Acephenanthrylenes from flash vacuum thermolysis of diarylmethylidenecycloproparenes

Upon flash vacuum thermolysis at 750 °C fluorenylidenecyclopropa[b]naphthalene (1) undergoes opening of the three-membered ring and rearrangement to give a range of C₂₄H₁₄ polycyclic aromatic hydrocarbons. Dibenz[e.l]- and -[e.k]acephenanthrylene (7) and (12), respectively, have been identified while the plausible naphth[1,2-e]- and [2,3-e]acephenanthrylenes (9) and (14) were not detected. With diphenylmethylidenecyclopropa[b]naphthalene (2) cyclodehydrogenation and rearrangement also provide C₂₄H₁₄ polycycles; dibenz[e.k]acephenanthrylene (12) is identified and dibenz[a.e]aceanthrylene (15) is a proposed product.     

On a novel coordination mode of phosphinine C5H5P

In an unprecedented coordination mode two phosphinines simultaneously bridge a Mn-Mn bond and the latter with two Mn(CO)3 fragments; the distortion of the resulting central heterobicyclo[1.1.0]butane unit follows from the Mn(18VE) requirement.     

A theoretical study of the formation of phosphaacetylene by thermolysis of triallylphosphine

A theoretical study of the decomposition of triallylphosphine into phosphaacetylene at the B3LYP/6-311++G(3df,2p) level has shown that the most likely mechanism involves two retroene eliminations of propene leading to vinylphosphaacetylene. Two mechanisms can account for the formation of HCP from vinylphosphaacetylene, either by a 1,2 or a 1,3 hydrogen shift. The first pathway was found to be the most favored kinetically. It is quite similar to the pathway proposed for the thermal decomposition of vinylacetylene into acetylene in the shock tube.     

Evidences on the intermediacy of furoxan in the flash vacuum thermolysis of some 4-Nitroisoxazoles

The kinetic measurements in the Flash Vacuum Thermolysis (FVT) of 3,5-Dimethyl- and 5-Methyl- 4-Nitroisoxazole confirm the already suggested intermediacy of the isomer 2H-Azirine in the formation of 1- Cyano-1-Nitroacetone. Moreover, theoretical calculations of the stabilization energy (E_s), at the transition state, using second order perturbation suggest that this azirine is formed through the isomer furoxan rather than directly from the starting isoxazole.     

A novel route to thioketenes by flash vacuum thermolysis of silylatedketene dithioacetals,synthesis of propadienethione.

Flash vacuum thermolysis (fvt) of silylated ketene dithioacetals 2 leads to reactive thioketenes 1. This method, added to a retrodienic reaction, allowedaccess to propadienethione 3.     

Synthesis of helianane, an unusual marine sesquiterpene employing ring-expansion by flash vacuum thermolysis

A total synthesis of the marine sesquiterpene helianane 1 is described involving the thermal rearrangement of the benzoxabicyclo[4.2.0]octenone 4 to generate the dienone 5 incorporating the benzoxocane ring system of 1. This dienone was converted to the key ketone 11, which on interaction with methylmagnesium iodide followed by hydrogenation of the resulting alkene 18 furnished helianane 1.     

Enzymic optical resolution and flash vacuum thermolysis in concert for the synthesis of optically active cyclopentenones

A practical synthesis of enantiomerically pure cyclopentenones with a predeterminated absolute configuration has been realized, starting from optically active tricyclo[5.2.1.0^2,6]decadienones.     

C64H6的结构和光谱的理论研究

本文用INDO系列方法研究了C64H6的结构与光谱, 表明C64H6有C2v和Cs两种稳定构型, 其中C2v构型能量较低, 讨论其加成及环加成产物对称性的规律并与13C NMR谱的实验结果相结合。计算了两种构型的电子光谱, 对电子跃迁进行了理论指认,并讨论了C64H6谱带红移的原因, 理论计算结果与实验事实基本吻合。     

Aryl-aryl bond formation by flash vacuum pyrolysis of benzannulated thiopyrans

In contrast to fully unsaturated 7-membered ring sulfur heterocycles (thiepines), some of which extrude sulfur and give the ring-contracted hydrocarbon even at room temperature in solution, benzannulated thiopyrans (6-membered sulfur heterocycles) require flash vacuum pyrolysis (FVP) conditions in the gas phase at temperatures in the range of 1000-1200 degrees C to promote the corresponding reaction. Thus, FVP of benzo[kl]thioxanthene (1) gives fluoranthene, and naphtho[2,1,8,7-klmn]thioxanthene (6) gives benzo[ghi]fluoranthene (7). FVP of thioxanthone (9) gives fluorenone (10), together with lesser amounts of dibenzo[b,d]thiophene (11), from competing decarbonylation.     

A theoretical study of C4H5N isomers: Comparison of cyano and isocyano as substituents

Ab initio molecular orbital calculations using a 3-21G basis set have been used to optimize geometries for pyrrole, CH₃(X)CCH₂, CH₃(H)CCHX (both cis and trans), c-C₃H₅X, and CH₂CHCH₂X, where X is CN and NC. In all the alkenyl derivatives methyl groups are found to adopt the conformation in which the methyl hydrogen eclipses the double bond. 6-31G*∥3-21G level calculations show the alkenyl cyanides to be of similar energy to pyrrole, but the isocyanides are ～20 kcal mol^?1 higher in energy. For both substituents the cyclopropyl derivatives are higher in energy by ～10 kcal mol^?1. At the 6-31G* level ring strain is 27.7 kcal mol^?1 for the cyanide and 30.6 kcal mol^?1 for the isocyanide. Data on the relative energies of RCN and RNC are compared when R is (i) a saturated hydrocarbon, (ii) an unsaturated hydrocarbon, (iii) an α-carbenium ion, (iv) an allyl cation, and (v) an α-carbanion.     

A theoretical study of the reaction of HCO+ with C2H2

A theoretical study was performed for the reaction of formyl cation and acetylene to give C₃H+O in flames and C₂H (nonclassical)+CO, both in flames and in interstellar clouds. The corresponding Potential Energy Surface (PES) was studied at the B3LYP/cc‐pVTZ level of theory, and single‐point calculations on the B3LYP geometries were carried out at the CCSD(T)/cc‐pVTZ level. Our results display a route to propynal evolving energetically under C₂H (nonclassical)+CO and, consequently, accessible in interstellar clouds conditions. This route connects the most stable C₃H₃O⁺ isomer (C2‐protonated propadienone) with a species from which propynal may be produced in a dissociative electron recombination reaction. The reaction channel to produce the C₃H+O evolves basically through two TSs and presents an endothermicity of 63.9 kcal/mol at 2000 K. According to our Gibbs energy profiles, the C2‐protonated propadienone is the most stable species at low–moderate temperatures and, consequently, could play a certain role in interstellar chemistry. On the contrary, in combustion chemistry conditions (2000 K) the C₂H (nonclassical)+CO products are the most thermodynamically favored species. © 2000 John Wiley & Sons, Inc. J Comput Chem 21: 35–42, 2000     

A theoretical study of the TiC5 cluster

The geometric and electronic properties of the titanium carbide TiC(5) cluster in its neutral and anionic charge states have been investigated using density functional theory (DFT) at the B3LYP level. The nonplanar six-membered ring-type or "butterflylike" structures are found to be the equilibrium geometric structures of TiC(5) and TiC(5) (-). Time-dependent DFT is used in the calculation of the excited states. The theoretical assignment at the B3LYP level for the features in the photoelectron spectrum is given. All results obtained are in good agreement with the available experimental data.     

Experimental and theoretical studying the thermolysis of nitrate

This paper presents calorimeter measurement for the thermal decomposition of n-propyl nitrate (NPN), isopropyl nitrate (IPN) and 2-ethylhexyl nitrate (EHN). Similar experimental results of triethylene glycol dinitrate (tri-EGDN) and tetraethylene glycol dinitrate (tetra-EGDN) are included for comparison. The potential energy surfaces (PESs) along O-NO₂ bond stretch are investigated using the DFT (B3P86, B3PW91 and B3LYP), ab initio Hartree-Fock and PM3 methods. The good coincidence of experimental with theoretical results indicates that initial stage in the thermal decomposition of five nitrates is only unimolecular homolytical dissociation of the O-NO₂ bonds and the activation energies of thermolysis by DSC correspond to the energies of O-NO₂ bond scission of nitrates.     

Isomerization study of C5H5NO molecules

The complex potential energy surface (PES) for the isomerization of C₅H₅NO species, including 18 isomers and 23 interconversion transition states, is probed theoretically at the B3LYP/6‐311++G(d,p) and MP2//B3LYP/6‐311++G(d,p) levels of theory. The geometries and relative energies for various stationary points were determined. The zero‐point vibrational energy (ZPVE) corrections have been made to calculate the reliable energy. We predicted a six‐membered ring structure as a global minima isomer I, which is 118.49 and 131.48 kcal · mol^?1 more stable than the least stable, four‐ and three‐membered ring isomer VIII at B3LYP and MP2//B3LYP levels of theory, respectively. The isomers and interconversion transition states have verified by frequency calculation. The intrinsic reaction coordinates (IRC) calculations have been performed to confirm that each transition state is linked by the desired reactants and products. The isomer stability has been studied using relative energies, chemical hardness, and chemical potential. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

Thermochemistry of disputed soot formation intermediates C4H3 and C4H5

Accurate isomeric energy differences and standard enthalpies of formation for disputed intermediates in soot formation, C(4)H(3) and C(4)H(5), have been determined through systematic extrapolations of ab initio energies. Electron correlation has been included through second-order Z-averaged perturbation theory (ZAPT2), and spin-restricted, open-shell coupled-cluster methods through triple excitations [ROCCSD, ROCCSD(T), and ROCCSDT] utilizing the correlation-consistent hierarchy of basis sets, cc-pVXZ (X = D, T, Q, 5, and 6), followed by extrapolations to the complete basis set limit via the focal point method of Allen and co-workers. Reference geometries were fully optimized at the ROCCSD(T) level with a TZ(2d1f,2p1d) basis set. Our analysis finds that the resonance-stabilized i-C(4)H(3) and i-C(4)H(5) isomers lie 11.8 and 10.7 kcal mol(-1) below E-n-C(4)H(3) and E-n-C(4)H(5), respectively, several kcal mol(-1) (more, less) than reported in recent (diffusion Monte Carlo, B3LYP density-functional) studies. Moreover, in these systems Gaussian-3 (G3) theory suffers from large spin contamination in electronic wave functions, poor reference geometries, and anomalous vibrational frequencies, but fortuitous cancellation of these sizable errors leads to isomerization energies apparently accurate to 1 kcal mol(-1). Using focal-point extrapolations for isodesmic reactions, we determine the enthalpies of formation (delta(f)H(0) (composite function)) for i-C(4)H(3), Z-n-C(4)H(3), E-n-C(4)H(3), i-C(4)H(5), Z-n-C(4)H(5), and E-n-C(4)H(5) to be 119.0, 130.8, 130.8, 78.4, 89.7, and 89.1 kcal mol(-1), respectively. These definitive values remove any remaining uncertainty surrounding the thermochemistry of these isomers in combustion models, allowing for better assessment of whether even-carbon pathways contribute to soot formation.     

Novel products from C6H5 + C6H6/C6H5 reactions

To date only one product, biphenyl, has been reported to be produced from C(6)H(5) + C(6)H(6)/C(6)H(5) reactions. In this study, we have investigated some unique products of C(6)H(5) + C(6)H(6)/C(6)H(5) reactions via both experimental observation and theoretical modeling. In the experimental study, gas-phase reaction products produced from the pyrolysis of selected aromatics and aromatic/acetylene mixtures were detected by an in situ technique, vacuum ultraviolet (VUV) single photon ionization (SPI) time-of-flight mass spectrometry (TOFMS). The mass spectra revealed a remarkable correlation in mass peaks at m/z = 154 {C(12)H(10) (biphenyl)} and m/z = 152 {C(12)H(8) (?)}. It also demonstrated an unexpected correlation among the HACA (hydrogen abstraction and acetylene addition) products at m/z = 78, 102, 128, 152, and 176. The analysis of formation routes of products suggested the contribution of some other isomers in addition to a well-known candidate, acenaphthylene, in the mass peak at m/z = 152 (C(12)H(8)). Considering the difficulties of identifying the contributing isomers from an observed mass number peak, quantum chemical calculations for the above-mentioned reactions were performed. As a result, cyclopenta[a]indene, as-indacene, s-indacene, biphenylene, acenaphthylene, and naphthalene appeared as novel products, produced from the possible channels of C(6)H(5) + C(6)H(6)/C(6)H(5) reactions rather than from their previously reported formation pathways. The most notable point is the production of acenaphthylene and naphthalene from C(6)H(5) + C(6)H(6)/C(6)H(5) reactions via the PAC (phenyl addition-cyclization) mechanism because, until now, both of them have been thought to be formed via the HACA routes. In this way, this study has paved the way for exploring alternative paths for other inefficient HACA routes using the PAC mechanism.