Alevel化学：烯烃部分知识点梳理总结

2017-10-30 1898浏览

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The homologous series of alkenes has the general formula CnH2n. Alkenes are unsaturated hydrocarbons with one carbon-carbon double bond consisting of a σbond and a πbond.

烯烃同系物通式为：CnH2n。烯烃是具有一个碳碳双键的不饱和碳氢化合物，碳碳双键由一个σ键和一个 π键组成。

Ethene is a planar molecule, other alkenes are planar of the double bond and the four adjacent atom. Many alkenes have cis-trans isomers which arise because rotation about the double bond is prevented.

乙烯是一个平面分子。烯烃的碳碳双键以及与其相连的四个原子均处在同一平面上，由于碳碳双键不可扭转，一些烯烃存在顺反异构体。

Alkenes are more reactive than alkanes because they contain aπbond. The characteristic reaction of the alkene functional group is addition, which occurs across the πbond. For example ethene produces ethane with hydrogen over a nickel catalyst; 1,2-dibromoethane with bromine at room temperature; chloroethane with hydrogen chloride at room temperature; ethanol with steam in the prescence of H3PO4.

由于烯烃中存在一个π键，烯烃相对于烷烃来说较活泼。由于碳碳双键官能团的存在，烯烃可以通过π键发生加成反应。例如，乙烯和氢气在镍的催化作用下可以生成乙烷，在室温下可以与溴反应生成1.2-二溴乙烷，在室温下雨氯化氢反应生成氯乙烷，在H3PO4存在的条件下与水蒸汽生成乙醇。

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The mechanism of the reaction of bromine with ethene is electrophilic addition. Electrophiles accept a pair of electrons from an electron-rich atom or centre, in this case theπbond. A carbocation intermediate is formed after the addition of the first bromine atom. This rapidly reacts with a bromide ion to form 1,2-dibromoethane.

乙烯与溴的反应机理为亲电加成.溴受外界影响，其一端带微正电荷，形成亲电试剂，亲电试剂容易与富电子原子结合，形成π配位化合物，双键中的碳在接受了第一个溴原子的进攻之后，形成了碳正离子，碳正离子的形成促使其很快与另一个溴原子结合，形成1.2-二溴乙烷。

Alkenes produce many useful polymers by addition polymerisation. For example, poly(ethene) from CH2=CH2, poly(propene) from CH3CH=CH2, poly(chloroethene) from CH2=CHCl and poly(tetrafluoroethene) from CF2=CF2.

烯烃通过加成反应可以生成许多高分子材料。例如，CH2=CH2可以生成聚乙烯，CH3CH=CH2可以生成聚丙烯，CH2=CHCl可以生成聚氯乙烯，CF2=CF2可以生成聚四氟乙烯。

The disposal of polymers is difficult as they are chemically inert and non-biodegradable. When burnt, they may produce toxic products such as hydrogen chloride from PVC(poly(chloroethene)). Whilst much manufacturing wast plastic is recycled, the costs of collecting and sorting most domestic plastic are too high to make recycling worthwhile. Use of the energy released on combustion (for heating buildings) is a better option for domestic waste, but treatment of flue gases is required to remove toxic pollutants. A third option is feedstock recycling where the polymers are separated and used as feedstock to make new polymers.

因为高分子材料属于化学惰性物质，并且不能够生物降解，因此，对于高分子物质的处理相对困难。如聚氯乙烯在焚烧情况下可以产生氯化氢有毒气体。

一般有以下几种方法：第一，一些工业废旧塑料可以回收利用，但是其回收利用的造价是相当高的；第二，利用一些本土废旧物的燃烧能量来给建筑物供热，但对其烟道气中的毒气要做有效处理；第三，将一些高分子废弃物分类，作为新的高分子材料给料使用。

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