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Bạn đang xem: Addition reactions of alkenes

Mechanism

Learning Objective

predict the products/specify the reagents for EAR of hydrohalic acids (HX) with symmetrical alkenes


Xem thêm: Quy Trình Lắp Đặt Thanh Cân Bằng Dòng Điện Tại Xưởng Đức Sanh

This section looks at the reaction of symmetrical alkenes (like ethene, but-2-ene or cyclohexene) with hydrogen halides such as hydrogen chloride & hydrogen bromide. Since these alkenes have identical groups attached khổng lồ each end of the carbon-carbon double bond, regioselectivity does not apply.


Addition to symmetrical alkenes

All alkenes undergo addition reactions with the hydrogen halides. A hydrogen atom joins lớn one of the carbon atoms originally in the double bond, và a halogen atom lớn the other.

For example, with ethene & hydrogen chloride, you get chloroethane:

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With but-2-ene you get 2-chlorobutane:

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What happens if you địa chỉ the hydrogen to lớn the carbon atom at the right-hand kết thúc of the double bond, and the chlorine to lớn the left-hand end? You would still have the same product. The chlorine would be on a carbon atom next to lớn the over of the chain - you would simply have drawn the molecule flipped over in space. That would be different of the alkene was unsymmetrical - that"s why we have to lớn look at them separately.