while in the crystalline phase it assumes a single configuration having point-group symmetry C₃. A vibrational assignment for the observed bands in the infrared and Raman spectra is proposed on the basis of the C₃ point group symmetry for the more stable form of the molecule.     

Microwave spectrum of ethynyl-cyclohexane

The ground state microwave rotational spectra of the axial and equatorial chair forms of ethynyl-cyclohexane are investigated in the frequency region 8–26.5 GHz. The spectrum of the first vibrationally excited state of the e-conformer is also assigned and intensity measurements locate this state at 130 ± 30 cm^?1. Using the ground state rotational constants obtained for the two isomers, a least-squares structural analysis is performed.     

Conformational analysis of N-methyl-m-fluoroaniline by microwave spectroscopy

Conformational analysis of N-methyl-m-fluoroaniline has been performed by low resolution microwave spectroscopy. Two rotational isomers, corresponding in a near-planar configuration to the m-fluorine being either cis or trans with respect to the amino hydrogen, have been detected. The energy difference is found to be 270 ± 70 cal mol^?1, the cis isomer being the more stable. Ab initio calculations indicate a barrier height for the internal rotation of the HNCH₃ group around the C_ph—N bond of 9.04 kcal mol^?1.     

Neutron inelastic scattering spectra and phase transition of 1,2-dichloroethane crystal

Neutron inelastic scattering spectra of 1,2-dichloroethane crystal have been measured at three temperatures above and below 177°K where the crystal undergoes a broad phase transition. Two and three peaks have been observed in the high and low temperature phases, respectively. The frequency distribution g(v) has been calculated in the first Brillouin zone for the low temperature phase and is compared with the observed spectra. The results show that the phase transition at 177°K is associated with rotational motion of the molecule around the axis passing through two chlorine atoms.     

Darstellung und Konformationsuntersuchungen von cis- und trans-Isomeren des 1,2,4,5-Tetramethyl-3,6-diphenoxy-3,6-dithioxo-1,2,4,5-tetraaza-3,6-diphosphacyclohexans

Synthesis and Conformational Analysis of Cis- and Trans-Isomers of 1,2,4,5-Tetramethyl-3,6-diphenoxy-3,6-dithioxo-1,2,4,5-tetraaza-3,6-diphosphacyclohexane A mixture of isomers of the title compound could be prepared in much better yields (up to ca. 25%) by the reaction of bis(1,2-dimethylhydrazido) thiophosphoric acid O-phenylester with phenoxythiophosphoryl dichloride in the presence of triethylamine and aluminum chloride as catalyst. Separation of cis- and trans-isomers was achieved by sorting of crystals or in low yields by fractional crystallization. ³¹P- and mainly ¹H-NMR investigations at different temperatures show, that in both isomers the saturated sixmembered ring has a twist-conformation in which sulfur and phenoxy substituents located cis or trans respectively adopt the isoclinal positions. The isomers reveal remarkably different barriers of activation for the interconversion of two enantiomeric twist forms (cis ΔG^# = 63 ± 1 kJ/mol; trans 47 ± 1 kJ/mol).     

Microwave spectrum of 3-nitrothiophene

The microwave spectrum of 3-nitrothiophene has been studied in the frequency region 26.5–40.0 GHz. The rotational transitions of the ground state and the first six torsionally excited states have been assigned. The ground state rotational constants have been determined to be A_o=4622.61 ± 0.07 MHz, B_o = 1231.751 ± 0.001 MHz and C_o = 973.062 ± 0.001 MHz. The planarity of the molecule has been demonstrated. The first torsional frequency and the barrier to internal rotation of the nitro group have been estimated as 60 cm^?1 and 3.8 kcal/mole, respectively.     

Molecular conformations of methyl formate and methyl vinyl ether from ab initio molecular orbital calculations

Ab initio molecular orbital theory with minimal and extended basis sets and a flexible rotor geometric model has been used to investigate the rotational potential surfaces of methyl formate and methyl vinyl ether. For both molecules, the most stable structures (IA and IIA, respectively) are planar cis; additional potential minima are found which correspond to planar trans structures (IB and IIB). The latter lie respectively about 4—8 and 1—2 kcal mol^?1 above the corresponding cis rotational isomers. Methyl rotational barriers have been determined for cis and trans structures of each molecule. For trans methyl formate, there is a slight but unexpected preference for an eclipsed arrangement of the methyl group.     

Selective separation of silver(I) and mercury(II) ions in natural water samples using alumina modified thiouracil derivatives as new solid phase extractors

A simple and reliable solid-phase extraction (SPE) method has been developed to synthesise two new sorbents: 6-propyl-2-thiouracil and 5,6-diamino-2-thiouracil physically loaded onto alumina surface, phases I and II, respectively. The synthesis of these new phases has been confirmed by IR-spectroscopy. The surface concentrations of the organic moieties were determined to be 0.182 and 0.562 mmol g^?1 for phases I and II, respectively. The evaluation of the selectivity and metal uptake properties incorporated in these two alumina phases were also studied and discussed for 10 different metal ions: Ca(II), Fe(III), Co(II), Ni(II), Cu(II), Zn(II), Cd(II), Hg(II), Pb(II) and Ag(I) under different controlling factors. The data obtained clearly indicated that the new SP-extractors have the highest affinity for retention of Hg(II) ions. Selective separation of Hg(II) from Ag(I) as one of the most interfering ion, in addition to the other eight coexisting metal ions under investigation, was achieved successfully using the new sorbents at pH = 9.0 under static conditions. Therefore, Hg(II) exhibits major retention percentage (100.0%) using phase I or II. However, Ag(I) exhibits minor retention percentage equal to 1.33% using phase I and 0.67% using phase II. On the other hand, the retention percentage of the other eight metal ions ranged (0.0–3.08%) using phase I and (0.0–1.54%) using phase II at the same pH. The new phases were applied for separation and determination of trace amounts of Hg(II) and Ag(I) spiked natural water samples using cold vapour atomic absorption spectroscopy and atomic absorption spectroscopy with no matrix interference. The high recovery values of Hg(II) and Ag(I) obtained using phases I and II were ranged 98.9 ± 0.1–99.2 ± 0.05% along with a good precision (RSD% 0.01–0.502%, N = 3) demonstrate the accuracy and validity of the new sorbents for separation and determination of Hg(II) and Ag(I).     

Reaction of O(3P) atoms with nitromethane vapour at 295 K

The reaction of O(³P) atoms with nitromethane vapour in a discharge flow system is found to have a stoichiometry of 7.6 ± 0.3:1 respectively and initial step rate constant of (1.9 ± 0.3) × 10⁶ dm³ mol^?1 s^?1 at 295 K. Addition of carbon monoxide confirmed that approximately three OH radicals are produced per cycle.     

Microwave and far-IR spectra,conformational stability,molecular structure,barriers to internal rotation and ab initio calculations for the anticlinal conformer of trans-1-fluoro-2-butene

The microwave spectrum of trans-1-fluoro-2-butene, trans-(CH₃)HCCH(CH₂F), has been recorded in the region of 18.0–39.0 GHz. Both a-type R- and b-type Q-branch assignments have been made for the ground and first two vibrationally excited states of the asymmetric torsion for the gauche (anticlinal) conformer. The ground state rotational constants for this conformer are found to have the following values: A = 19,938.33±0.48, B = 2071.37±0.01, C = 2022.17±0.01 MHz. From an analysis of the internal rotational splittings of the Q-branches, the three-fold rotational barrier for the methyl group is determined to be 596±7 cm⁻¹ (1.70±0.02 kcal/mol). From the Stark effect the dipole moment components for the gauche conformer were determined to be |μ_a| = 1.86±0.01, |μ_b| = 1.16±0.01, |μ_c| = 0.31±0.05, and |μ_t = 2.21±0.01 D. The fundamental asymmetric torsion for the cis (synclinal) conformer has been observed in the far-IR spectrum of the vapor at 123.95 cm⁻¹ whereas that for the gauche conformer has been determined to occur at 82.8±5 cm⁻¹ based on relative intensity measurements obtained from the microwave spectrum. From these data the potential function which governs the internal rotation of the asymmetric top has been determined and the following potential constants have been evaluated: V₁ = −191±10, V₂ = 598±10, V₃ = 786±13, V₄ = 59±5, and V₆ = 79±5 cm⁻¹. These data are consistent with the more stable conformer having the fluorine atom cis (synclinal) to the double bond and lying 300±33 cm⁻¹ (858±94 cal/mol) lower in energy than the gauche rotamer. Utilizing ab initio calculations with the MP2/6-31G* basis set and the three rotational constants, r₀ structural parameters are estimated. Also, the barriers to conformer interconversion have been calculated with the RHF/3-21G, RHF/6-31G*, and MP2/6-31G* basis sets. All of these results have been compared to the similar quantities of some corresponding molecules.     

Production of chiral matrices with hybrid silver–thiocholesterol nanosystems and study of their properties

A new type of chiral matrix based on silver–thiocholesterol hybrid nanosystems adsorbed on silica gel has been proposed. The molar ratio of stabilized thiocholesterol (L) ligand and silver (Ag) was found to have little effect on the size of the resulting silver nanoparticles (SNPs). The average diameter of SNPs was 2.7 ± 0.4, 2.2 ± 0.4, and 2.1 ± 0.6 nm upon the ratios Ag: L = 1: 5, Ag: L = 1: 2, and Ag: L = 1: 0.5, respectively. The resulting chiral matrices possess enantioselectivity relative to the 1,1’-binaphthyl-2,2’-diamine (BNDA) and trifluoroanthranyl ethanol (TFAE) optical isomers. The TFAE optical isomers were successfully separated using thin layer chromatography (α = 1.56).     

Chemical equilibria 6. Measurement of equilibrium constants for the dehydrogenation of 2-methylpropan-1-ol by a vapour-flow technique

Equilibrium constants for 2-methylpropan-1-ol + 2-methylpropanal + hydrogen have been calculated from measurements of the composition of mixtures formed by passing the vapour over a catalyst at several temperatures in the range 473 to 563 K. Equations relating the changes in enthalpy and entropy of the dehydrogenation reaction to temperature were derived from the equilibrium constants with the aid of heat capacities. By coupling these changes with other thermodynamic data, the standard enthalpy of formation and the standard entropy of 2-methylpropanal at 298.15 K were calculated to be ?(215.7 ± 1.3) kJ mol^?1 and (331.2 ± 1.7) J K^?1 mol^?1 respectively, in the gas state, and ?(247.3 ± 1.8) kJ mol^?1 and (238.3 ± 4.4) J K^?1 mol^?1 respectively, in the liquid state.     

Energy levels of gaseous magnesium monoxide and the bond dissociation energy

Absorption and emission spectra of gaseous magnesium monoxide produced by shock-heating MgO particles suspended in Ar/O₂ mixtures have been studied as a function of temperature. The green B¹Σ⁺ -X¹Σ⁺ system has been observed in absorption for the first time and the X state is found to lie lower by 3200 ± 1000 cm^?1 than the lower state of the strong ultraviolet system at 372.1 nm which is attributed to a triplet-triplet transition in MgO. A strong continuum has been observed in absorption by MgO vapour. A discussion of the bond dissociation energy of MgO is given which suggest that the appropriate value D⁰₀ (MgO) = 390± 35 kJ mol^?1.     

1H NMR study of isomerization in chlorotin(IV) ternary complexes of 8-quinolinol and 5,7-dichloro-8-quinolinol

A complete analysis of the temperature dependence (?30 to 52°C) of the ¹H NMR spectra in d-chloroform of the ternary complexes, bis-(8-quinolinato)tin(IV) dichloride and bis-(5,7-dichloro-8-quinolinato)tin(IV) dichloride has been performed. The intramolecular character of the exchange process has been established, and the spectra have been analyzed by the total lineshape method in terms of the interconversion of two isomers, the cis-cis-trans and the cis-trans-cis (with respect to Cl, N and O atoms), including the tin-proton couplings in the simulations. Arrhenius parameters of the process were E_a = 54 ± 1 and 52 + 1 kJ mol^?1, and log A = 11.8 ± 0.2 and 11.7 ± 0.3, respectively, for the two complexes. The similarity of the activation parameters obtained for both complexes indicates that the presence of bulky Cl atoms in the 8-quinolinol ring had no appreciable energetic influence on the isomerization process. Data were compared with those reported for other chlorinated hexacoordinated complexes, involving ligands other than the 8-quinolinol ring.     

Microwave spectrum and structure of CF3OOCl

The microwave spectrum of chloroperoxytrifluoromethane has been recorded from 12.5 to 40.0 GHz. Only a-type transitions were observed. The R-branch assignments have been made for both the CF₃OO³⁵C1 and CF₃OO³⁷Cl species for the ground vibrational state. The rotational constants are: A=4808± 12, B=1318.55±0.02, C=1278.28±0.02 MHz for the ³⁵CI species, and A=4748±300,B=1285.28±0.96, C=1246.80±0.96 MHz for the ³⁷Cl species. From a diagnostic least-squares adjustment to fit the six rotational constants the following structural parameters were obtained: r(C-0)=1.377±0.03 Å, r(O-O)=1.445± 0.049 Å, r(Cl-O)=1.69±0.04 Å, ∠COO=108.1±4.2°, ∠ClOOC=99.5±2.0°, and ∠tilt = 6.0±0.9° with reasonable assumptions for the three other structural parameters. The relatively large uncertainty in these structural parameters results from the large uncertainty in the A rotational constants. These parameters are compared to the corresponding ones in some other peroxides. The quadrupole coupling constants have been obtained and are discussed.