Thermodynamic and kinetic issues in the formation and oxidation of aromatic species

The chemistry of aromatic species is discussed in the context of detailed kinetic modelling of benzene and butadiene flames and stirred reactors featuring ethylene and mixed aromatic/ethylene/hydrogen fuels. The development of reliable detailed mechanisms depends on the accuracy of the underlying hydrocarbon chemistry and the present paper highlights some current issues in the formation and oxidation of aromatics. In particular, uncertainties pertaining to the rates and product distributions of a range of possible naphthalene and indene formation sequences are discussed from the basis of improved predictions of key intermediates. The naphthalene formation paths considered include initiation via C5H5 + C5H5, C6H5 + C4H4 and C7H7 + C3H3 reactions and results are assessed in the context of a number of tentative detailed and simplified sequences. It is shown that a number of possible formation channels are plausible and that their relative importance is strongly dependent upon oxidation conditions. Particular emphasis is placed on the investigation of formation paths leading to isomeric C9H8 structures. The latter are typically ignored despite measured concentrations similar to those of naphthalene. The rates of formation of C9H8 compounds are consistent with sequences initiated by C6H5 + C3H3 and C6H5 + C3H4 leading to indene through repeated isomerisation reactions. The current work also shows that reactions of the type C9H7 + CH3 and C9H7 + 3CH2 provide a mass growth source that link five and six member ring structures.     

An ab initio G3-type/statistical theory study of the formation of indene in combustion flames. II. The pathways originating from reactions of cyclic C5 species-cyclopentadiene and cyclopentadienyl radicals

Chemically accurate ab initio Gaussian-3-type calculations of various rearrangements on the C10H11 potential energy surface have been performed to investigate the indene formation mechanism originating from the reactions of two abundant cyclic C5 species, cyclopentadiene and cyclopentadienyl radicals. Using the accurate ab initio data, statistical theory calculations have been applied to obtain high-pressure-limit thermal rate constants within the 300-3000 K temperature range, followed by calculations of relative product yields. Totally, 12 reaction pathways leading to indene and several azulene precursors, 1,5-, 1,7-, 1,8a-, and 1,3a-dihydroazulene, have been mapped out, and the relative contributions of each pathway to the formation of reaction products have been estimated. At temperatures relevant to combustion, the indene has been found as the major reaction product (>50%) followed by 1,5-dihydroazulene (25-35%), whereas all other products demonstrate either minor or negligible yields. The results of the present study have been combined with our previous data for rearrangements of the 9-H-fulvalenyl radical on the C10H9 potential energy surface to draw the detailed picture of radical-promoted reaction mechanisms leading from c-C5 species to the production of indene, naphthalene, azulene, and fulvalene in combustion. The suggested mechanism and computed product yields are consistent with the experimental data obtained in the low-temperature pyrolysis of cyclopentadiene, where indene and naphthalene have been found as the major reaction products.     

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.     

Synthesis of poly(indene carbonate) from indene oxide and carbon dioxide--a polycarbonate with a rigid backbone

The catalytic coupling of carbon dioxide with indene oxide utilizing (salen)Co(III)-2,4-dinitrophenoxide in the presence of an onium salt is presented. X-ray structural data for indene oxide monomer as well as cis-indene carbonate display near planarity of the fused cyclopentene and benzene rings. Low temperature (0 °C) is required to selectively afford copolymer vs cyclic carbonate from the coupling reactions of CO(2) and indene oxide. The produced poly(indene carbonate) samples have molecular weights of up to 7100 Da, with corresponding glass transition temperatures of up to 134 °C, the highest yet reported for polycarbonates produced from CO(2)/epoxides coupling. Poly(indene carbonate) is thermally stable up to 249 °C. The polymerizations are well controlled, with PDI values ≤1.3.     

Formation of naphthalene, indene, and benzene from cyclopentadiene pyrolysis: a DFT study

Four new reaction pathways for polycyclic aromatic hydrocarbon growth from cyclopentadiene pyrolysis are proposed and investigated using the B3LYP/6-31G(d,p) level of theory. These pathways allow for the production of indene, naphthalene, and benzene through intramolecular addition, C-H beta-scission, and C-C beta-scission reaction mechanisms, respectively. Results show that the intramolecular addition channel is favored at low temperatures, and the C-H beta-scission channel and the newly identified C-C beta-scission pathway become significant when the temperature increases. These results are in qualitative agreement with the experimental results previously obtained by this research group indicating that the main product at low temperature is indene, while benzene and naphthalene production dominate at the high-temperature end.     

High pressure pyrolysis of toluene. 2. Modeling benzyl decomposition and formation of soot precursors

The pyrolysis of toluene, the simplest methyl-substituted aromatic molecule, has been studied behind reflected shock waves using a single pulse shock tube. Part 1 in this two-part series focused on the high-pressure experimental results and the high-pressure limiting rate coefficients for the primary steps in toluene decomposition. The present work focuses on the modeling of benzyl decomposition and the growth of key soot precursors (C2H2, C4H2, C8H6, and indene) from toluene pyrolysis with 81 among the 262 reactions in the detailed toluene model representing the chemistry that describes the formation and decomposition of these species. Feasible pathways for benzyl decomposition as well as phenylacetylene and indene formation have been tested. The simulations also show very good agreement with the single pulse shock tube profiles for the growth of key soot precursors such as C2H2, C4H2, C8H6, and indene.     

Gold-catalyzed ketene dual functionalization and mechanistic insights: divergent synthesis of indenes and benzo[d]oxepines

An unprecedented gold-catalyzed ketene C=O/C=C bifunctionalization method has been developed. Mechanistic studies and density function theory(DFT) calculations indicate that the reaction is initiated by gold-catalyzed Wolff rearrangement of diazoketone to form the ketene intermediate, followed by intermolecular nucleophilic addition and terminated with two divergent cyclization processes via enol intermediates. In the case with alcohols as the nucleophiles, the reaction goes through a C-5-endodig carbocyclization to give the indene products; whereas, O-7-endo-dig cyclization occurs dominantly when indoles/pyrroles are used as the nucleophiles, delivering the 7-membered benzo[d]oxepines. In comparison with the well-documented cycloaddition and nucleophilic addition reactions, this cascade reaction features a novel reaction pattern for the ketene dual functionalization through addition with nucleophile and electrophile in sequence.     

Mechanistic studies on the Cu-catalyzed three-component reactions of sulfonyl azides, 1-alkynes and amines, alcohols, or water: dichotomy via a common pathway

Combined analyses of experimental and computational studies on the Cu-catalyzed three-component reactions of sulfonyl azides, terminal alkynes and amines, alcohols, or water are described. A range of experimental data including product distribution ratio and trapping of key intermediates support the validity of a common pathway in the reaction of 1-alkynes and two distinct types of azides substituted with sulfonyl and aryl(alkyl) groups. The proposal that bimolecular cycloaddition reactions take place initially between triple bonds and sulfonyl azides to give N-sulfonyl triazolyl copper intermediates was verified by a trapping experiment. The main reason for the different outcome from reactions between sulfonyl and aryl(alkyl) azides is attributed to the lability of the N-sulfonyl triazolyl copper intermediates. These species are readily rearranged to another key intermediate, ketenimine, into which various nucleophiles such as amines, alcohols, or water add to afford the three-component coupled products: amidines, imidates, or amides, respectively. In addition, the proposed mechanistic framework is in good agreement with the obtained kinetics and competition studies. A computational study (B3LYP/LACV3P*+) was also performed confirming the proposed mechanistic pathway that the triazolyl copper intermediate plays as a branching point to dictate the product distribution.     

Reaction of aminodihydropentalenes with HB(C6F5)2: the crucial role of dihydrogen elimination

The aminodihydropentalene derivative 1a reacts with the Lewis acidic RB(C(6)F(5))(2) boranes (2a-c) by C-C bond cleavage to yield the formal borylene insertion products 3. In contrast, 1a,b react with HB(C(6)F(5))(2) at 55 °C by elimination of dihydrogen to yield the iminium-stabilized zwitterionic heterofulvenes 10a,b. The reaction pathways were studied by preparation of the kinetically controlled intermediates 7a,b and the thermodynamically controlled products 9a,b, monitored by variable-temperature NMR experiments, and supported by DFT calculations. The trapping reactions of 9a with HCl and PhCHO, respectively, led to the addition products 13 and 14. Compounds 3c, 7a,b, 10a,b, 11, 13, and 14 were characterized by X-ray diffraction.     

A combined theoretical and experimental study of efficient and fast titanocene-catalyzed 3-exo cyclizations

The mechanism of titanocene mediated 3-exo cyclizations was investigated by a combined theoretical and experimental study. A gradient corrected density functional theory (DFT) method has been scaled against titanocene dichloride, the parent butenyl radical, and in bond dissociation energy (BDE) calculations. The BP86 method using density fitting, and a basis set of triple-zeta quality emerged as a highly reliable tool for studying titanocene mediated radical reactions. The computational results revealed important kinetic and thermodynamic features of cyclopropane formation. Surprisingly, the beta-titanoxy radicals, the first intermediates of our investigations, were demonstrated to possess essentially the same thermodynamic stabilization as the corresponding alkyl radicals by comparison of the calculated BDEs. In contrast to suggestions for samarium mediated reactions, the cyclization was shown to be thermodynamically favorable in agreement with earlier kinetic studies. It was established that stereoselectivity of the cyclization is governed by the stability of the intermediates and thus the trans disubstituted products are formed preferentially. The observed ratios of products are in good to excellent agreement with the DFT results. By a combination of computational and experimental results, it was also shown that for the completion of the overall cyclopropane formation the efficiency of the trapping of the cyclopropylcarbinyl radicals is decisive.     

Transition metal-catalyzed pentannulation of propargyl acetates via styrylcarbene intermediates

The indene formation from phenyl-substituted sec- and tert-propargyl esters (terminal alkynes) was achieved by platinum or ruthenium catalysis via E-vinylcarbenoid intermediate. Considering the competitive reactions of pentannulation versus cyclopropanation, the equilibrium ratios of E and Z vinylcarbenoid intermediates from sec- and tert-propargyl esters are estimated at ca. 10:90 and 40:60, respectively. Two reaction pathways, Nazarov-type cyclization and/or metallacycle from styrylcarbenoid species, are proposed by considering ratios of products in the control experiment.     

Gas-phase reactions of the bare Th2+ and U2+ ions with small alkanes, CH4, C2H6, and C3H8: experimental and theoretical study of elementary organoactinide chemistry

The gas-phase reactions of two dipositive actinide ions, Th(2+) and U(2+), with CH(4), C(2)H(6), and C(3)H(8) were studied by both experiment and theory. Fourier transform ion cyclotron resonance mass spectrometry was employed to study the bimolecular ion-molecule reactions; the potential energy profiles (PEPs) for the reactions, both observed and nonobserved, were computed by density functional theory (DFT). The experiments revealed that Th(2+) reacts with all three alkanes, including CH(4) to produce ThCH(2)(2+), whereas U(2+) reacts with C(2)H(6) and C(3)H(8), with different product distributions than for Th(2+). The comparative reactivities of Th(2+) and U(2+) toward CH(4) are well explained by the computed PEPs. The PEPs for the reactions with C(2)H(6) effectively rationalize the observed reaction products, ThC(2)H(2)(2+) and UC(2)H(4)(2+). For C(3)H(8) several reaction products were experimentally observed; these and additional potential reaction pathways were computed. The DFT results for the reactions with C(3)H(8) are consistent with the observed reactions and the different products observed for Th(2+) and U(2+); however, several exothermic products which emerge from energetically favorable PEPs were not experimentally observed. The comparison between experiment and theory reveals that DFT can effectively exclude unfavorable reaction pathways, due to energetic barriers and/or endothermic products, and can predict energetic differences in similar reaction pathways for different ions. However, and not surprisingly, a simple evaluation of the PEP features is insufficient to reliably exclude energetically favorable pathways. The computed PEPs, which all proceed by insertion, were used to evaluate the relationship between the energetics of the bare Th(2+) and U(2+) ions and the energies for C-H and C-C activation. It was found that the computed energetics for insertion are entirely consistent with the empirical model which relates insertion efficiency to the energy needed to promote the An(2+) ion from its ground state to a prepared divalent state with two non-5f valence electrons (6d(2)) suitable for bond formation in C-An(2+)-H and C-An(2+)-C activated intermediates.     

Lewis-acid-catalyzed rearrangement of arylvinylidenecyclopropanes: significant influence of substituents and electronic nature of aryl groups

Lewis-acid-catalyzed reactions of arylvinylidenecyclopropanes having three substituents at the corresponding cyclopropyl rings have been investigated thoroughly. The reaction products are highly dependent on the substituents at the corresponding cyclopropyl rings and the electronic nature of the aryl groups. For arylvinylidenecyclopropanes bearing two alkyl groups at the C-1 position (R1, R2, R3=aryl; R4=H; R5, R6=alkyl), naphthalene derivatives were formed in the presence of Lewis-acid Eu(OTf)3 in DCE at 40 degrees C. For arylvinylidenecyclopropanes in which R1, R2, R3=aryl and R4, R5=alkyl (syn/anti isomeric mixtures), the corresponding 6aH-benzo[c]fluorine derivatives were formed in the syn-configuration via a double intramolecular Friedel-Crafts reaction when all of the aryl groups do not have electron-withdrawing groups or the corresponding indene derivatives were obtained via an intramolecular Friedel-Crafts reaction as long as one electron-deficient aryl group was attached. For arylvinylidenecyclopropanes in which R1, R2, R3, R4=aryl and R5=alkyl or H, the corresponding indene derivatives were obtained exclusively via a sterically demanding intramolecular Friedel-Crafts reaction. Lewis-acid effects and mechanistic insights have been discussed on the basis of experimental investigations.     

Formal anti‐Carbopalladation Reactions of Non‐Activated Alkynes: Requirements,Mechanistic Insights,and Applications

Formal anti‐carbopalladation reactions of C? C triple bonds are uncommon, but highly useful transformations. Alkynes can be designed to give anti‐carbopalladation products. Prerequisite is the exclusion of other reaction pathways to provoke the cis–trans isomerization of the syn‐carbopalladation intermediate. Detailed mechanistic studies of this crucial step by experimental and computational means were performed. Application of an intramolecular version for the synthesis of oligocyclic compounds and substituted dibenzofurans is also described.     

BF3⋅OEt2‐Catalyzed Intermolecular Reactions of Vinylidenecyclopropanes with Bis(p‐alkoxyphenyl)methanols: A Novel Cationic 1,4‐Aryl‐Migration Process

BF₃?OEt₂‐catalyzed reactions of vinylidenecyclopropanes (VDCPs) 1 with bis(aryl)methanols 2 were thoroughly investigated. When VDCPs 1 reacted with electron‐rich bis(aryl)methanols 2 , diastereomeric rotamers of indene derivatives formed in excellent yields by a novel cationic 1,4‐aryl migration between two carbon atoms and the subsequent intramolecular Friedel–Crafts reaction pathways in the presence of BF₃?OEt₂ under mild conditions. As for electron‐deficient or less‐electron‐rich bis(aryl)methanols 2 , either trialkene products formed in good yields by direct deprotonation, or another type of indene derivative was produced by direct intramolecular Friedel–Crafts reaction, depending on the substituents on the cyclopropane of VDCPs. In addition, DFT calculations were carried out to explain the experimental results. Plausible mechanisms for all these transformations are proposed on the basis of the experimental and computational results.     

Reaction of phenyl radicals with propyne

The potential energy surface (PES) for the phenyl + propyne reaction, which might contribute to the growth of polycyclic aromatic hydrocarbons (PAHs) under a wide variety of reaction conditions, is described. The PES was characterized at the B3LYP-DFT/6-31G(d) and B3LYP-DFT/6-311+G(d,p) levels of theory. The energies of the entrance transition states, a direct hydrogen-transfer channel and two addition reactions leading to chemically activated C(9)H(9) intermediates, were also evaluated at the QCISD(T)/ 6-311G(d,p) and CCSD(T)/6-311G(d,p) levels of theory. An extensive set of unimolecular reactions was examined for these activated C(9)H(9)(dagger) intermediates, comprising 70 equilibrium structures and over 150 transition states, and product formation channels leading to substituted acetylenes and allenes such as PhCCH, PhCCCH(3), and PhCHCCH(2) were identified. The lowest energy pathway leads to indene, a prototype PAH molecule containing a five-membered ring. The title reaction thus is an example of possible direct formation of a PAH containing a five-membered ring, necessary to explain formation of nonplanar PAH structures, from an aromatic radical unit and an unsaturated hydrocarbon bearing an odd number of carbons. Extensive Supporting Information is available.     

Formation of aromatic structures from chain hydrocarbons in electrical discharges: absorption and fluorescence study of C11H9(+) and C11H9(•) isomers in neon matrices

A set of arenes (phenylacetylene, indene, and naphthalene cations and C(11)H(9)(+) isomers) was produced from 2,4-hexadiyne diluted in helium in a hot-cathode discharge source. The mass-selected ions were codeposited with neon at 6 K and investigated by electronic absorption spectroscopy. This reveals that fused-ring species are readily formed from an acyclic precursor in such a source. After photobleaching of matrices containing C(11)H(9)(+), neutral C(11)H(9)(?) radicals were also characterized. Assignment of the observed transitions to different m/z = 141 cationic and corresponding neutral isomers is given and supported by experiments using other precursors, fluorescence measurements, and time-dependent density functional and second-order approximate coupled cluster calculations.     

高温Shilov甲烷转化反应的机理和反应动力学研究

传统的Shilov反应是以PtCl2作为催化剂在水溶液中实现甲烷转化的,该反应的条件温和,在低至80°C时即可将甲烷中非常稳定的C–H键活化.然而,如果将反应温度提高达100°C以上,催化剂Pt(II)则非常容易发生歧化反应转化为Pt(0)或者Pt(IV),其中Pt(0)将会以沉淀的形式存在于反应溶液中.所以该反应只能在较低的温度进行, Shilov体系也只能得到较低的甲烷转化率,因此如何避免高温时催化剂因沉淀失活成为了提高反应转化率的研究重点.本文重点考察了高温条件下Shilov体系的反应机理和反应动力学,从而寻求提高催化体系活性和稳定性的途径.我们在特殊设计的金管反应器中进行了一系列的H/D置换实验,通过GC根据产物不同的分子量来分析检测.实验中,利用特殊设计的金管反应器可将反应压力增加到25.5 MPa,此时甲烷的溶解度与常温条件下(~60°C)相比可被提高1000倍以上,因此甲烷的转化率大大提高.在高温(~200°C)条件下的Shilov体系的水溶液中添加了CD3COOD, F3COOD, D2SO4, DCl和一系列阳离子为[1mim]+的离子液体来考察它们对催化剂沉淀的抑制作用,结果发现,在140°C时添加30%CD3COOD可在少量催化剂存在的条件下就能够明显促进H/D交换,与Shilov的结论吻合.这可能是由于CD3COO基团的螯合作用造成的,但将反应温度升到150°C时则不可避免的生成了Pt(0)沉淀.而F3COOD却在较多催化剂的条件下仍未表现出明显作用,可能是因为F较强的亲电子性使得F3COO基团的螯合作用变弱所致.在140°C时, D2SO4和DCl均能有效抑制Pt(0)沉淀的生成,尤其是DCl,在185°C反应24 h后仍能够稳定水溶液中的Pt基催化剂,但是在该条件下D2SO4却并没有作用.我们还发现, Cl–的浓度与沉淀的抑制直接相关,浓度越高对Pt基催化剂的稳定作用越强,但质子浓度的增加则对沉淀现象没有太大影响,我们推断原因是大量的Cl-能够在[PtCl6]2–的共同作用下将Pt(0)重新转化为了[PtCl6]2–.在140°C进行反应时,各类离子液体的添加能够使Pt(0)沉淀得到抑制,但是对H/D交换率却没有影响,可能是因为离子液体与Pt基催化剂螯合形成了Pt-离子液复合物而削弱了催化活性.在此基础上,我们特别考察了Cl–浓度对催化剂沉淀的影响,发现在200°C时将Cl-浓度提高到一定程度,就能够完全抑制Pt(0)的生成,但Pt基催化剂的活性也会被同时削弱.由于高压金管反应器的应用和高浓度Cl–的添加,使得甲烷的转化率达到90%以上,因此,我们设计了H/D同位素交换实验来考察反应的活性和选择性,从而针对高温Shilov体系的反应动力学进行研究.反应在200°C时进行,催化剂为K2PtCl4,反应介质为30% CD3COOD和DCl的水溶液,实验产物中检测到了CH3D, CH2D2, CHD3和CD4四种甲烷的多重氘代同位素体,说明了交换反应中有多个C–H键被活化.在此基础上,为了对甲烷活化过程进行全面描述,我们建立了涵盖所有连锁反应在内的综合反应网络,其中包含了H/D交换过程中涉及到的一系列平行的一级反应,基于实验数据通过阿伦尼乌斯方程计算得到了全部反应的频率因子、活化能和化学计量系数等反应动力学参数.结果证明,由于甲烷中所有的C–H键均相同,因此多重氘代产物的生成在甲烷转化过程中是不可避免的.其中,甲烷的单一氘代反应活化能为29.9 kcal/mol,双重氘代反应活化能为29.8 kcal/mol,两者十分相近,因此甲烷活化后的单一氘代产物的选择性最高不会超过50%.     

Thermal and photochemical oxidation of self-assembled monolayers on alumina particles exposed to nitrogen dioxide

Alumina is an important component of airborne dust particles as well as of building materials and soils found in the tropospheric boundary layer. While the uptake and reactions of oxides of nitrogen and their photochemistry on alumina have been reported in the past, little is known about the chemistry when organics are also present. Fourier transform infrared (FTIR) spectroscopy at ～23 °C was used to study reactions of NO(2) on γ-Al(2)O(3) particles that had been derivatized using 7-octenyltrichlorosilane to form a self-assembled monolayer (SAM). For comparison, the reactions with untreated γ-Al(2)O(3) were also studied. In both cases, the particles were exposed to water vapor prior to NO(2) to provide adsorbed water for reaction. As expected, surface-bound HONO, NO(2)(-), and NO(3)(-) were formed. Surprisingly, oxidation of the organic by surface-bound nitrogen oxides was observed in the dark, forming organo-nitrogen products identified as nitronates (R(2)C[double bond, length as m-dash]NO(2)(-)). Oxidation was more rapid under irradiation (λ > 290 nm) and formed organic nitrates and carbonyl compounds and/or peroxy nitrates in addition to the products observed in the dark. Mass spectrometry of the gas phase during irradiation revealed the production of NO, CO(2), and CO. These studies provide evidence for oxidation of organic compounds on particles and boundary layer surfaces that are exposed to air containing oxides of nitrogen, as well as new pathways for the formation of nitrogen-containing compounds on these surfaces.     

The formation of naphthalene, azulene, and fulvalene from cyclic C5 species in combustion: an ab initio/RRKM study of 9-H-fulvalenyl (C5H5-C5H4) radical rearrangements

Chemically accurate ab initio Gaussian-3-type calculations of the C(10)H(9) potential energy surface (PES) for rearrangements of the 9-H-fulvalenyl radical C(5)H(5)-C(5)H(4) have been performed to investigate the formation mechanisms of polycyclic aromatic hydrocarbons (PAHs) originated from the recombination of two cyclopentadienyl radicals (c-C(5)H(5)) as well as from the intermolecular addition of cyclopentadienyl to cyclopentadiene (c-C(5)H(6)) under combustion and pyrolytic conditions. Statistical theory calculations have been applied to obtain high-pressure-limit thermal rate constants, followed by solving kinetic equations to evaluate relative product yields. At the high-pressure limit, naphthalene, fulvalene, and azulene have been shown as the reaction products in rearrangements of the 9-H-fulvalenyl radical, with relative yields depending on temperature. At low temperatures (T < 1000 K), naphthalene is predicted to be the major product (>50%), whereas at higher temperatures the naphthalene yield rapidly decreases and the formation of fulvalene becomes dominant. At T > 1500 K, naphthalene and azulene are only minor products accounting for less than 10% of the total yield. The reactions involving cyclopentadienyl radicals and cyclopentadiene have thus been shown to give only a small contribution to the naphthalene production on the C(10)H(9) PES at medium and high combustion temperatures. The high yields of fulvalene at these conditions indicate that cyclopentadienyl radical and cyclopentadiene more likely represent significant sources of cyclopentafused PAHs, which are possible fullerene precursors. Our results agree well with a low-temperature cyclopentadiene pyrolysis data, where naphthalene has been identified as the major reaction product together with indene. Azulene has been found to be only a minor product in 9-H-fulvalenyl radical rearrangements, with branching ratios of less than 5% at all studied temperatures. The production of naphthalene at low combustion temperatures (T < 1000 K) is governed by the spiran mechanism originally suggested by Melius et al. At higher temperatures, the alternative C-C bond scission route, which proceeds via the formation of the cis-4-phenylbutadienyl radical, is competitive with the spiran pathway. The contributions of the previously suggested methylene walk pathway to the production of naphthalene have been calculated to be negligible at all studied temperatures.