Martin Sarobe

Thermal generation and (inter)conversion of (multi) cyclopenta-fused polycyclic aromatic hydrocarbons

FVT of I, 1 -dichloro- and/or 1 -chloroethenyl substituted PAHs gives access to the CP-PAHs pyracylene (l), cyclopenta(cd)pyrene (12) and benz(ghi)fluoranthene (13), cyclopent(hi)aceanthrylene (18) and cyclopent(hi)acephenanthrylene (19), and the novel cyclopenta(cd)fluoranthene (22) and isomeric cyclopent(fg)- (25a), cyclopent(ik)- (25b) and cyclopent(rnn)acepyrylene (25c), respectively. The propensity of CP-PAHs to interconvert under high temperature FVT conditions is illustrated. Possible mechanisms, such as ring-contractionhing-expansion via 1,2-H and 1,2-C shifts, are discussed.

Redox properties of non-alternant cyclopenta-fused polycyclic aromatic hydrocarbons: The effect of peripheral pentagon annelation

The redox properties of 23 alternant PAH and non-alternant mono- and bis-CP-PAH that contain annelated peripheral pentagons were determined using cyclic voltammetry. The results show that peripheral cyclopenta-fusion markedly enhances their electron affinity. Unexpectedly for the non-alternant PAH, a good linear correlation between the first reduction potential [E1/2(0/−1) V vs. SCE] and their standard Huckel LUMO energy (−eLUMO/β) is found. This indicates that the peripheral pentagons perturb the LUMO of the original alternant PAH core in a systematic fashion. A survey of the reduction behaviour of the mono- and bis-CP-PAH reveals that upon reduction the effect of the cyclopenta-moiety on the remainder of the molecule becomes negligible. Evidence for the formation of 6π-electron cyclopentadienide sub-structures is obtained, i.e. localization of the added electrons in the peripheral pentagons occurs.

Cyclopenta[cd]fluoranthene: Acefluoranthylene

Cyclopenta[cd]fluoranthene (1, acefluoranthylene) is obtained by Flash Vacuum Thermolysis of 3(1-chloroethenyl)fluorlanthene (4). The electronic properties (cyclic voltammetry , UV/Vis and fluorescence) of 1 are markedly affected by cyclopenta-fusion.

Thermolysis of benzo[c]phenanthrene: Conversion of an alternant C18H12 PAH into Non-alternant C18H10 PAHs

Abstract The product composition of the pyrolysates obtained upon thermolysis of the alternant C18H12 PAH benzo[c]phenanthrene (1) is markedly pressure dependent. At 0.1–0.5 Torr (N2 carrier gas, 1050–1150 °C) 1 is converted into the non-alternant C18H10 PAHs cyclopenta[cd]pyrene (4) and benzo[ghi]fluoranthene (5) which have been identified as abundant combustion effluents and are associated with fullerene formation.

Flash vacuum thermolysis of acenaphtho[1,2-a]acenaphthylene, fluoranthene, benzo[k]- and benzo[j]fluoranthene - Homolytic scission of carbon-carbon single bonds of internally fused cyclopenta moieties at T >= 1100 degrees C

Flash vacuum thermolysis (FVT, 1000 °C ≥ T ≥ 1200 °C) of acenaphtho[1,2-a]acenaphthylene (3, C22H12) gave the C22H12 cyclopenta-fused polycyclic aromatic hydrocarbon (CP-PAH) acenaphtho[1,2-e]acenaphthylene (4), cyclopenta[cd]perylene (5) and cyclopenta[def]benzo[hi]chrysene (6). Whereas the formation of 4 is explained by a ring contraction/ring expansion rearrangement of 3, the identification of 5 and 6 suggests that 3 also undergoes homolytic scission of a five-membered rings Carbon-Carbon single bond furnishing the transient diradical intermediate 7. Ring closure of 7to form 8 after rotation around the Carbon-Carbon single bond of the intact five-membered ring followed by hydrogen shifts will give 6. The latter can rearrange subsequently into 5by ring contraction/ring expansion. The structural assignment of 4 and 5 was supported by independent FVT of 6,12-bis(1-chloroethenyl)chrysene (14) and 3-(1-chloroethenyl)perylene (23), respectively. FVT of 14 (900–1200 °C) gave in a consecutive process 6,12-bis(ethynyl)chrysene (15), 9-ethynylbenz[j]acephenanthrylene (16) and bis(cyclopenta[hi,qr])chrysene (17). Although at T ≥ 900 °C 17 selectively rearranges into 4 by ring contraction/ring expansion, at 1200 °C the latter is converted into 5 presumably via a diradical intermediate obtained by homolytic scission of a single Carbon-Carbon bond of a five-membered ring. FVT of 23 gave in situ 3-ethynylperylene (25), which at 1000 °C is nearly quantitatively converted into 5. The propensity of internal cyclopenta moieties to undergo homolytic scission of a five-membered ring′s Carbon-Carbon single bond was corroborated by independent FVT of benzo[k]- (11) and benzo[j]fluoranthene (12). Previously unknown thermal pathways to important (CP)-PAH combustion effluents are disclosed at T ≥ 1000 °C.

Identification of isomeric polycyclic aromatic hydrocarbons (PAH) in pyrolysates from ethynylated PAH by gas chromatography-Fourier infrared spectroscopy. Their relevance for the understanding of PAH rearrangement and interconversion processes during combustion

The utility of gas chromatography with infrared spectrometric detection (GC-IR) for the structural elucidation of pyrolysate constituents obtained by Flash Vacuum Pyrolysis (FVP; 900–1100°C, 10−2 Torr) of ethynylated Polycyclic Aromatic Hydrocarbons (E-PAH) is demonstrated. E-PAH are efficient precursors for ubiquitous and genotoxic C14H8, C16H10 and C20H12 cyclopenta-fused PAH (CP-PAH) combustion effluents. The formation of CP-PAH from E-PAH as well as CP-PAH rearrangements and/or interconversions are readily recognized. GC-IR being complementary to GC-MS enables the identification and structural assignment of previously undetected isomeric PAH, which are only present in trace-level amounts. The results are of interest for the elucidation of PAH build up processes and for the rationalization of the ubiquitous formation of a distinct set of PAH during combustion.

Flash vacuum thermolysis of 1,5-Bis-(1-chloroethenyl)anthracene. The thermal conversion of cyclopent[hi]aceanthrylene into cyclopent[hi]acephenanthrylene

Abstract Flash Vacuum Thermolysis of 1,5-bis-(1-chloroethenyl)anthracene (6) gives cyclopent[hi]-aceanthrylene (2) which at T≥9000 °C rearranges to cyclopent[hi]acephenanthrylene (1). This conversion occurs more readily than that of the monocyclopenta-fused aceanthrylene to acephenanthrylene.

The Shpol'skii fluorescence spectrum of cyclopenta[c,d]pyrene.

Abstract The high resolution Spholskii fluorescence spectrum of the non-alternant polycyclic aromatic hydrocarbon cyclopenta[c,d]pyrene (CPP, 1) in an n-hexane matrix at cryogenic temperature is reported. Two distinct narrow spectral lines at 378.0 and 379.6 nm representing two sites were found, whereas in n-octane no Spholskii effect was observed. In accordance with reported data on the fluorescence of CPP (1) these lines have to be assigned to anomalous S2-emission.

Externally-fused cyclopenta moieties in non-alternant CP-PAHs act as peri-substituents

Abstract The Hammett constants σ m for the externally fused cyclopenta moiety in the CP-PAHs 1 (1,8-CP), 2 (1,9-CP), 3 (1,10-CP) and 4 (3,5-CP) have been determined. The σ m values for these structurally different CP-PAHs are nearly identical. This gives evidence that the cyclopenta moiety acts as a peri -substituent with σ m =0.4±0.07.

MIGRATION OF REDUNDANT ETHYNYL SUBSTITUENTS ALONG POLYCYCLIC AROMATIC HYDROCARBON PERIPHERIES. CONSEQUENCES FOR POLYCYCLIC AROMATIC HYDROCARBON BUILD UP

Abstract The formation of cyclopenta[ cd ]pyrene ( 5 ) and benzo[ ghi ]fluoranthene ( 6 ) upon FVT of 3,9- bis ethylphenanthrene ( 1 ) and 8-ethynylfluoranthene ( 2 ), respectively, suggests that redundant ethynyl substituents, which cannot give five- and/or six-membered ring formation via ethynyl ethylidene carbene equilibration followed by carbene CH insertion, can migrate along the PAH periphery at high temperatures.