Acenaphthylene mechanism

Formation of the Two Isomeric Dimers of Acenaphthylene Mechanism of Dimerizationfrom the Sj and T, States of ACN Dimerization in the Presence of an Electron Acceptor or Electron Donor Dimerization of Substituted ACN Photochemical Dimerization in Organized and... 

Kig. 10.. Mechanism of carbonisation of acenaphthylene [100]. 1, acenaphthylene 11, polyaccnaphthylene 111, biaccnaphthylidcnc IV, fluorocyclcnc V, dinaphthyicncbutadienc VI, decacyclcnc Vll, zethrcnc. Reprinted from [100] courtesy of Marcel Dekkcr Inc. 

Of the three cases of the ElcB mechanism, the one most difficult to distinguish from E2 is (ElcB)i. One way to make this distinction is to study the effect of a change in leaving group. This was done in the case of the three acenaphthylenes (12), where it was found that (1) the three rates were fairly similar, the largest being only about four times that of the smallest, and (2) in... 

The symbols A, (A - A)s, and Aa refer to acenaphthylene monomer, its singlet excimer, and its stable dimer(s), respectively. Experimental support for the singlet excimer mechanism [(10.27b)-(10.27d)] has been provided by Chu and Kearns,<47) who have shown that the cis (but not the trans) dimer in EPA (300-195°K) gives a broad fluorescence emission due to a singlet excimer. This excited state was also demonstrated to lead to dimer dissociation. 

It has been possible to employ the heavy-atom solvent effect in determining the rate constants for the various intercombinational nonradiative transitions in acenaphthylene and 5,6-dichIoroacenaphthylene.<436,c,rate constants, which are not accessible in light-atom solvents due to the complexity of the mechanism and the low efficiency of intersystem crossing from the first excited singlet to the first excited triplet, can be readily evaluated under the influence of heavy-atom perturbation. 

The following simplified mechanism is consistent with all of the kinetic data, where A = 5,6-dichloroacenaphthylene or acenaphthylene ... 

A2 is the dimer, HA is ethyl iodide, and Q is ferrocene. This mechanism is essentially the same as that proposed for the dimerization of acenaphthylene. The steps involving possible singlet excimer formation and singlet dimerization have been excluded since they are at best relatively unimportant processes in heavy-atom solvents. Using the steady-state approximation, we can... 

Bromine-atom atomic resonance absorption spectrometry (ARAS) has been applied to measure the thermal decomposition rate constants of CF3Br in Kr over the temperature range 1222-1624 K. The results were found to be consistent with recently published theory. The formation of cyclopent[a]indene and acenaphthylene from alkyl esters of biphenyl-mono- and -di-carboxylic acids has been observed in flash vacuum pyrolyses at 1000-1100 °C. The kinetics and mechanisms of free-radical generation in the ternary system containing styrene epoxide, / -TsOH, and i-PrOH have been examined in both the presence and absence of O2. ... 

PAHs photooxidized by the type II singlet oxygen mediated mechanism include acenaphthylene, whose oxidized products and yields are shown in Fig. 10.29B (Barbas et al., 1994), phenanthrene (Barbas et al., 1996), anthracene (Dabestini et al., 1995), and tetracene (Dabestini et al., 1996). An additional photochemical process, the formation of photodimers, is also observed for acenaphthylene, anthracene, and tetracene. 

FIGURE 10.29 Typical photoproducts observed (A) in the irradiation (A = 300 nm) in air of naphthalene and 1-methylnaphthalene adsorbed on silica and formed by a Type I electron transfer (superoxide) mechanism (Barbas et al., 1993) and (B) in the irradiation in air of acenaphthylene (A = 350 nm) adsorbed on silica formed by a Type II singlet oxygen mechanism (Barbas et al., 1994) (adapted from Dabestani, 1997). 

Indene does not photodimerize unless sensitized,259 whereas acenaphthylene, 16, does so when irradiated directly.280-261 Although it is believed that this reaction involves triplets, the mechanism(s) must be somewhat unusual since the stereochemistry is controlled by the reaction solvent. 

Athene —r alcohol The reagent prepared from SnCla (1 equiv.) and NaBH (4 equiv.) in THF reacts with olefins to afford anti-Markownikoff alcohols after aqueous work-up. Examples include 2-phenylpropane-l-ol (58%) from a-methyl-styrene, isopinocampheol (40%) from a-pinene, cw-myrtanol (43%) from / -pinene, 1,2-diphenylethanol (53%) from frans-stilbene, and 1-hydroxy-acenaphthene (60%, together with acenapthene, 15%) from acenaphthylene. The reaction with dienes such as limonene and 1,5-cycIooctadiene gave complicated results. The mechanism of this hydroxylation is uncertain. 

The principal difference between considerations of fluotescenre behaviour of acenaphthylene polymers VI and those of the photophysical characteristics of vinylaro-matic polymers is that whilst the latter sterns may form excimers throu interactions between nearest-neighbour chromophores on the polymer chain, steric restrmnts preclude such a mechanism in polymers of acenaphthylene It has been suggested that the dominant mechanism for excimer formation in acenaphthylene derived systems involves interactions between next to nearest nei bours. Such a proposal has been validated for copolymers of acenaphthylene with methyl methacrylate and methyl acrylate and is reinforced by the observation of excimer emission in alternating copolymers incorporating acenaphthylene chromophores in steady state excitation. 

The mechanism of the electron transfer-sensitised dimerisation of acenaphthylene (188) has been studied in considerable detail. Two dimers (189) and (190), formed from the radical cation of acenaphthylene, are obtained in addition to (191) and (192) which incorporate the TCNE sensitiser. Fumaroni-trile behaves in a similar fashion yielding the dimers (189) and (190) as well as cycloadducts. A study of the energetics of electron transfer in acenaphthylene charge transfer photochemistry has been carried out. ... 

PAHs may also volatilize from soil. Volatilization of acenaphthene, acenaphthylene, anthracene, fluorene, and phenanthrene (low molecular weight PAHs) from soil may be substantial (Coover and Sims 1987 Southworth 1979 Wild and Jones 1993). However, of 14 PAHs studied in two soils, volatilization was found to account for about 20% of the loss of 1 -methyinaphthalene and 30% of the loss of naphthalene volatilization was not an important loss mechanism for anthracene, phenanthrene, fluoranthene, pyrene, chrysene, benz[a]anthracene, benzo[b]fluoranthene, dibenz[a,h]anthracene, benzo[a]pyrene, and indeno[1,2,3-c,d]pyrene (Park et al. 1990). 

The acenaphthylene/C104 system has been studied by Kikuchi and Mitoguchi in acetic anhydride and acetonitrile92 93 and by Kikuchi and Matsuno in nitrobenzene94, 9S and in nitromethane95. The results are not conclusive with regard to the initiation mechanism, which is currently under investigation. 

The other reaction can be isolated by using air-saturated solutions or by adding cyclooctatetraene, without sensitisers it gives only iy/i-dimer. In the molten phase, this is the only reaction that has been observed . As to the mechanism of the two competing processes, it seems convenient to attribute the former to an excited triplet state of acenaphthylene, and the latter to the excited singlet state of a Tr-complex, that gives only syn adduct because of its initial geometry. 

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