The geometry of organophosphonates: Fourier-transform microwave spectroscopy and ab initio study of diethyl methylphosphonate, diethyl ethylphosphonate, and diisopropyl methylphosphonate

The rotational spectra of diethyl methylphosphonate (DEMP), diethyl ethylphosphonate (DEEP), and diisopropyl methylphosphonate (DIMP) in supersonic expansions have been acquired using Fourier-transform microwave spectroscopy. Spectroscopic constants have been determined for five distinct conformers of the three molecules. Experimental data have been compared to ab initio calculations performed for each species. For both DEMP and DEEP, the calculations indicate the presence of several low-energy conformers (i.e., ?∼400 cm⁻¹ above the ground state) may be present at room temperature (300 K) for both DEMP and DEEP. When entrained in a supersonic expansion, the rotational temperatures of the samples are much colder (∼2 K); nonetheless, spectra from three conformers of DEEP are still observed experimentally, whereas only one conformer of DEMP is observed. In contrast, only a single low-energy conformer of DIMP is predicted by theory, and is present in the molecular beam. The relative abundance of low-energy conformers of DEMP and DEEP is attributed to the flexibility of the ethoxy groups within each molecule. The presence of multiple DEEP conformers in the supersonic beam indicates a more complex potential energy surface for this molecule that is directly related to conformational shifts of the PCH₂CH₃ group. Conversely, the absence of low-energy conformers of DIMP is attributed to steric hindrance between isopropoxy groups in the molecule. The internal rotation barrier for the PCH₃ group in DEMP and DIMP is compared to that found in DMMP and several phosphonate-based chemical weapon agents.     

Effect of zinc salt on transport,structural, and thermal properties of PEG-based polymer electrolytes for battery application

Solid polymer polyethylene glycol (PEG)-based electrolytes composed with zinc acetate Zn(CH₃COO)₂ have been prepared by using solution blending. We proposed a scheme of PEG–zinc acetate for battery application. The structure confirmation was done by using X-ray diffraction studies detecting the phase variation. The thermal properties demonstrate the optimization of melting point (T _m) as a function of loading zinc acetate. The impedance analysis reveals that the role of ionic conductivity depends on the controlled concentration of Zn(CH₃COO)₂. Optimum ionic conductivity σ?~?1.55?×?10^?6 S?cm^?1 at room temperature (303 K) was observed for 70:30 composition. The linear variation in log σ vs 1000/T plot is based on the Arrhenius-type thermally activated process. The simultaneous discharge profile was confirmed by the solid-state electrochemical cell. Hence, the PEG–zinc acetate composition was suggested for polymer electrolyte battery application.     

Microwave spectrum and rotational isomerism in isopropyl mercaptan

A microwave investigation of isopropyl mercaptan has established the existence of both trans and gauche conformers, the trans being more stable by 57 cal mole^?1. Stark effect measurements give the dipole moments as 1.61 ± 0.2 D for the trans and 1.53 ± 0.2 D for the gauche species. The spectra of the isotopic species (CH₃)₂CH³²SD, (CH₃)₂CH³⁴SH, and (CH₃)₂CH³⁴SD of the trans form have also been analyzed, providing a limited amount of structural data.The rotational spectrum of the gauche isomer is noticeably influenced by inversion. Interactions between energy levels in the two lowest inversion states have been satisfactorily accounted for in terms of rotational constants, coupling parameters (G_a and G_c), and ΔE₀, the inversion level splitting. ΔE₀ is found to be 562.4 MHz for the ground state of (CH₃)₂CHSH and 10.0 MHz for (CH₃)₂CHSD. A value of 1.98 kcal mole^?1 has been calculated for the barrier to internal rotation of the -SH group in terms of a V₃ potential.     

Two conformers of ethyl pivalate studied by microwave spectroscopy

The rotational spectra of two conformers of ethyl pivalate, (CH₃)₃C-COO-C₂H₅ have been recorded by molecular beam FT microwave spectroscopy. The analysis yielded a set of three rotational constants and five quartic centrifugal distortion constants for each conformer. The conformers were identified by comparing the experimental rotational constants with those obtained by ab initio calculations at MP2/6-311++G∗∗ level. One conformer has C_s symmetry, the other one forms a pair of enantiomers with C₁ symmetry. Additionally, the torsional potentials of the tert-butyl group and of the methyl groups were obtained by ab initio methods.     

Infrared spectra of CH3Br: The 2ν2 band near 2600 cm−1

The rotational fine structure of 2ν₂ has been studied under high resolution (0.03 cm^?1) for CH₃⁷⁹Br and CH₃⁸¹Br. About 700 lines have been assigned for each isotopic species. The band centers have been found at 2596.871 and 2596.815 cm^?1, respectively.     

ESR of gamma irradiated single crystals of cholesteryl acetate and cholesteryl chloroformate

Cholesteryl acetate and cholesteryl chloroformate compounds have been irradiated with ⁶⁰Co-γ rays at room temperatures. The irradiated samples have been examined for paramagnetic resonance, and the observed spectra in several cases have been identified with specific radicals. The results in each case have been considered in relation to the present knowledge of the radiation chemistry of the compound. The single crystals have been investigated between 120 and 300?K. The spectra are found to be temperature independent and radiation damage centers are attributed to ?HCH₂ radical for cholesteryl acetate and ?H₃ and ?HCH₂ CH₂ CH₂ radicals for cholesteryl chloroformate.     

The microwave,Raman, far infrared,and NMR spectra and structure of methylchloroformate

The microwave spectra of six isotopic species of methylchloroformate, ClCO₂CH₃, have been recorded from 18.0 to 40.0 GHz. Structural parameters have been determined, and it is shown that the only stable conformer at ambient temperature is the s-trans. The Raman and far infrared spectra of the vapor are reported. Four cases of Fermi resonance have been observed in the Raman effect. Both the methyl and methoxy torsions have been observed in the far infrared, and the methyl barrier to internal rotation has been determined to be 1.15 kcal/mole (1.19 kcal/mole for the CD₃ rotor), which is in agreement with the 1.23 kcal/mole obtained from the microwave splitting method. It is shown from both the ¹³C and ¹H NMR spectra along with the far-infrared data that only one conformer exists, which is contrary to what was previously reported. The vibrational spectrum of the solid is also reported and discussed.     

Microwave spectrum,dipole moment,and structure of anti-vinyl alcohol

The rotational spectra of the anti conformer of vinyl alcohol (ethenol, H₂CCHOH) and its OD modification have been studied by microwave spectroscopy. The compounds have been generated by very-low-pressure pyrolyses of the appropriate isotopic species of 3-thietanol. In both cases the 25 measured μ_a- and μ_b-type transitions allowed the rotational constants and all five quartic centrifugal distortion constants to be determined. Stark effect measurements have yielded the electic dipole moment: μ_a = 0.547(2), μ_b = 1.702(1), and μ = 1.788(1) D. By relative intensity measurements it has been found that the vibrational ground state of the anti conformer lies 4.5±0.6 kJ mol^?1 above the syn conformer. In addition, ab initio calculations at the 6–31G⁷ level have been performed to obtain the structure, relative energy, and dipole moment of both rotamers.     

The microwave spectrum, structure, and barrier to internal rotation of selenoacetaldehyde, CH3CHSe

The rotational spectrum of the unstable molecule selenoacetaldehyde, CH₃CHSe, has been studied by microwave spectroscopy between 26.5 and 40 GHz. Transitions have been measured for five abundant selenium isotopic variants. These measurements have, together with structural information from the related molecules CH₃CHS and CH₃CHO, allowed reliable data on the C=Se bond length (1.758 ± 0.01 Å) and the e angle (125.7 ± 0.3°) to be derived. The spectral lines show splittings due to hindered internal rotation and using these together with the derived structure, barrier heights of 1602 cal mole⁻¹ (6703 J mole⁻¹) and 1648 cal mole⁻¹ (6859 J mole⁻¹) have been determined for the ground and first torsionally excited states, respectively.     

Structure and rotational dynamics of methyl propionate studied by microwave spectroscopy

We report on the rotational spectra of the most abundant conformer of methyl propionate, CH₃CH₂COOCH₃, recorded with a Fourier transform microwave spectrometer under molecular beam conditions. We present accurate rotational constants and centrifugal distortion constants. For the propionyl CH₃ CH₂CO– methyl group and the methoxy –OCH₃ methyl group, barriers of 820.46(99)?cm^?1 and 429.324(23)?cm^?1, respectively, were found. For spectral analysis, two different computer programs were used, the code BELGI-C_s-2tops based on the rho axis method (RAM) and the code XIAM based on the combined axis method (CAM). The results are compared. The experimental work was supplemented by quantum chemical calculations. Potential energy functions for the rotation of the terminal methyl groups and also of the entire ethyl group were parametrized.     

Low barrier methyl rotation in 3-pentyn-1-ol as observed by microwave spectroscopy

ABSTRACT

The rotational spectrum of 3-pentyn-1-ol, CH₃?C≡C?CH₂CH₂OH, was measured using a molecular beam Fourier transform microwave spectrometer operating in the frequency range from 2 to 26.5 GHz. A two-dimensional potential energy surface was calculated at the MP2/6-311++G(d,p) level of theory for a conformational analysis, yielding five conformers. The most stable conformer exhibits C₁ symmetry and was assigned in the spectrum by comparison with the results from quantum chemical calculations. The barrier to internal rotation of the propynyl methyl group CH₃?C≡C? was found to be only 9.4552(94) cm^?1. Molecular parameters and internal rotation parameters could be accurately determined using the program xiam and belgi-C₁. The internal rotation barrier was compared with those of other molecules containing a propynyl methyl group.     

From quantum chemistry to dissociation kinetics: what we need to know †

The relationship between rate constants for dissociation and the reverse association reactions and their potential energy surfaces is illustrated. The reaction systems e^? + SF₆ ? SF₆ ^? →SF₅ ^? + F, H + CH₃ ?CH₄, 2 CF₂ ? C₂F₄, H + O₂ →HO₂, HO + O ?HO₂ ? H + O₂, and C + HO →CHO are chosen as representative examples. The necessity to know precise thermochemical data is emphasised. The interplay between attractive and anisotropic components of the potentials influences the rate constants. Spin–orbit and electronic–rotational coupling in reactions between electronic open-shell radicals so far generally has been neglected, but is shown to have a marked influence on low temperature rate constants.     

Microwave spectrum,conformation, and quadrupole coupling constants of cyclopentyl chloride

The microwave spectra of the normal and two isotopic species of cyclopentyl chloride have been observed and analyzed. For the normal isotopic species the rotational constants (in MHz) are A = 4547.77 ± 0.01, B = 2290.22 ± 0.01, and C = 2073.34 ± 0.01. From the rotational constant data, it has been shown that the stable molecular conformation is the bent axial form. Quadrupole coupling constants have been measured for the ³⁵Cl nucleus, the values being (in MHz) χ_aa = ?23.70 ± 0.10, χ_bb = 32.33 ± 0.36, and χ_cc = ?8.63 ± 0.37. When transformed to the CCl bond axis system, the coupling constants confirm the axial structure. Extensive vibrational satellite structure, presumably arising from the pseudorotational ring mode with a fundamental frequency of 52 ± 5 cm^?1, has been observed and assigned. No spectral evidence has been observed for a second stable molecular conformer.     

A new study of the ν 2(A 1) infrared band of phosphorus trifluoride

The high-resolution Fourier transform infrared spectrum of phosphorus trifluoride (PF₃) has been reinvestigated in the v_2?=?1 vibrational excited state near 487?cm^?1 (at a resolution of 3?×?10^–3?cm^–1). Thanks to our new accurate rotational ground-state C ₀ value, 0.159970436(69)?cm^–1, and to recent pure rotational measurements, 318 new infrared transitions of the ν ₂ fundamental band have been assigned, extending the rotational quantum number values up to K _max?=?71 and J _max?=?72. A merge, for the first time, of 135 reported microwave data (K _max?=?42 and J _max?=?49) within the v_2?=?1 excited level and 2860 rovibrational transitions yielded improved constants of ν ₂. Parameters of this band have been obtained, up to sextic centrifugal distortion constants, by least-squares fits, σ _IR?=?3.60?×?10^–4?cm^–1 and σ _MW?=?5.53?×?10^–6?cm^–1 (166?kHz). Comparison of these constants with those measured previously by infrared spectroscopy reveals orders of magnitude higher accuracy of these new values.     

Millimeter wave free-jet spectrum of vinyl acetate

The rotational spectrum of vinyl acetate has been assigned and measured by millimeter wave absorption free-jet spectroscopy. Only lines of the most stable conformer, the one with the carbonyl oxygen cis with respect to vinyl group and the terminal vinyl carbon trans with respect the acid group, have been observed. The observed species is the most stable one, according to theoretical calculations at the MP2(full)/6-311++G∗∗ level of theory. All rotational lines are split by internal rotation of the methyl group; the value of the barrier for this motion was determined to be V₃ = 1.855(1) kJ mol⁻¹.     

Microwave spectrum,conformation, quadrupole coupling constants,and barrier to internal rotation of methoxyamine

The microwave spectra of three isotopic species of methoxyamine (CH₃ONH₂) have been studied. For the normal species the ground-state rotational constants are A = 42488 ± 150 MHz, B = 10049.59 ± 0.03 MHz, and C = 8962.85 ± 0.03 MHz. From these data and those from the -NHD and -ND₂ species, the amino protons have been shown to occupy a symmetrical trans position relative to the methyl group. The barrier to internal rotation of the methyl group has been found to be 873 ± 15 cm^?1 by analysis of ground-state splittings. Analysis of hyperfine splittings has yielded the ¹⁴N quadrupole coupling constants, which have the following values for the normal isotopic species: χ_aa = 3.63 ± 0.03 MHz, χ_bb = ?3.69 ± 0.07 MHz, and χ_cc = 0.06 ± 0.07 MHz.     

Composition,temperature and radiation induced changes in gamma irradiated AAAMPS copolymer

Effect of composition, temperature and radiation dose in gamma irradiated acrylamide-2-acrylamido-2-methyl propane sulphonic acid (AA) copolymer has been investigated by electron spin resonance (ESR) and fourier transform infrared (FTIR) techniques. ESR spectra of gamma irradiated AA copolymer have been recorded under different conditions. The observed ESR spectra are analysed by computer simulation techniques, to separate the constituent component spectra. Magnetic parameters employed to simulate the component spectra enabled the identification of corresponding free radicals. The AA copolymer with low acrylamide content composed of macroradicals of the type ?CH₂?CH?CH₂? and methyl radicals (CH₃) whereas the copolymer with high acryl amide content possess methyl radicals and radicals of the type ?CH₂?C(CONH₂)?CH₂?/CH₃?C?CH₃. Reasons for the variation in the formation of free radicals have been explained. The observed changes in ESR spectra of irradiated AA copolymer at higher temperatures are thought to be due to the recombination of free radicals. Formation of free radicals found to be enhanced with the increase in dose of irradiation. FTIR spectra of pure and irradiated copolymers have also confirmed the previous results.     

Conformational,vibrational, and structural studies of 2,2,3,3,3‐pentafluoropropylamine from Raman and infrared spectra of gas,liquid, xenon solutions,and solid supported by ab initio calculations

The Raman and infrared spectra (3500–50 cm⁻¹) of the gas, liquid or solution, and solid were recorded of 2,2,3,3,3‐pentafluoropropylamine (CF₃CF₂CH₂NH₂) and the ND₂ isotopomer. Variable temperature (−55 to − 100 °C) studies of the infrared spectra (3600–400 cm⁻¹) of samples dissolved in liquid xenon have been carried out. From these data, two of the five possible conformers have been identified and their relative stabilities obtained. The enthalpy difference was determined between the more stable Tt conformer and the less stable Tg form to be 280 ± 14 cm⁻¹ (3.35 ± 0.17 kJ/mol). The first indicator is the NCCC dihedral angle (G = gauche or T = trans), and the second one (g = gauche or t = trans) is the relative position of the lone pair of electrons on nitrogen with respect to the β‐carbon. The percentage of the Tg conformer at ambient temperature is estimated to be 34 ± 2%. The conformational stabilities have been predicted from ab initio calculations utilizing several different basis sets up to aug‐cc‐pVTZ for both MP2(full) and density functional theory calculations by the B3LYP method. Vibrational assignments have been provided for most of the observed bands for both isotopomers, supported by MP2(full)/6‐31G(d) ab initio calculations to predict the harmonic force fields, wavenumbers, infrared intensities, Raman activities, and depolarization ratios for both conformers. Estimated r₀ structural parameters were obtained from adjusted MP2(full)/6‐311 + G(d,p) calculations. The results are discussed and compared with the corresponding properties of some related molecules. Copyright © 2011 John Wiley & Sons, Ltd.     

The Dualistic Nature of -NH3 +, A weak π-Donating,Strong σ-Withdrawing Substituent. Effects on the Intensity of the UV Spectra of the Toluidinium Ions and Related Molecules

Abstract

Hyperconjugation is not restricted to alkyl groups^(1–4) and ammoniums interact with π systems through σ-π hyperconjugative coupling^(5–9). Their influence on the UV spectrum of the secondary transition of the benzene chromophore in anilinium ions has only been studied during the last years. Previously it was assumed without enough experimental support, that ammonium groups have no spectroscopic effects on a π chromophore (for example:^(10,11)). In fact, although it is a strong σ-electronwithdrawing substituent, an ammonium group is a π-donating one ^5–8). Its π-donating ability - contrary to what is observed in the corresponding alkyl groups where N is replaced by C - increases whenever the number of N⁺?C bonds increases, and ?N(CH³)³+ could be as much π-donating as the ?C(CH₃)₃ group for pseudo-free molecules⁽⁵⁾.     

New measurements and global analysis of chloromethane in the region from 0 to 1800 cm

New high resolution Fourier transform spectra of pure ¹²CH₃³⁵Cl and ¹²CH₃³⁷Cl isotopomers of chloromethane have been recorded in Wuppertal covering the region from 600 to 3800 cm⁻¹. New rotational transitions within the v₂=1, v₅=1, and v₃=2 states have been measured at Lille. A first global analysis of the lower four band systems of the molecule (700-1800 cm⁻¹) is reported. The model was based on an effective Hamiltonian and dipole moment expressed in terms of irreducible tensor operators. A common set of 125 effective hamiltonian parameters (sixth order) has been adjusted to fit simultaneously some 11 000 IR data for each of the isotopomers including 153 mm wave data for 12CH₃35Cl. The assignments involve 12 sets of transitions (6 cold bands, 3 hot bands, and 3 pure rotational systems for ¹²CH₃³⁵Cl). The standard deviation was on average 0.00014 cm⁻¹ and 175 kHz for the IR and MMW data, respectively. The v₃=v₆=1 state was analysed for the first time principally from observed hot band transitions.