Electronic structure of N-sulfonylimines

The electronic structure of N-sulfonylimines has been studied in detail using ab initio MO and density functional methods. The S–N rotational barriers in HS(O)₂N=CH₂ at G2MP2 and CBS-Q levels have been found to be 3.25 and 3.43 kcal/mol respectively. Complete optimization at HF/6-31+G^*, MP2(full)/6-31+G^* and B3LYP/6-31+G^* levels have shown that synperiplanar arrangement of S–O with respect to C=N is more stable. NBO analysis has been carried out to quantitatively estimate these delocalisations and charge polarization in RS(O)₂N=CH₂ (R=H, Me, Cl, F). The Lewis basic character in N-sulfonylimines is less compared to N-alkylimines due to anomeric interactions that reduce the lone pair electron density on nitrogen in 1.     

The rotational spectrum of propynyl isocyanide

Propynyl isocyanide, CH₃C₂NC, has been prepared by vacuum pyrolysis of pentacarbonyl-(1,2-dichloropropenyl isocyanide) chromium, (CO)₅Cr–CN–C(Cl)=C(Cl)CH₃, and its ground state millimeter and microwave spectrum has been observed for the first time. r_s structural parameters of this molecule with a C_3v symmetry could be obtained from the rotational constants of several isotopomers: r_(C1–C2)=1.456(2) Å, r_(C2–C3)=1.206(2) Å, r_(C3–N)= 1.316(2) Å, r_(N–C4)= 1.175(2) Å, r_(H–C1)= 1.090(1) Å, >HCC=110.7(4)°. The nitrogen quadrupole coupling constant has been determined to be 878(2) kHz and measurements of the Stark effect allowed to obtain an electric dipole moment of 4.19(3) Debye. The results fit well into a series of related compounds and are in good agreement with data from ab initio calculations.     

Conformational stabilities of dimethylmethoxyphosphine and dimethyl(methylthio)phosphine from temperature dependent infrared spectra of rare gas solutions

Variable temperature (−55 to −150°C) studies of the infrared spectra (3500 to 400 cm⁻¹) of dimethylmethoxyphosphine, (CH₃)₂POCH₃ and dimethyl(methylthio)phosphine, (CH₃)₂PSCH₃ dissolved in liquid krypton and/or xenon have been recorded. From these data, the enthalpy differences have been determined to be 393±50 cm⁻¹ (4.71±0.60 kJ/mol), for (CH₃)₂POCH₃ with the near-cis conformer the more stable rotamer and 80±10cm⁻¹ (0.96±0.12 kJ/mol) for (CH₃)₂PSCH₃ with the cis conformer the more stable form. Complete vibrational assignments are presented for both molecules, which are consistent with the predicted frequencies obtained from the ab initio MP2/6-31G(d) calculations. The optimized geometries, conformational stabilities, harmonic force fields, infrared intensities, Raman activities, and depolarization ratios have been obtained from RHF/6-31G(d) and/or MP2/6-31G(d) ab initio calculations. These quantities are compared to the corresponding experimental quantities when appropriate as well as with some corresponding results for some similar molecules.     

Heavy atom structure and conformer stabilities of cyclopropyl carbinol from rotational spectroscopy and ab initio calculations

A remeasurement of the rotational spectra of the normal and hydroxyl deuterated isotopomers of cyclopropyl carbinol (cyclopropane methanol, (CH₂)₂CH(CH₂OH)) using Fourier-transform microwave spectroscopy has provided refined rotational constants and centrifugal distortion constants for this molecule. Rotational constants for an additional four singly substituted ¹³C isotopomers, the OD isotopomer, and the ¹⁸O isotopomer are consistent with a conformer in which the OH group forms an intramolecular hydrogen bond with the edge of the cyclopropyl ring. The observed a-type transition frequencies for the normal and deuterated species are in reasonable agreement with a previous microwave study (although some frequencies differ by several hundred kilohertz), but the few b- and c-type lines that were measured in the range of our spectrometer were found to differ by several megahertz from the previous literature measurements, leading to A rotational constants that differ significantly from those reported previously. The refined rotational constants for the normal isotopic species are A=12470.7795(23) MHz, B=3236.4678(7) MHz, C=2894.4831(7) MHz, while those of the deuterated species are A=12069.2653(24) MHz, B=3177.1540(8) MHz and C=2826.2658(7) MHz. Results of ab initio optimizations on seven conformers for this molecule carried out at the MP2/6-311+G(d,p) level will be compared with the experimentally determined structural parameters.     

Theoretical study of the elimination kinetics of several 2-substituted ethyl N,N-dimethylcarbamates in the gas phase, [(CH3)2NCOOCH2CH2Z, Z=CH2Cl, C≡CH, C≡N]

The theoretical studies of the gas-phase elimination of 2-substituted ethyl N,N-dimethylcarbamates (Z=CH₂Cl, C≡CH, C≡N) were performed using ab initio MP2/6-31G and MP2/6-31G(d) levels of theory. The gas phase elimination reaction of these carbamates yields N,N-dimethylcarbamic acid and the corresponding substituted olefin in a rate-determining step. The intermediate N,N-dimethylcarbamic acid is unstable and rapidly decomposes through a four-membered cyclic transition state to dimethylamine and CO₂ gas. The results of these calculations suggest a mechanism to be concerted, asynchronous, and a six-membered cyclic transition state structure. Plotting the relative theoretical rate coefficients against Taft's σ* values gave an approximate straight line (ρ*=0.4057, r=0.9894 at 360 °C). The correlation between experimental log k_rel vs. theoretical log k_rel. for these 2-substituted ethyl N,N-dimethylcarbamates gave an approximate straight line (r=0.9715 at 360 °C), suggesting the same type of mechanism.     

Structure and conformational properties of carbonylbisimidosulfuryl fluoride, O=C(N=S(O)F2)2

The molecular structure and conformational properties of O=C(N=S(O)F₂)₂ (carbonylbisimidosulfuryl fluoride) were determined by gas electron diffraction (GED) and quantumchemical calculations (HF/3-21G* and B3LYP/6-31G*). The analysis of the GED intensities resulted in a mixture of 76(12)% syn–syn and 24(12)% syn–anti conformer (ΔH⁰=H⁰(syn–anti)−H⁰(syn–syn)=1.11(32) kcal mol⁻¹) which is in agreement with the interpretation of the IR spectra (68(5)% syn–syn and 32(5)% syn–anti, ΔH⁰=0.87(11) kcal mol⁻¹). syn and anti describe the orientation of the S=N bonds relative to the C=O bond. In both conformers the S=O bonds of the two N=S(O)F₂ groups are trans to the C–N bonds. According to the theoretical calculations, structures with cis orientation of an S=O bond with respect to a C–N bond do not correspond to minima on the energy hyperface. The HF/3-21G* approximation predicts preference of the syn–anti structure (ΔE=−0.11 kcal mol⁻¹) and the B3LYP/6-31G* method results in an energy difference (ΔE=1.85 kcal mol⁻¹) which is slightly larger than the experimental values. The following geometric parameters for the O=C(N=S)₂ skeleton were derived (r_a values with 3σ uncertainties): C=O 1.193 (9) Å, C–N 1.365 (9) Å, S=N 1.466 (5) Å, O=C–N 125.1 (6)° and C–N=S 125.3 (10)°. The geometric parameters are reproduced satisfactorily by the HF/3-21G* approximation, except for the C–N=S angle which is too large by ca. 6°. The B3LYP method predicts all bonds to be too long by 0.02–0.05 Å and the C–N=S angle to be too small by ca. 4°.     

Anionic derivatives of pentafluoro-λ-sulfanyl (fluorosulfonyl) acetic acid esters

New ester salts [R₃NH]⁺[F₅SC(SO₂F)C(O)OR′]⁻ where RH, CH₃CH₂ and R′CH₃,(CH₃)₂CH have been prepared from corresponding esters and amines. The sodiumsalt Na[F₅SC(SO₂F)C(O)OCH(CH₃)₂] was used to prepare the following -substitutedderivatives: SF₅CX(SO₂F)C(O)OCH(CH₃)₂, XBr, Cl. The crystal structure of[(C₂H₅)₃NH]⁺[F₅SC(SO₂F)C(O)OCH₃]⁻ was determined and is monoclinic: P2₁/n;a=8.758(2) Å, b=9.645(2) Å and c=19.167(4) Å; β=97.92(3)°; V=1603.6 ų; Z=4.     

CO气氛下褐煤加压快速热解过程中CH_4的逸出规律

在管式反应器上进行了霍林河褐煤加压快速热解实验,研究了CO气氛下CH4逸出规律。在加压快速热解条件下,由于CO解离态吸附的O(a)吸附在煤上,提供了活性中心,电负性强的O(a)诱发其周围其他原子的电子云向O(a)偏移,减弱了原来化学键的强度,导致芳香环的开裂,侧链、醚键和脂肪链的断裂提供更多的自由基,稳定煤热解生成的碎片,促进了CH4的生成和逸出。因此,CO气氛下CH4产率较N2气氛下的高,在900℃、1.0 MPa时,50%CO气氛下的CH4产率较N2气氛下的提高了12.5%,并且CH4产率随着温度升高、压力的增大而增大。     

Conformational and structural studies of 1-chloropropane and 1-bromopropane from temperature-dependant FT-IR spectra of rare gas solutions and ab initio calculations

Variable temperature (−55 to −150°C) studies of the infrared spectra (3500–400 cm⁻¹) of 1-chloropropane (CH₃CH₂CH₂Cl) and 1-bromopropane (CH₃CH₂CH₂Br) dissolved in liquid krypton and xenon, respectively, have been recorded. Utilizing two conformer pairs in krypton solution for chloride and three conformer pairs in xenon solution for bromide, enthalpy differences of 52±3 cm⁻¹ (0.62±0.06 kJ/mol) and 72±7 cm⁻¹ (0.86±0.08 kJ/mol) were obtained for the chloride and bromide, respectively, with the gauche form being the more stable conformer for both molecules. From these data, it is estimated that 28 and 26% of trans form are present at ambient temperature for the chloride and bromide, respectively. The conformation stabilities, harmonic force constants, fundamental frequencies, infrared intensities and Raman activities have been obtained from RHF/6-31G(d) and/or MP2/6-31G(d) ab initio calculations for both halopropanes and these quantities have been compared to the experimental values when appropriate. The optimized geometries have also been obtained with several different ab initio basis sets with full electron correlation by the perturbation method up to MP2/6-311+G(2d,2p). The r₀ structural parameters of both halopropanes have been obtained by combining the ab initio data with the previously reported microwave rotational constants for both conformers. The quantities are compared to the corresponding results for some similar molecules.     

Electron diffraction study of the molecular structure and conformation of gaseous 2-furoyl chloride

The molecular structure of 2-furoyl chloride has been investigated by gas-phase electron diffraction at 86°C. Two distinct conformers were identified, a more stable planar form with the furan oxygen and the carbonyl oxygen syn and a less stable planar (or nearly planar) anti form. Assuming that the two forms differ in their geometries only in the O=C---C---O torsion angles and assuming the furan ring to have C_2v symmetry, the results for some of the distances (r_a) and angles (_a) are: r(C---H) = 1.110(20) Å, r(C=O) = 1.207(6) Å, r(C---O) = 1.378(10) Å, r(C??? = 1.465(13) A, (r(C---C)) (average carbon—carbon distance in the furan ring) = 1.392(8) A Δr(C---C) (difference between single and double carbon—carbon distances in the furan ring) = 0.069 A (assumed), r(C---Cl) = 1.787(6) A, C=C---COCl = 131.6(9)°, C=C---O = 110.9(4)°, C=C---H = 127.7(13.4)°, C---C=O = 125.8(8)° and C---C---Cl = 111.8(6)°. At 359 K the observed amount of the conformer with the oxygen atoms syn was 69.8(14.2)%.     

Synthesis and characterization of planarly chiral nonbridged bis(1-R-indenyl) zirconium dichloride complexes and X-ray structure of rac-[(η-C9H6-1-C(CH3)2---o-C6H4---OCH3)2ZrCl2]·THF

Reactions of the lithium salts of 3-substituted indenes 1, 2 with ZrCl₄(THF)₂ gave two series of nonbridged bis(1-substituted)indenyl zirconocene dichloride complexes. Fractional recrystallization from THF–petroleum ether furnished the pure racemic and mesomeric isomers of [(η⁵-C₉H₆-1-C(R¹)(R²)---o-C₆H₄---OCH₃)₂ZrCl₂]·nTHF (R¹=R²=CH₃, n=1, rac-1a and meso-1b; R¹=CH₃, R²=C₂H₅; n=0.5 or 0, rac-2a and meso-2b), respectively. Complex 1a was further characterized by X-ray diffraction to have a C₂ symmetrically racemic structure, where the six-member rings of the indenyl parts are oriented laterally and two o-CH₃O---C₆H₄---C(CH₃)₂--- substituents are oriented to the open side of the metallocene (Ind: bis-lateral, anti; Substituent: bis-central, syn). The four zirconocene complexes are highly symmetrical in solution as characterized by room temperature ¹H-NMR, however ¹H–¹H NOESY of meso-1b shows that some of the NOE interactions arise from the two separated indenyl parts of the same molecule, which can only be well explained by taking into account the torsion isomers in solution.     

Ab initio computation of the potential energy surfaces of the water·hydrocarbon complexes H2O·C2H2, H2O·C2H4 and H2O·CH4: minimum energy structures, vibrational frequencies and hydrogen bond energies

On the basis of ab initio MP2/6–31 + + G(2d,2p) calculations, we examined the potential energy surfaces of the water·hydrocarbon complexes H₂O·CH₄, H₂O·C₂H₂ and H₂O·C₂H₂ to locate all the minimum energy structures and estimate the hydrogen bond energies and vibrational frequencies associated with the C(spⁿ)---H·O and the O---H·C(spⁿ) bonds (n = 1−3). Our calculations show that H₂O·C₂H₂, H₂O·C₂H₄ and H₂O·CH₄ have two minimum energy structures (i.e., the C---H·O and O---H·C hydrogen bond forms), but H₂O·C₂H₄ has only one when the vibrational motion is taken into account, the O---H·C hydrogen bond form. We have also computed the barrier for the interconversion from one minimum to the other. The fully optimized geometries of H₂O·CH₄, H₂O·C₂H₄ and H₂O·C₂H₂ as well as the vibrational shifts of the C---H stretching frequencies in their C---H·O hydrogen-bonded forms are in good agreement with the available experimental data. The calculated hydrogen bond energies show that the C(spⁿ---H·O bond strengths decrease in the order C(sp)---H·O>C(sp²)---H·O>C(sp³)---O>C(sp³---H·O, which is also consistent with the available experimental data.     

New heterometallic copper zinc alkoxides: synthesis, structure properties and pyrolysis to Cu/ZnO composites

The copper compound [(THF)KCu(O^tBu)₃]_∞ 1 was obtained by interaction of a 1:1 mixture of ZnCl₂/CuCl₂ with KO^tBu. Bi- and trifunctional aminoalcohols were used to synthesize the intramolecularly donor stabilized Cu(II) alkoxides Cu(OCH(R)CH₂NMe₂)₂ (3: R=Me, 4: =CH₂NMe₂) where 4 was structurally characterized. Lewis acid–base adduct formation with (Me₃Si)₃CZnCl gave the heterodinuclear compounds (Me₃Si)₃CZnCl · Cu(OCH(R)CH₂NMe₂)₂ (5: R=Me, 6: R=CH₂NMe₂), which were characterized by X-ray single-crystal structure analysis. The two metal centers Cu and Zn of 5 and 6 are bridged by two oxygen atoms to form a Cu–O–Zn core. Pyrolysis of compounds 5 and 6 in dry argon or a H₂/N₂ mixture at atmospheric pressure forms metallic copper and zinc oxide, whereas pyrolysis under O₂/Ar forms additionally oxidized copper species. Elemental analysis of the pyrolysis products showed carbon and nitrogen contamination. Scanning electron microscopy and energy dispersive X-ray analysis were performed to get information on the morphology and the chemical composition of the pyrolysis products.     

Structure and conformation of cyclobutylsilane: an electron diffraction and ab initio study

A gas electron diffraction study of cyclobutylsilane results in a mixture of equatorial and axial conformers, with the equatorial confomer slightly more stable (Δ G = 0.8 ± 0.4 kJ mol⁻¹). The cyclobutyl ring is distorted with the adjacent bonds longer (C₁---C₂ = 1.573 (4) Å) than the opposite bonds (C₂---C₃ = 1.557 (4) Å). The experimental values for the energy difference between the two conformers and for the geometric parameters are reproduced very well by ab initio calculations. The importance of silicon 3d orbitals in the interpretation of ring distortion is ambiguous, but on the basis of the ab initio calculations the participation of silicon 3d functions is negligible.     

EPR/ENDOR study of an X-irradiated single crystal of: 1-triphenylphosphoranylidene-2-propanone: The role of hydrogen bonds in the trapping of radiogenic radicals

As shown from the crystal structure, the oxygen atom of Ph₃P=CH---C(O)CH₃ forms both intra and intermolecular hydrogen bonds. X-irradiation of this compounds produces a room-temperature-stable radical which was studied by single crystal EPR/ENDOR spectroscopy. Comparison of the experimental hyperfine couplings with those obtained from ab initio calculations shows that the radical cation Ph₃P⁺---CH=C(OH)CH₂ is formed under radiolysis. The principal directions of the hyperfine tensors indicate that, in this process, some of the hydrogen bonds are broken and that the radical undergoes a drastic reorientation around the Ph₃P---C bond.     

Infrared and Raman spectra, conformational stability, ab initio calculations of structure, and vibrational assignment of 2-hexyne

The infrared spectra (3500–50 cm⁻¹) of the gas and solid and the Raman spectra (3500–50 cm⁻¹) of the liquid and solid have been recorded for 2-hexyne, CH₃–CC–CH₂CH₂CH₃. Variable temperature studies of the infrared spectrum (3500–400 cm⁻¹) of 2-hexyne dissolved in liquid krypton have also been recorded. Utilizing four anti/gauche conformer pairs, the anti(trans) conformer is found to be the lower energy form with an enthalpy difference of 74±8 cm⁻¹ (0.88±0.10 kJ/mol) determined from krypton solutions over the temperature range −105 to −150 °C. At room temperature it is estimated that there is 42% of the anti conformer present. Equilibrium geometries and energies of the two conformers have been determined by ab initio (HF and MP2) and hybrid DFT (B3LYP) methods using a number of basis sets. Only the HF and DFT methods predict the anti conformer as the more stable form as found experimentally. A vibrational assignment is proposed based on the force constants, relative intensities, depolarization ratios from the ab initio and DFT calculations and on rotational band contours obtained using the calculated equilibrium geometries. From calculated energies it is shown that the CH₃ group exhibits almost completely free rotation which is in agreement with the observation of sub-band structure for the degenerate methyl vibrations from which values of the Coriolis coupling constants, ζ, have been determined. The results are compared to similar properties of some corresponding molecules.     

Synthesis and characterisation of four- and eight-membered ring auralactam complexes

The reactions of the cyclo-aurated gold(III) dihalide complex [{C₆H₃(CH₂NMe₂)-2-(OMe)-5}AuCl₂] with N-cyanoacetylurethane [NCCH₂C(O)NHCO₂Et], 2-benzoylacetanilide [PhC(O)CH₂C(O)NHPh] and acetoacetanilide [MeC(O)CH₂C(O)NHPh], and [{C₆H₄(CH₂NMe₂)-2}AuCl₂] with acetoacetanilide in dichloromethane with excess silver(I) oxide gives the first examples of auralactam complexes, containing (O)---CHR′ four-membered rings. A single-crystal X-ray diffraction study on the complex [{C₆H₄(CH₂NMe₂)-2}A H(COMe)}] reveals similar structural features to related metallalactam complexes of platinum(II) and palladium(II). When a CDCl₃ solution of the complex [{C₆H₃(CH₂NMe₂)-2-(OMe)-5}A HCN}] is allowed to stand for 18 h, a novel dimerisation reaction occurs, giving the insoluble product [{C₆H₃(CH₂NMe₂)-2-(OMe)-5}Au{N(CO₂Et)C(O)CHCN}]₂·2CDCl₃, characterised by an X-ray structure determination. The dimer contains an eight-membered A

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ring.     

Microwave-assisted pyrolysis of CH4/N2 mixtures over activated carbon

The aim of this work was to study the microwave-assisted pyrolysis of CH₄ over an activated carbon, which acted as both microwave receptor and catalyst, and the influence of using different CH₄/N₂ ratios on the conversion of CH₄ to H₂. In order to compare the results obtained in the microwave oven, the pyrolysis was also carried out under conventional heating (electric furnace, EF). The effects of N₂, which enhanced significantly CH₄ conversion, differed depending on the heating device used. Under EF heating, N₂ seemed to have an effect similar to distribute the CH₄ molecules within the activated carbon bed. Under microwave heating (MW), the N₂, as well as distributing the CH₄ molecules, favoured the generation of energetic microplasmas, leading to higher conversions. The prevalence of one role over the other depended on the CH₄/N₂ ratio, the appearance of energetic microplasmas being favoured with high percentages of N₂. Consequently, CH₄ conversion was higher at low CH₄/N₂ ratios. Additionally, the formation of carbon nanofibres in experiments where a combination of N₂ and MW heating was used is also reported.     

Molecular structure and conformational stability of allylisocyanate—post-Hartree–Fock and density functional theory studies

The molecular structure and conformational stability of allylisocyanate (CH₂CHCH₂NCO) molecule was studied using the ab initio and DFT methods. The geometries of possible conformers, C-gauche (δ=120°, θ=0°) (δ=C=C–C–N and θ=C–C–N=C) and C-cis N-trans (δ=0° and θ=180°) were optimized employing HF/6-31G^*, MP2/6-31G^* levels of theory of ab initio and BLYP, B3LYP, BPW91 and B3PW91 methods of DFT implementing the atomic basis set 6-311+G(d,p). The structural and physical parameters of the above conformers were discussed with the experimental and theoretical values of the related molecules, methylisocyanate and 3-fluoropropene. It has been found that the N=C=O bond angle is not linear as the experimental result for both the conformers and the theoretical bond angle is 173°. The rotational potential energy surfaces have been performed at the HF/6-31G^*, and MP2/6-31G^* levels of theory. The Fourier decomposition potentials were analysed at the HF/6-31G^*, and MP2/6-31G^* levels of theory. The HF/6-31G^* level of theory predicted that the C-gauche conformer is more stable than the C-cis N-trans conformer by 0.41 kJ/mol, but the MP2 and DFT methods predicted the C-cis N-trans conformer is found to be more stable than the C-gauche conformer. The calculated chemical hardness value at the HF/6-31G^* level of theory predicted the C-cis N-trans form is more stable than C-gauche form, whereas the chemical hardness value at the MP2/6-31G^* level of theory favours the slight preference towards the C-gauge conformer.     

A comparative ab initio study of methyl formate, methyl thiolformate and methyl thionoformate

Ab initio SCF-MO calculations have been carried out for HCOOCH₃, HC(=O)SCH₃ and HC(=S)OCH₃. Relative stabilities of s-trans/s-cis conformers are reported and discussed in terms of specific intramolecular interactions. The energy difference between the s-trans and the s-cis form increases in the order methyl thiolformate < methyl thionoformate < methyl formate. The major stabilizing factors of the s-cis forms are the bond dipolar interaction and the mesomeric delocalization through the five member ring involving both the X=C---Y---C (X, Y = O, S) skeleton and the out-of-plane hydrogen atoms. These effects are used to explain the trends mentioned. The non-planarity previously proposed for the thionoester is reinvestigated. Our calculations show that this molecule is planar. Molecular atomic charges, dipole moments and ionisation potentials are determined and compared with available experimental values.