Isomerization of unsaturated radicals. VI. Isomerization of 3-cyclopenlenyl and pentamethylene radicals

The 184.9 nm photochemistry 0f gaseous 3-methylcyclopentene and 3-methyl-1,4-pentadiene have been studied. Both photoexcited species decompose mainly through the primayy rupture of the C-CH₃ bond. Vibrationally excited 3-cyclopenennyl and pentamethylene radicals are formed in the primayy decomposition in the former and latter systems respectively. These radicals are connected through isomerization reactions: in the presence of DI, the isomers cyclopenten,, and trans-1,3-pentadtene and/or vinylcyclopropane are formed in both systems. The quantum yields depend on the pressure and the starting monomer: cyclopentene and cyclopentadiene are the major products from the photolysis of 3-methylcyclopentene + DI mixtures and only minor quantities of the other C₅H₈ compounds are formed. Cyclopentadiene is the major product of the photolysis of 3-methyl-1,4-pentadiene + O₂ mixtures whereas vinylcyclopropane and trans-1,3-pentadiene are the major C₅ producss of the photolysis of 3-methyl-1,4-pentadiene + DI mixtures. The geometries of 3-cyclopentenyl and of the structures at the six critical points in the torsional potential energy curve (TPEC) for rotation about the 2- and 3-C-C bonds in the open chain pentamethylene species have been optimized completely by ab initio RHF-SCF gradient methods. For the open-chain structures the bond orders, bond lengths and the free valence (primarily associated with the central carbon atom) all correspond to 1,4-pentadien-3-yl conformations. In the ground state there is a high barrier to formation of 3-cyclopentenyl from 1,4-pentadien-3-yl. The features (relative energies and torsionll barriers) of the TPEC for 1,4-pentadien-3-yl explain the ESR observations for the open chain C₅H₇ radical rotamers.     

Isomer distinction by ion/molecule reactions in an ion trap: The case of C5H8

Isomeric C₅H₈ compounds are distinguished by monitoring the products of their reactions with mass-selected ions generated from the individual isomers. This procedure, done by selecting appropriate reaction times in a quadrupole ion trap, yields data for the compounds which are more structure-selective than those obtained by collision-induced dissociation or dissociative charge stripping, both procedures in which isomer distinction is based on the behavior of the molecular ions rather than the neutral molecules themselves. All isomers except cis and trans 1,3-pentadiene can be distinguished by their ion/molecule reactions. The conjugated dienes, 1,3-pentadiene and isoprene, form the deprotonated C₁₀H₁₅⁺ dimer which is not generated by 1,4-pentadiene, cyclopentene, or by the allenes, 2,3-pentadiene and 3-methyl-1,2-butadiene. This clear, qualitative difference enables the isomers 1,4- and 1,3-pentadiene to be distinguished, which is otherwise difficult.     

Reaction of atomic oxygen with cyclopentadiene

The reaction of 1,3-cyclopentadiene (CPD) with ground-state atomic oxygen O(³P), produced by mercury photosensitized decomposition of nitrous oxide, was studied. The identified products were carbon monoxide and the following C₄H₆ isomers: 3-methylcyclopropene, 1,3-butadiene, 1,2-butadiene, and 1-butyne. The yield of carbon monoxide over oxygen atoms produced (?_CO) was equal to the sum of the yields of C₄H₆ isomers in any experiment. ?_CO was 0.43 at the total pressure of 6.5 torr and 0.20 at 500 torr. We did not succeed in detecting any addition products such as C₅H₆O isomers. It was found that 3-methylcyclopropene was produced with excess energy and was partly isomerized to other C₄H₆ isomers, especially to 1-butyne. The excess energy was estimated to be about 50 kcal/mol. The rate coefficient of the reaction was obtained relative to those for the reactions of atomic oxygen with trans-2-butene and 1-butene. The ratios k_CPD+O/k_{trans-2-butene+O}= 2.34 and k_CPD+O/k_1-butene+O = 11.3 were obtained. Probable reaction mechanisms and intermediates are suggested.     

The formation of [C9H10]+˙ ions by loss of a molecule of water from molecular ions of 3-phenylpropanol with lifetimes of 10−11 to 10−5 s

Field ionization kinetic experiments in conjunction with deuterium labelling have been shown that the molecular ions of 3-phenylpropanol with lifetimes as short as 10^?11s lose a molecule of water via a specific 1,3 elimination. At times > 10^?11s two distinct hydrogen interchange processes in the molecular ions appear to complete with this reaction. One of the intechange processes involves the benzylic and hydroxylic hydrogen atoms and starts to complete with the elimination of water at shorter molecular ion lifetimes than the other interchange process in which the ortho hydrogen atoms also participate. Decomposing [C₉H₁₀]^+˙ ions generated by elimination of water from the molecular ions of 3-phenylpropanol or by direct ionization of various isomeric C₉H₁₀ compounds could not be distinguished adequately, illustrating isomerization either to a common ion structure or to a set of ions with rapidly interconverting structures. A consideration of the energetics of the elimination of water from 3-phenylpropanol suggests that at threshold energies 1-phenylpropene or indane type structures can be formed. Arguments for the latter have been obtained from the observation that a labile fluorine atom is present in the [M – H₂O]^+˙ ions generated from 3-pentafluoro-phenylpropanol.     

Interaction of dioxygen with the platinum Pt19/SnO2/H2 cluster: DFT calculation

The adsorption of the O₂ molecule onto the surface of the Pt₁₉ platinum cluster deposited onto the tin dioxide crystal surface in the presence of dissociated hydrogen molecule has been calculated by the density functional theory method within the generalized gradient approximation (GGA-PBE) with periodic boundary conditions and a projector-augmented plane-wave (PAW) basis set. It has been demonstrated that the oxygen molecule can be adsorbed without a barrier onto the free surface of the Pt₁₉/SnO₂/H₂ cluster to form a superoxy isomer with one Pt-O bond (the energy of elimination of the oxygen molecule is 0.75 eV), which converts almost without a barrier to more stable peroxide isomers with two Pt-O bonds (the energy of elimination of the O₂ molecule is 1.2?1.7 eV). The energy of elimination of the oxygen molecule from the isomers with two-coordinated oxygen positions at the cluster edges is 2.10?2.53 eV. The isomers with mono- and tricoordinated oxygen positions are less energetically favorable than the isomers with two-coordinated oxygen positions. The process of addition of the oxygen molecule to the platinum cluster and elimination of the water molecule formed in the reaction Pt₁₉/SnO₂/H₂ + O₂ → Pt₁₉/SnO₂/O + H₂O is energetically favorable by 1.6 eV.     

The thermal reaction of 2-pentene around 500°C at low extent of reaction

The thermal reaction of 2-pentene (cis or trans) has been performed in a static system over the temperature range of 470°–535°C at low extent of reaction and for initial pressures of 20–100 torr. The main products of decomposition are methane and 1,3-butadiene. Other minor primary products have been monitored: trans-2-pentene, trans- and cis-2-butenes, ethane, 1,3-pentadienes, 3-methyl-1-butene, propylene, 1-butene, hydrogen, ethylene, and 1-pentene. The initial orders of formation, 0.8–1.1 for most of the products and 1.5–1.8 for 1-pentene, increase with temperature. The formation of the products and the influence of temperature on their orders can be essentially explained by a free radical chain mechanism. But cis–trans or trans–cis isomerization and hydrogen elimination from cis-2-pentene certainly involve both molecular and free radical processes. The formation of 1-pentene mainly occurs from the abstraction of the hydrogen atom of 2-pentene by resonance stabilized free radicals (C₅H₉.).     

Diacetoxylation of conjugated dienes with thallium(III) acetate in acetic acid

The reaction of conjugated dienes such as 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, 2,5-dimethyl-2,4-hexadiene, 1,3-cyclopentadiene, and 1,3-cyclohexadiene, with thallium(III)acetate in acetic acid at 10–65° for 0.5–15 hr affords an isomeric mixture of the corresponding diacetoxyalkenes (1,2- and 1,4-addition products) in 10–92% yields. The 1,2-addition products are predominantly formed in all cases examined except the case of 1,3-cyclopentadiene. The reaction is assumed to proceed through acetoxythallation and dethallation steps, the latter step being accompanied and/or followed by an attack of acetoxyl group. An initial attack of thallium moiety is proposed to occur mainly at C-1 and C-2 carbons in the cases of linear terminal dienes and cyclic dienes, respectively.     

CO2 laser-induced photolysis of spirohexane: Time resolved observation of vibrationally excited 1,3-butadiene

Vibrationally excited spirohexane (SHX) generated in CO₂ laser irradiation undergoes photolysis producing ethylene, 1,3-butadiene and a C₄ compound as major products. Collisional energy pooling plays a major role in the multiphoton excitation process. Time-resolved formation of 1,3-butadiene is monitored by UV absorption from which the unimolecular rate constant for SHX dissociation is found to be 5.6 × 10⁵ s⁻¹. A red shift of 4O nm observed in the transient UV absorption spectrum has been assigned to nascent 1,3-butadiene, which suggests that vibrationally hot 1,3-butadiene molecules are formed. The effects of laser energy fluence and pressure of SF₆ as a sensitizer on dissociation yield are also investigated.     

Vinylation and polymerization with trivinylaluminum. I. Vinylation of organic halides as a model for termination in cationic polymerization leading to vinyl end groups

An improved synthesis of trivinylaluminum (V₃Al) is described. The proton magnetic resonance (PMR) spectrum of V₃Al was recorded and analyzed. A new vinylation method involving the use of V₃Al as the vinylating agent has been developed, and the vinylation of organic halides by V₃Al was studied at ?30, ?50 and ?70°C. Primary alkyl chlorides, such as methyl and methylene chloride, do not react with V₃Al and were used as solvents. Secondary chlorides such as 2-chloropropane also do not react. t-Butyl chloride gives rise to t-butylethylene (70–98%), depending on reaction conditions, and the allylic chlorides, 3-chloro-1-butene, and 3-chloro-3-methyl-1-butene, yield the expected vinylated products and their isomers (～90%). Allyl and benzyl chloride do not react under the conditions tried. The reaction between V₃Al and the ditertiary dichloride 2,6-dichloro-2,6-dimethylheptane yields several isomeric C₁₃H₂₄ and C₁₁H₂₀ hydrocarbons; however, surprisingly, C₉H₁₆ does not form. The C₁₃ hydrocarbons arise by divinylation at the termini of the dichloride, while the C₁₁ hydrocarbons are formed by vinylation at one and proton elimination at the other terminus of the dichloride. The presence of unsaturated C₁₃H₂₄ and C₁₁H₂₀ isomers is most likely due to proton induced isomerization. These results are explained by a proximity effect involving vinylation at one end of the dichloride by V₃Al followed by rapid reaction of the second chlorine (mostly) by V₂AlCl generated in situ during the first vinylation in the proximity of the chloride. At the other chlorine terminus V₂AlCl causes either a second vinylation (leading to C₁₃ hydrocarbons) or a proton elimination (leading to C₁₁ hydrocarbons). The absence of C₉H₁₆ among the reaction products indicates that V₃Al exclusively effects vinylation. The RCl + V₃Al ← RV + V₂AlCl reaction may be regarded as a model for initiation followed by immediate termination in cationic olefin polymerization, a process leading to vinyl-ended polymers.     

1-(Pyrimidin-4-yl)pyrazol-5(4<Emphasis Type="Italic">H</Emphasis>)-one derivatives: II. Electrophilic substitution in 5-hydroxy-3-methyl-1-(6-methyl-2-methylsulfanylpyrimidin-4-yl)-1<Emphasis Type="Italic">H</Emphasis>-pyrazole

Electrophilic substitution of hydrogen in bicyclic 5-hydroxy-3-methyl-1-(6-methyl-2-methylsulfanylpyrimidin-4-yl)-1H-pyrazole occurs exclusively at the C⁴ atom of the five-membered heteroring. Unstable electrophilic substitution products are stabilized via addition of the second substrate molecule with formation of bridged adducts.     

Theoretical studies on structures and UV-Vis spectra of C70O

Systematic studies on eight isomers of C₇₀O were performed by means of INDO methods. It has been indicated that the O atom is mainly added to the C₁-C₂ or C₃-C₃ bond and an epoxide feature with C_s symmetry is formed. Based on the optimized geometries, the UV-Vis spectra were calculated. It has been found that the main peaks of C₇₀O resemble those of C₇₀ and the characteristic absorptions beyond 460 nm are produced, which is in agreement with the experimental results. Theoretical assignments about the absorptions were canied out and the reason for the red-shift of the absorptions was discussed. C₇₀O is probably composed of four isomers according to the calculated results. Project supported by the National Natural Science Foundation of China.     

Spectrophotometric and x-ray crystallographic studies of 1-carbamoylbenz-[c,d]indol-2-ones

On the basis of a measurement of the frequencies and intensities of the stretching vibrations of the amino, amido, and ester groups in the IR spectra, it was established that products of the reaction of N-benzenesulfonylhydroxynaphthalimides with ammonia in alcohol solutipns have a structure of the type of 1-carbamoylbenz[c,d]-indol-2-ones and are not molecules with a seven-membered heterocycle, by analogy with 3-oxido-2-alkylnaphtho[1,8-d,e][1,3] oxoniazepin-1-ones. A determination of the molecular and crystal structure of one of these compounds (C₁₃H₁₀N₂O₂) confirmed this conclusion: The molecule is 1-(N-methylcarbamoyl)benz[c,d]indol-2-one. In the naphthalene ring of the molecule the bond angles at the central bond are deformed analogously to that found in acenaphthene. The intramolecular hydrogen bond O···HN closes a six-membered ring in the molecule. The crystal is constructed from dimers formed by intermolecular hydrogen bonds O···HN.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1110–1114, August, 1984.     

Reciprocal Tests of Steric Opposition to Down-Disrotatory ThermalDecyclization of [3.2.1] Propellanes. The Cycloreversion Stereochemistry of the 6,7,8-Trimethyltricyclo[3.2.1.01,5] octanes

The syntheses and thermal decompositions of the isomeric title compounds are described. The cis, endo isomers undergo down-disrotatory cycloreversion to E,E-2-methyl-1,3-bis-(ethylidene)-cyclohexane with high stereospecificity, regardless of the stereochemistry of the C₈-methyl group. Both 8-syn - and 8-anti - 6,7-trans -trimethyl isomers decyclize with low stereochemical preference,suggesting that the orbital overlap factors favoring the down-disrotatory path in the cis cases may be overcome easily by steric effects.     

Thermal decomposition products of methyl 1,5-diphenyl- and 5-methyl-1-phenyl-2,3-diazabicyclo[3.1.0]hex-2-ene-6-exo-carboxylates

Methyl 1,5-diphenyl- and 5-methyl-1-phenyl-2,3-diazabicyclo[3.1.0]hex-2-ene-6-exo-carboxylates at 138°C undergo decomposition via elimination of nitrogen molecule with formation in each case of five products. Two products are methyl 1,3-diphenyl(or 1-methyl-3-phenyl)bicyclo[1.1.0]butane-2-endo- and -exo-carboxylates, and the three others are derivatives of buta-1,3-diene, methyl (Z)-2-benzylidene-3-phenyl(or 3-methyl)but-3-enoate and methyl (E)- and (Z)-3,4-diphenyl(or 4-methyl-3-phenyl)penta-2,4-dienoates. The formation of these products may be rationalized assuming intermediacy of substituted allylcarbene which undergoes both intramolecular cycloaddition and rearrangements involving 1,2-hydride and 1,2-vinyl shifts.     

Photodynamic Activity of Fullerene Derivatives Solubilized in Water by Natural-Product-Based Solubilizing Agents

Water-soluble fullerenes prepared by using solubilizing agents based on natural products are promising photosensitizers for photodynamic therapy. Cyclodextrin, β-1,3-glucan, lysozyme, and liposomes can stably solubilize not only C₆₀ and C₇₀, but also some C₆₀ derivatives in water. To improve the solubilities of fullerenes, specific methods have been developed for each solubilizing agent. Water-soluble C₆₀ and C₇₀ exhibit photoinduced cytotoxicity under near-ultraviolet irradiation, but not at wavelengths over 600 nm, which are the appropriate wavelengths for photodynamic therapy. However, dyad complexes of solubilized C₆₀ derivatives combined with light-harvesting antenna molecules improve the photoinduced cytotoxicities at wavelengths over 600 nm. Furthermore, controlling the fullerene and antenna molecule positions within the solubilizing agents affects the performance of the photosensitizer.     

Gas Phase Reaction of Tetrachlorogermane with Conjugated Dienes in the Presence of Hexachlorodisilane Initiator

Studies of the reaction of GeCl₄ with acyclic conjugated dienes (1,3-butadiene, 2-methyl-1,3- butadiene, 2,3-dimethyl-1,3-butadiene) and cyclopentadiene in the presence of Si₂Cl₆ initiator were carried out. With acyclic dienes, corresponding 1,1-dichloro-1-germacyclo-3-pentenes and 1,1-dichloro-1-silacyclo-3- pentenes are preferrably formed. With cyclopentadiene the main reaction products are cyclopentenyltrichlorogermanes and cyclopentenyltrichlorosilanes formed respectively by hydrogermylation and hydrosilylation of the starting diene. The explanation of the established rule is offered.     

Specifically π→π* Induced Photoreactions of α,β-Unsaturated Ketones: Hydrogen Abstraction by the α-carbon. (Preliminary Communication)

Irradiations at 254 nm of the α,β-unsaturated γ-dimethoxy-methyl ketone 7 in iso-octane and t-butyl alcohol afforded in a specifically π→π*induced process and in high chemical yield the epimeric products 9 and 10 . These products were not formed on n→π* excitation of 7 at > 340 nm, but triplet energy transfer to 1,3-cyclohexadiene could be observed. Photolyses of the hexadeuterio analog 7-d₆ at 254 nm led to the fully deuteriated products (cf. 9-d₆ ) in both solvents, with stereospecific incorporation of a deuterium atom in position C(1α). The structures of 9 and 10 were determined by an X-ray diffraction analysis of 9 and chemical correlations of the two products. The structural constraints in 7 demand a hitherto unprecedented direct transfer of a methoxyl hydrogen to the α-carbon of the excited enone and formation of intermediate 8 .     

Formation of unsaturated bicyclic γ-butyrolactone by oxidative dimerization of 2-methyl-2-ethynylcyclopropanecarboxylic acid

Conclusions The oxidative dimerization of a mixture of the trans and cis isomers of 2-methyl-2-ethynylcyclopropanecarboxylic acid in the presence of CuCl and NH₄Cl gives, along with bis(trans-1-methyl-2-carboxyl-1-cyclopropyl)diacetylene (53% yield), also the corresponding dilactone, and specifically bi(1-methyl-4-oxo-3-oxabicyclo[3.1.0]-2-hexalidene)methyl (14% yield), which is probably formed via the intramolecular cyclization of the intermediately formed bis(cis-1-methyl-2-carboxy-1-cyclopropyl) diacetylene.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 5, pp. 1164–1166, May, 1981.     

Gas‐Phase Synthesis of the Benzyl Radical (C6H5CH2)

Dicarbon (C₂), the simplest bare carbon molecule, is ubiquitous in the interstellar medium and in combustion flames. A gas‐phase synthesis is presented of the benzyl radical (C₆H₅CH₂) by the crossed molecular beam reaction of dicarbon, C₂(X¹Σ_g⁺, a³Π_u), with 2‐methyl‐1,3‐butadiene (isoprene; C₅H₈; X¹A′) accessing the triplet and singlet C₇H₈ potential energy surfaces (PESs) under single collision conditions. The experimental data combined with ab initio and statistical calculations reveal the underlying reaction mechanism and chemical dynamics. On the singlet and triplet surfaces, the reactions involve indirect scattering dynamics and are initiated by the barrierless addition of dicarbon to the carbon–carbon double bond of the 2‐methyl‐1,3‐butadiene molecule. These initial addition complexes rearrange via multiple isomerization steps, leading eventually to the formation of C₇H₇ radical species through atomic hydrogen elimination. The benzyl radical (C₆H₅CH₂), the thermodynamically most stable C₇H₇ isomer, is determined as the major product.     

Stereochemical studies. Part 67. Saturated heterocycles. Part 52. The mass spectra of some condensed skeleton 1,3-oxazin-4-one derivatives

The mass spectrometric behaviour of twenty saturated heterocyclic compounds with a 1,3-oxazin-4-one moiety fused with cis or trans anellation to a cycloalkane ring (C₅-C₈) was studied. The roles of the C-2 and N-3 substituent(s) were found to be characteristic, while the size of the cycloalkane ring seemed to be unimportant. Some fragmentation processes involving breakdown of the oxazinone ring of the cis or trans isomers displayed significant stereoselectivity. A striking new decomposition process involving significant chlorine elimination from the molecular ion of some 2-p-chlorophenyl derivatives was observed and was studied in some detail.