BRAINCAKEAsymmetrical Alkenes
An asymmetrical (unsymmetrical) alkene has different groups on the two carbons of the C=C, such as propene, CH3CH=CH2. When it reacts with HBr, the H can add to either carbon, so two products are possible: a major product and a minor product.
The product depends on which carbocation forms in step 1:
• H adds to carbon 1: the positive charge is on carbon 2, which is bonded to two other carbons. This is a secondary carbocation, CH3CH+CH3. Br– then gives 2-bromopropane.
• H adds to carbon 2: the positive charge is on carbon 1, bonded to only one other carbon. This is a primary carbocation, CH3CH2CH2+, which gives 1-bromopropane.
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Key terms in this lesson
- carbocation
- A positively charged carbon atom formed as a reactive intermediate when a bond breaks heterolytically.
More in Alkenes
- Electrophiles
- Electrophilic Addition
- Reaction with Halogens
- Reaction with Hydrogen Halides
- Reaction of Alkenes with Halogens
- Reaction with COncnetrated Sulfuric Acid
- Asymmetrical Alkenes
- Reaction with Water
All 23 lessons in Alkenes · All AQA AS-level Chemistry topics