Structure, stability, and spectra of C9H3, C11H3, and C13H3 radicals

Density functional theory has been used to investigate the geometries, vibrational frequencies, rotational constants, and dipole moments of the C(9)H(3), C(11)H(3), and C(13)H(3) radicals. Vertical electronic transition energies of C(9)H(3), C(11)H(3), and C(13)H(3) are calculated by the time-dependent density functional theory. Present results show that the most stable arrangements of C(9)H(3), C(11)H(3), and C(13)H(3) are H(2)C(9)H, H(2)C(11)H, and H(2)C(13)H with a C(2v) symmetry, respectively. Such lowest-energy isomers have an obvious single and triple bond alternation carbon chain. Their isomers HC(4)(HC)C(4)H, HC(4)[C(C(2)H)]C(4)H, and C(C(4)H)(3) are predicted to have vibrational frequencies and vertical excitation energies in good agreement with experimental observations. HC(4)(HC)C(4)H, HC(4)[C(C(2)H)]C(4)H, and C(C(4)H)(3) have similar trigonal structure, which gives rise to the remarkably similar spectroscopic features as obtained experimentally. On the basis of present calculations, the isomers HC(4)(HC)C(4)H, HC(4)[C(C(2)H)]C(4)H, and C(C(4)H)(3) of C(9)H(3), C(11)H(3), and C(13)H(3) radicals are most likely the carriers of the observed spectra.     

On the viability of small endohedral hydrocarbon cage complexes: X@C4H4, X@C8H8, X@C8H14, X@C10H16, X@C12H12, AND X@C16H16

Small hydrocarbon complexes (X@cage) incorporating cage-centered endohedral atoms and ions (X = H(+), H, He, Ne, Ar, Li(0,+), Be(0,+,2+), Na(0,+), Mg(0,+,2+)) have been studied at the B3LYP/6-31G(d) hybrid HF/DFT level of theory. No tetrahedrane (C(4)H(4), T(d)()) endohedral complexes are minima, not even with the very small hydrogen atom or beryllium dication. Cubane (C(8)H(8), O(h)()) and bicyclo[2.2.2]octane (C(8)H(14), D(3)(h)()) minima are limited to encapsulating species smaller than Ne and Na(+). Despite its intermediate size, adamantane (C(10)H(16), T(d)()) can enclose a wide variety of endohedral atoms and ions including H, He, Ne, Li(0,+), Be(0,+,2+), Na(0,+), and Mg(2+). In contrast, the truncated tetrahedrane (C(12)H(12), T(d)()) encapsulates fewer species, while the D(4)(d)() symmetric C(16)H(16) hydrocarbon cage (see Table of Contents graphic) encapsulates all but the larger Be, Mg, and Mg(+) species. The host cages have more compact geometries when metal atoms, rather than cations, are inside. This is due to electron donation from the endohedral metals into C-C bonding and C-H antibonding cage molecular orbitals. The relative stabilities of endohedral minima are evaluated by comparing their energies (E(endo)) to the sum of their isolated components (E(inc) = E(endo) - E(cage) - E(x)) and to their exohedral isomer energies (E(isom) = E(endo) - E(exo)). Although exohedral binding is preferred to endohedral encapsulation without exception (i.e., E(isom) is always exothermic), Be(2+)@C(10)H(16) (T(d)(); -235.5 kcal/mol), Li(+)@C(12)H(12) (T(d)(); 50.2 kcal/mol), Be(2+)@C(12)H(12) (T(d)(); -181.2 kcal/mol), Mg(2+)@C(12)H(12) (T(d)(); -45.0 kcal/mol), Li(+)@C(16)H(16) (D(4)(d)(); 13.3 kcal/mol), Be(+)@C(16)H(16) (C(4)(v)(); 31.8 kcal/mol), Be(2+)@C(16)H(16) (D(4)(d)(); -239.2 kcal/mol), and Mg(2+)@C(16)H(16) (D(4)(d)(); -37.7 kcal/mol) are relatively stable as compared to experimentally known He@C(20)H(20) (I(h)()), which has an E(inc) = 37.9 kcal/mol and E(isom) = -35.4 kcal/mol. Overall, endohedral cage complexes with low parent cage strain energies, large cage internal cavity volumes, and a small, highly charged guest species are the most viable synthetic targets.     

Rotational spectrum and carbon-13 hyperfine structure of the C3H, C5H, C6H, and C7H radicals

By means of Fourier transform microwave spectroscopy of a supersonic molecular beam, we have detected the singly substituted carbon-13 isotopic species of C(5)H, C(6)H, and C(7)H. Hyperfine structure in the rotational transitions of the lowest-energy fine structure component ((2)Pi(12) for C(5)H and C(7)H, and (2)Pi(32) for C(6)H) of each species was measured between 6 and 22 GHz, and precise rotational, centrifugal distortion, Lambda-doubling, and (13)C hyperfine coupling constants were determined. In addition, resolved hyperfine structure in the lowest rotational transition (J = 32-->12) of the three (13)C isotopic species of C(3)H was measured by the same technique. By combining the centimeter-wave measurements here with previous millimeter-wave data, a complete set of (13)C hyperfine coupling constants were derived to high precision for each isotopic species. Experimental structures (r(0)) have been determined for C(5)H and the two longer carbon-chain radicals, and these are found to be in good agreement with the predictions of high-level coupled-cluster calculations. C(3)H, C(5)H, and C(7)H exhibit a clear alternation in the magnitude and sign of the (13)C hyperfine coupling constants along the carbon-chain backbone. Because the electron spin density is nominally zero at the central carbon atom of C(3)H, C(5)H, and C(7)H, and at alternating sets of carbon atoms of C(5)H and C(7)H, owing to spin polarization, almost all of the (13)C coupling constants at these atoms are small in magnitude and negative in sign. Spin-polarization effects are known to be important for the Fermi-contact (b(F)) term, but prior to the work here they have generally been neglected for the hyperfine terms a, c, and d.     

H atom yields from the reactions of CN radicals with C2H2, C2H4, C3H6, trans-2-C4H8, and iso-C4H8

The kinetics and H atom channel yield at both 298 and 195 K have been determined for reactions of CN radicals with C2H2 (1.00+/-0.21, 0.97+/-0.20), C2H4 (0.96+/-0.032, 1.04+/-0.042), C3H6 (pressure dependent), iso-C4H8 (pressure dependent), and trans-2-C4H8 (0.039+/-0.019, 0.029+/-0.047) where the first figure in each bracket is the H atom yield at 298 K and the second is that at 195 K. The kinetics of all reactions were studied by monitoring both CN decay and H atom growth by laser-induced fluorescence at 357.7 and 121.6 nm, respectively. The results are in good agreement with previous studies where available. The rate coefficients for the reaction of CN with trans-2-butene and iso-butene have been measured at 298 and 195 K for the first time, and the rate coefficients are as follows: k298K=(2.93+/-0.23)x10(-10) cm3 molecule(-1) s(-1), k195K=(3.58+/-0.43)x10(-10) cm3 molecule(-1) s(-1) and k298K=(3.17+/-0.10)x10(-10) cm3 molecule(-1) s(-1), k195K=(4.32+/-0.35)x10(-10) cm3 molecule(-1) s(-1), respectively, where the errors represent a combination of statistical uncertainty (2sigma) and an estimate of possible systematic errors. A potential energy surface for the CN+C3H6 reaction has been constructed using G3X//UB3LYP electronic structure calculations identifying a number of reaction channels leading to either H, CH3, or HCN elimination following the formation of initial addition complexes. Results from the potential energy surface calculations have been used to run master equation calculations with the ratio of primary:secondary addition, the average amount of downward energy transferred in a collision DeltaEd, and the difference in barrier heights between H atom elimination and an H atom 1, 2 migration as variable parameters. Excellent agreement is obtained with the experimental 298 K H atom yields with the following parameter values: secondary addition complex formation equal to 80%, DeltaEd=145 cm(-1), and the barrier height for H atom elimination set 5 kJ mol(-1) lower than the barrier for migration. Finally, very low temperature master equation simulations using the best fit parameters have been carried out in an increased precision environment utilizing quad-double and double-double arithmetic to predict H and CH3 yields for the CN+C3H6 reaction at temperatures and pressures relevant to Titan. The H and CH3 yields predicted by the master equation have been parametrized in a simple equation for use in modeling.     

αH,αH,ωH-全氟烷氧丙基甲基二氯硅烷的制备和水解反应研究

<正>我们以十六烷基三甲基澳化按为相转移催化剂,将四氟乙烯调聚醇与氛丙烯在氢氧化钠存在下反应,制得三种     

Heat-Induced Reactions of 6-Bromo-, 6-Chloro-, and 6-(Methylsulfanyl)octafl uoroindane-5-thiols with Tetrafluoroethylene. Synthesis of Dodecafluoro-2 H ,3 H ,5 H ,6 H ,7 H -indeno[5,6- b ]thiophene

Dodecafluoro-2H,3H,5H,6H,7H-indeno[5,6-b]thiophene has been synthesized as the major product of co-pyrolysis of 6-bromo-, 6-chlorooctafluoroindane-5-thiols, or bis(6-bromo-5-perfluoroindanyl)disulfane with tetrafluoroethylene under flow conditions at 400-625ºC, along with small amount of tetradecafluoro-1,2,3,5,6,7-hexahydro-s-indacene. Dodecafluoro-2H,3H,5H,6H,7H-indeno[5,6-b]thiophene formed in the reaction of 6-(meth-ylsulfanyl)octafluoroindane-5-thiol with tetrafluoroethylene at 420ºC has been isolated, and its structure has been confirmed by X-ray diffraction analysis. The schemes of the products formation involving intermediate radicals have been proposed.     

Structure of cucumariosides H5, H6, H7 and H8, triterpene glycosides from the sea cucumber Eupentacta fraudatrix and unprecedented aglycone with 16,22-epoxy-group

Four new triterpene glycosides cucumariosides H5 (1), H6 (2), H7 (3) and H8 (4) along with the known cucumarioside H (5) have been isolated from the Far Eastern sea cucumber Eupentacta fraudatrix. The structures of glycosides 1-4 were elucidated on the basis of spectral data (2D NMR and MS). Glycosides 1-4 belong to the group o f cucumariosides H having branched rare pentasaccharidecarbohydrate moieties with one sulfate group and 3-O-methyl-D-xylose as a terminal monosaccharide unit. Glycosides 1-3 and 5 differ from each other in structures of side chains of the aglycones, while cucumarioside H8 (4) has a novel aglycone with unprecedented 16(22)-epoxy-group, never found in the sea cucumbers glycosides. Glycosides 1-3, and 5 were cytotoxic against mouse lymphocytes and hemolytic against mouse erythrocytes. Glycoside 2 was less active in comparison with others.     

Synthesis of two new families of fluorinated compounds: 1H,1H,2H,2H-perfluoro-3,5-alkyldiynols and 1H,1H-perfluoro-2,4-alkyldiynols and their acrylates and methacrylates

The synthesis of two new families of compounds, 1H,1H,2H,2H-perfluoro-3,5-alkyldiynols and 1H,1H-perfluoro-2,4-alkyldiynols, and their acrylates and methacrylates, precursors of polymeric systems with important physical properties, is described.     

Eremophilane esters of Robinsonecio gerberifolius and their rearranged products. Study of the coupling constants (2)J(H, H), (3)J(H, H) and (4)J(H, H)

In the course of the basic hydrolysis of four eremophilane esters isolated from Robinsonecio gerberifolius, some rearrangements, eliminations, and additions occurred. Five compounds were obtained, three of them not previously described. Additionally, a new sesquiterpene was produced by autooxidation of compound 1. The (1)H and (13)C NMR spectra of these compounds were completely assigned by utilization of HMQC, HMBC, COSY, DEPT, and NOESY techniques. The long-range coupling constants of the peroxide 10 are reported, and all its coupling constants (2)J(H, H), (3)J(H, H), and (4)J(H, H) are calculated at the B3LYP/6-31G(d,p) level of theory. Their magnitude is explained in terms of electronic delocalization and the additivity of stereoelectronic effects.     

Accurate ab initio predictions of ionization energies of hydrocarbon radicals: CH2, CH3, C2H, C2H3, C2H5, C3H3, and C3H5

The ionization energies for methylene (CH2), methyl (CH3), ethynyl (C2H), vinyl (C2H3), ethyl (C2H5), propargyl (C3H3), and allyl (C3H5) radicals have been calculated by the wave-function-based ab initio CCSD(T)/CBS approach, which involves the approximation to the complete basis set (CBS) limit at the coupled-cluster level with single and double excitations plus a quasiperturbative triple excitation [CCSD(T)]. When it is appropriate, the zero-point vibrational energy correction, the core-valence electronic correction, the scalar relativistic effect correction, the diagonal Born-Oppenheimer correction, and the high-order correlation correction have also been made in these calculations. The comparison between the computed ionization energy (IE) values and the highly precise experimental IE values determined in previous pulsed field ionization-photoelectron (PFI-PE) studies indicates that the CCSD(T)/CBS method is capable of providing accurate IE predictions for these hydrocarbon radicals achieving error limits well within +/-10 meV. The benchmarking of the CCSD(T)/CBS IE predictions by the PFI-PE experimental results also lends strong support for the conclusion that the CCSD(T)/CBS approach with high-level energy corrections can serve as a valuable alternative for reliable IE determination of radicals, particularly for those radicals with very unfavorable Franck-Condon factors for photoionization transitions near their ionization thresholds.     

Theoretical study of isoelectronic molecules: B6H10, 2-CB5H9, 2,3-C2B4H8, 2,3,4-C3B3H7, and 2,3,4,5-C4B2H6

Isoelectronic molecules regarding B6H10, 2-CB5H9, 2,3-C2B4H8, 2,3,4-C3B3H7, and 2,3,4,5-C4B2H6 are studied by the density functional B3LYP/6-311G(d,p) method and the electron propagator theory in the partial third-order quasiparticale approximation, as well as the extrapolated calculation with the coupled-cluster CCSD(T) theory. The calculated ionization potentials are in good agreement with the experimental data from photoelectron spectroscopy. Valence structures are characterized with natural orbital bond (NBO) theory, exhibiting the multiple three-center two-electron bonds B-H-B, B-B-B, C-B-B, B-C-B, and C-B-C, and chemical bond rearrangements in the cations.     

紫外光固化聚多氟烷氧丙基甲基硅氧烷的研究

本文报道几种紫外光敏有机硅单体:(γ-甲基丙烯酰氧)丙基甲基二甲氧基硅烷,1,3,5,7-四(γ-甲基丙烯酰氧丙基)四甲基环四硅氧烷和1,3-双(甲基丙烯酰氧甲基)-1,1,3,3-四甲基二硅氧烷的合成,以及它们与αH,αH,ωH-全氟烷氧丙基甲基环四硅氧烷的开环共聚反应,制备了一系列新型光敏聚多氟烷氧丙基甲基硅氧烷.并初步研究了在紫外光辐照下,这类光敏聚多氟烷氧丙基甲基硅氧烷的化学结构对固化速度的影响.     

Mapping Post-translational Modifications of Histones H2A, H2B and H4 in Schizosaccharomyces pombe

Core histones are known to carry a variety of post-translational modifications (PTMs), including acetylation, phosphorylation, methylation and ubiquitination, which play important roles in the epigenetic control of gene expression. The nature and biological functions of these PTMs in histones from plants, animals and budding yeast have been extensively investigated. In contrast, the corresponding studies for fission yeast were mainly focused on histone H3. In the present study, we applied LC-nano-ESI-MS/MS, coupled with multiple protease digestion, to identify PTMs in histones H2A, H2B and H4 from Schizosaccharomyces pombe (S. pombe), the typical model organism of fission yeast. Various protease digestions provided high sequence coverage for PTM mapping, and accurate mass measurement of fragment ions allowed for unambiguous differentiation of acetylation from tri-methylation. Many modification sites conserved in other organisms were identified in S. pombe. In addition, some unique modification sites, including N-terminal acetylation in H2A and H2B as well as K123 acetylation in H2A.β, were observed. Our results provide a comprehensive picture of the PTMs of histones H2A, H2B and H4 in S. pombe, which serves as a foundation for future investigations on the regulation and functions of histone modifications in this important model organism.     

Quasiclassical trajectory calculations of the reaction C+C2H2-->l-C3H, c-C3H+H, C3+H2 using full-dimensional triplet and singlet potential energy surfaces

Full-dimensional, density functional theory (B3LYP/6-311g(d,p))-based potential energy surfaces (PESs) are reported and used in quasi-classical calculations of the reaction of C with C(2)H(2). For the triplet case, the PES spans the region of the reactants, the complex region (with numerous minima and saddle points) and the products, linear(l)-C(3)H+H, cyclic(c)-C(3)H+H and c-(3)C(3)+H(2). For the singlet case, the PES describes the complex region and products l-C(3)H+H, c-C(3)H+H and l-(1)C(3)+H(2). The PESs are invariant under permutation of like nuclei and are fit to tens of thousands of electronic energies. Energies and harmonic frequencies of the PESs agree well the DFT ones for all stationary points and for the reactant and the products. Dynamics calculations on the triplet PES find both l-C(3)H and c-C(3)H products, with l-C(3)H being dominant at the energies considered. Limited unimolecular reaction dynamics on the singlet PES find both products in comparable amounts as well as the C(3)+H(2) product.     

Association rate constants for reactions between resonance-stabilized radicals: C3H3 + C3H3, C3H3 + C3H5, and C3H5 + C3H5

Reactions between resonance-stabilized radicals play an important role in combustion chemistry. The theoretical prediction of rate coefficients and product distributions for such reactions is complicated by the fact that the initial complex-formation steps and some dissociation steps are barrierless. In this paper direct variable reaction coordinate transition state theory (VRC-TST) is used to predict accurately the association rate constants for the self and cross reactions of propargyl and allyl radicals. For each reaction, a set of multifaceted dividing surfaces is used to account for the multiple possible addition channels. Because of their resonant nature the geometric relaxation of the radicals is important. Here, the effect of this relaxation is explicitly calculated with the UB3LYP/cc-pvdz method for each mutual orientation encountered in the configurational integrals over the transition state dividing surfaces. The final energies are obtained from CASPT2/cc-pvdz calculations with all pi-orbitals in the active space. Evaluations along the minimum energy path suggest that basis set corrections are negligible. The VRC-TST approach was also used to calculate the association rate constant and the corresponding number of states for the C(6)H(5) + H --> C(6)H(6) exit channel of the C(3)H(3) + C(3)H(3) reaction, which is also barrierless. For this reaction, the interaction energies were evaluated with the CASPT2(2e,2o)/cc-pvdz method and a 1-D correction is included on the basis of CAS+1+2+QC/aug-cc-pvtz calculations for the CH(3) + H reference system. For the C(3)H(3) + C(3)H(3) reaction, the VRC-TST results for the energy and angular momentum resolved numbers of states in the entrance channels and in the C(6)H(5) + H exit channel are incorporated in a master equation simulation to determine the temperature and pressure dependence of the phenomenological rate coefficients. The rate constants for the C(3)H(3) + C(3)H(3) and C(3)H(5) + C(3)H(5) self-reactions compare favorably with the available experimental data. To our knowledge there are no experimental rate data for the C(3)H(3) + C(3)H(5) reaction.     

An efficient one-pot, three-component synthesis of indeno[1,2-b]quinoline-9,11(6H,10H)-dione, acridine-1,8(2H,5H)-dione and quinoline-3-carbonitrile derivatives from enaminones

An efficient one-pot, three-component method for the preparation of indeno[1,2-b]quinoline-9,11(6H,10H)-dione, acridine-1,8(2H,5H)-dione and various multi-substituted quinoline-3-carbonitrile derivatives has been developed through the Michael addition to enaminones, which was achieved by both microwave irradiation and conventional heating.     

Assignment and sign determination of (C,H) and (H,H) coupling constants in N-acetylimidazole with selective population inversion experiments

The assignment of the (C, H) couplings in N-acetylimidazole and the determination of the relative signs of all (C, H) and (H, H) couplings with SPI experiments are described. All coupling constants are of the same, positive, sign as the directly-bonded (C, H) coupling constants. Some advantageous features of the SPI technique, such as selectivity and increased sensitivity, are discussed in comparison to conventional double irradiation methods.     

Theoretical study on the substitution reactions of silylenoid H2SiLiF with CH4, NH3, H2O, HF, SiH4, PH3, H2S, and HCl

DFT calculations at the B3LYP/6-31G(d,p) level have been performed to explore the substitution reactions of silylenoid H(2)SiLiF with XH(n) hydrides, where XH(n) = CH(4), NH(3), H(2)O, HF, SiH(4), PH(3), H(2)S, and HCl. We have identified a previously unreported reaction pathway on each reaction surface, H(2)SiLiF + XH(n) --> H(3)SiF + LiXH(n-1), which involved the initial formation of an association complex via a five-membered cyclic transition state to form an intermediate followed by the substituted product H(3)SiF with LiXH(n-1) dissociating. These theoretical calculations suggest that (i) there is a very clear trend toward lower activation barriers and more exothermic interactions on going from left to right along a given row in the periodic table, and (ii) for the second-row hydrides, the substitution reactions are more exothermic than for the first-row hydrides and the reaction barriers are lower. The solvent effects were considered by means of the polarized continuum model (PCM) using THF as a solvent. The presence of THF solvent disfavors slightly the substitution reaction. Compared to the previously reported insertions and H(2)-elimination reactions of H(2)SiLiF and XH(n), the substitution reactions should be most favorable.     

Adsorption of O, H, OH, and H2O on Ag(100)

The adsorption of H(2)O and its dissociation products, O, H, and OH, on Ag(100) has been studied using an ab initio embedding method. Results at different sites (atop, bridge, and hollow) are presented. The four-fold hollow site is found to be the most stable adsorption site for O, H, and OH, and the calculated adsorption energies are 87.1, 42.7, and 76.2 kcal mol(-1), respectively. The adsorption energy of water at the atop and bridge sites is almost identical with values of 11.1 and 12.0 kcal mol(-1), respectively. The formation of adsorbed OH species by adsorption of water on oxygen-precovered Ag(100) is predicted to be exothermic by 36 kcal mol(-1).     

Chemically activated reactions on the C7H5 energy surface: propargyl + diacetylene, i-C5H3 + acetylene, and n-C5H3 + acetylene

This study uses computational chemistry and statistical reaction rate theory to investigate the chemically activated reaction of diacetylene (butadiyne, C(4)H(2)) with the propargyl radical (C˙H(2)CCH) and the reaction of acetylene (C(2)H(2)) with the i-C(5)H(3) (CH(2)CCCC˙H) and n-C(5)H(3) (CHCC˙HCCH) radicals. A detailed G3SX-level C(7)H(5) energy surface demonstrates that the C(3)H(3) + C(4)H(2) and C(5)H(3) + C(2)H(2) addition reactions proceed with moderate barriers, on the order of 10 to 15 kcal mol(-1), and form activated open-chain C(7)H(5) species that can isomerize to the fulvenallenyl radical with the highest barrier still significantly below the entrance channel energy. Higher-energy pathways are available leading to other C(7)H(5) isomers and to a number of C(7)H(4) species + H. Rate constants in the large multiple-well (15) multiple-channel (30) chemically activated system are obtained from a stochastic solution of the one-dimensional master equation, with RRKM theory for microcanonical rate constants. The dominant products of the C(4)H(2) + C(3)H(3) reaction at combustion-relevant temperatures and pressures are i-C(5)H(3) + C(2)H(2) and CH(2)CCHCCCCH + H, along with several quenched C(7)H(5) intermediate species below 1500 K. The major products in the n-C(5)H(3) + C(2)H(2) reaction are i-C(5)H(3) + C(2)H(2) and a number of C(7)H(4) species + H, with C(7)H(5) radical stabilization at lower temperatures. The i-C(5)H(3) + C(2)H(2) reaction predominantly leads to C(7)H(4) + H and to stabilized C(7)H(5) products. The title reactions may play an important role in polycyclic aromatic hydrocarbon (PAH) formation in combustion systems. The C(7)H(5) potential energy surface developed here also provides insight into several other important reacting gas-phase systems relevant to combustion and astrochemistry, including C(2)H + the C(3)H(4) isomers propyne and allene, benzyne + CH, benzene + C((3)P), and C(7)H(5) radical decomposition, for which some preliminary analysis is presented.