If we substitute n=2 it satisfies the Huckel’s rule – 4n+2π electron condition. Low molecular weight PAHs, with two to four aromatic hydrocarbon rings, are more potent as co-carcinogens during the promotional stage of cancer.

[26][27], PAHs can also be produced geologically when organic sediments are chemically transformed into fossil fuels such as oil and coal. However, not all double bonds are in conjugation. The resulting mutations may contribute to unregulated growth of vascular smooth muscle cells or to their migration to the inside of the artery, which are steps in plaque formation. [20] Three Clar structures with two sextets each are present in the four-ring chrysene structure: one having sextets in the first and third rings, one in the second and fourth rings, and one in the first and fourth rings. [11], Other PAHs that might seem to be planar, considering only the carbon skeleton, may be distorted by repulsion or steric hindrance between the hydrogen atoms in their periphery. Excessive closure of these channels after exposure to PAHs results in removing a cell from the normal growth-regulating signals imposed by its local community of cells, thus allowing initiated cancerous cells to replicate. Max Blumer (1975): "Curtisite, idrialite and pendletonite, polycyclic aromatic hydrocarbon minerals: Their composition and origin", Tetsuya Arinobu, Ryoshi Ishiwatari, Kunio Kaiho, and Marcos A. Lamolda (1999): "Spike of pyrosynthetic polycyclic aromatic hydrocarbons associated with an abrupt decrease in δ, United States Environmental Protection Agency, Agency for Toxic Substances and Disease Registry, International Agency for Research on Cancer, "Toxicity of Polycyclic Aromatic Hydrocarbons (PAHs): Health Effects Associated With PAH Exposure", "Need to Track Organic Nano-Particles Across the Universe? This molecule has 10 p-orbitals over which can overlap. See Wiktionary Terms of Use for details. Structures of PAHs have been analyzed using infrared spectroscopy.[101]. The large PAH form dianions as well. [32][51], In industrial countries, people who smoke tobacco products, or who are exposed to second-hand smoke, are among the most highly exposed groups; tobacco smoke contributes to 90% of indoor PAH levels in the homes of smokers. [citation needed], NASA's Spitzer Space Telescope includes instruments for obtaining both images and spectra of light emitted by PAHs associated with star formation. 4)The heat of hydrogenation calculation also show stabilisation in the molecule. Only one of the two rings has conjugation (alternate single and double bonds). The larger members, e.g. [67][70] In general estuarine sediments with a higher natural total organic carbon content (TOC) tend to accumulate PAHs due to high sorption capacity of organic matter. A polycyclic aromatic hydrocarbon (PAH) is a hydrocarbon—a chemical compound containing only carbon and hydrogen—that is composed of multiple aromatic rings.

Is naphthalene an aromatic or aliphatic compound? [16], The aromaticity varies for PAHs. Jan Cz. Change ), You are commenting using your Facebook account. [28][32][49] Developed countries with stricter air and water pollution controls, cleaner sources of cooking (i.e., gas and electricity vs. coal or biofuels), and prohibitions of public smoking tend to have lower levels of PAH exposure, while developing and undeveloped countries tend to have higher levels. Fill in your details below or click an icon to log in: You are commenting using your WordPress.com account. [60] Abiotic degradation in the atmosphere and the top layers of surface waters can produce nitrogenated, halogenated, hydroxylated, and oxygenated PAHs; some of these compounds can be more toxic, water-soluble, and mobile than their parent PAHs.[57][61][62]. - Quora. [32][31] As of 2004, industrial processes and the extraction and use of fossil fuels made up slightly more than one quarter of global PAH emissions, dominating outputs in industrial countries such as the United States. Moss IUPAC nomenclature for fused-ring systems. In the next post we will discuss some more PAHs. [89], Multiple epidemiological studies of people living in Europe, the United States, and China have linked in utero exposure to PAHs, through air pollution or parental occupational exposure, with poor fetal growth, reduced immune function, and poorer neurological development, including lower IQ. Larger PAHs are generally insoluble in water, although some smaller PAHs are soluble. [86] A leading hypothesis is that PAHs may activate the cytochrome enzyme CYP1B1 in vascular smooth muscle cells. [28][32] Geographically, major roadways are thus sources of PAHs, which may distribute in the atmosphere or deposit nearby. [56][66][67] Consequently, the concentrations of pollutants in estuaries tends to decrease at the river mouth. [81] Such mutations, if they are not repaired, can transform genes encoding for normal cell signaling proteins into cancer-causing oncogenes. Takuya Echigo, Mitsuyoshi Kimata, and Teruyuki Maruoka (2007): "Crystal-chemical and carbon-isotopic characteristics of karpatite (C. František Mikeš, Geraldine Boshart, and Emanuel Gil-Av (1976): "Resolution of optical isomers by high-performance liquid chromatography, using coated and bonded chiral charge-transfer complexing agents as stationary phases". However, the overall distribution also suggested that the PAHs in London soils had undergone weathering and been modified by a variety of pre-and post-depositional processes such as volatilization and microbial biodegradation. All the above points clearly indicate that naphthalene is an aromatic entity too.


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