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Hydrocarbons là các hợp chất bao gồm carbon và hydro một mình. Họ có thể được phân loại thành hai nhóm chính. 1 hydrocacbon thơm, có chứa hệ thống vòng với các điện tử delocalised, ví dụ như Benzene. 2 phi hydrocacbon thơm, không chứa một hệ thống vòng. Bao gồm ở đây là alkan, hoàn toàn bão hòa hydrocacbon, alkene, có chứa một hoặc nhiều liên kết đôi, và alkynes, có chứa một hay nhiều liên kết ba. Một số ví dụ về các loại khác nhau của hydrocarbon được đưa ra trong hình 9.1. Các hợp chất Nonaromatic. | CHAPTER 9 Polycyclic aromatic hydrocarbons 9.1 Background Hydrocarbons are compounds composed of carbon and hydrogen alone. They may be classified into two main groups. 1 Aromatic hydrocarbons which contain ring systems with delocalised electrons e.g. benzene. 2 Non-aromatic hydrocarbons which do not contain such a ring system. Included here are alkanes which are fully saturated hydrocarbons alkenes which contain one or more double bonds and alkynes which contain one or more triple bonds. Some examples of different types of hydrocarbons are given in Figure 9.1. Nonaromatic compounds without a ring structure are termed aliphatic and those with a ring structure e.g. cyclohexane are termed alicyclic . Aromatic hydrocarbons often consist of several fused rings as in the case of benzo a pyrene. Both classes of hydrocarbon occur naturally notably in oil and coal deposits. Aromatic compounds are also products of incomplete combustion of organic compounds and they are released into the environment both by the activities of man and by certain natural events e.g. forest fires and volcanic activity. Aromatic hydrocarbons the subject of this chapter are of particular concern because of the carcinogenic and or mutagenic properties of some of them. Inevitably there 2001 C. H. Walker 166 Major organic pollutants Non-aromatic H H H . i i i . H-C-C-C-H .1. .1. .1. H H H Propane H H V H H H H Cyclohexane Aromatic Naphthalene Benzo a pyrene 4 3 Fluoranthene Figure 9.1 Structures of some hydrocarbons. are questions about possible harmful effects on ecosystems that are exposed to high levels of them. Non-aromatic hydrocarbons are usually of low toxicity have not received much attention in ecotoxicology and will not be discussed further in the present text. It should however be remembered that crude oil consists mainly of alkanes and large releases into the sea because of the wreckage of oil tankers have caused the death of many sea birds and other marine organisms as a result of their
