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Physical And Chemical Properties Of Polycyclic Aromatic Hydrocarbon
Jul 14, 2017

Polycyclic aromatic hydrocarbon are mostly colorless or pale yellow crystals, individual with dark, high melting point and boiling point, the vapor pressure is very small, mostly insoluble in water, soluble in benzene aromatic solvents, slightly soluble in other organic In the solvent, the octanol - water partition coefficient is relatively high. Polycyclic aromatic hydrocarbon have a large conjugate system, so the solution has a certain fluorescence. In general, with the increase in the molecular weight of polycyclic aromatic hydrocarbon, the melting point increases and the vapor pressure decreases. The color, fluorescence and solubility of PAHs are mainly related to the conjugation system of polycyclic aromatic hydrocarbon and the arrangement of molecular benzene rings.With the increase of p electron number and the enhancement of p electron delocalization, the color is enhanced and the fluorescence enhancement , The maximum absorption wavelength in the UV absorption spectrum is also shifted to the long wave direction. For the polycyclic aromatic hydrocarbon with linear polycyclic aromatic hydrocarbon, the number of benzene rings increases, the octanol-water partition coefficient increases, the polycyclic aromatic hydrocarbon with the same number of benzene rings, The more "cluster" octanol - the greater the water partition coefficient.

Polycyclic aromatic hydrocarbon are chemically stable, and when they react, they tend to retain their conjugated ring systems and generally act as an active form of the final carcinogen by electrophilic substitution to form a derivative. The basic unit is a benzene ring, but the chemical properties and benzene is not exactly the same. Divided into the following categories:

(1) Compounds having a fused polyphenylene structure

Such as triphenylene, dibenzo [e, i] pyrene, tetrabenzo [a, c, h, j] anthracene and the like, have similar chemical stability with benzene, indicating that the distribution of electrons in these PAHs is Similar to benzene. As shown in Figure 1:

⑵ were arranged in a row of polycyclic aromatic hydrocarbon

Such as anthracene, Ding province, E province, etc., than the chemical nature of benzene much more lively. Its reactive activity increases with the ring and stronger, the number of rings to reach seven of the G, the chemical nature of very lively, almost can not get pure. The polycyclic aromatic hydrocarbon (PAHs) are characterized by chemical reactions, which often occur in the relative carbon position (referred to as anthracene) in the middle of a benzene ring corresponding to anthracene. as shown in picture 2:

Such as phenanthrene, benzo [a] ac, cisato [2,3-a] anthracene, lucine, [2,3-a] lui, etc., the chemical activity is generally smaller than the corresponding linearly arranged isomers. In the addition reaction, usually in the middle of the equivalent of phenanthrene double bond position, that is, the Philippines 9,10 key (referred to as the Philippine bond) on. Π electrons are largely limited to the phenanthrene bond, so the chemical properties of the phenanthrene are very close to the olefinic bond. Angular polycyclic aromatic hydrocarbon containing more than four rings, in addition to the more lively in the Philippine bond, but also often contains a linear polycyclic aromatic hydrocarbon similar to the active - in the bit, such as benzo [a] onion 8,15 Bit. But the degree of lively than the corresponding linear isomer is low, basically with the increase in the number of rings as shown in Figure 3:

⑷ more complex structure of the fused ring hydrocarbons

Such as benzo [a] flowers, dibenzo [a, i] pyrene, etc., with a lively in the Philippines, but no lively alignment. Such polycyclic aromatic hydrocarbon in a lot of carcinogenicity, such as benzo [a] pyrene is the most carcinogenic polycyclic aromatic hydrocarbon.

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