HELPPP! Chemistry question! Watch

Luminique
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PLEASE HELP!!

Ok so I was doing this chemistry past paper. But i just cannot seem to understand this one question.
It is question 4bii on the paper below:

PAPER:

http://www.swanwickhall.derbyshire.s...W-QP-JAN09.PDF

MARKSCHEME:

http://www.swanwickhall.derbyshire.s...W-MS-JAN09.PDF

I would really appreciate it if someone could explain this to me!! I've looked at the markscheme but just don't understand why that is the answer

Thank you!
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charco
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(Original post by Luminique)
PLEASE HELP!!

Ok so I was doing this chemistry past paper. But i just cannot seem to understand this one question.
It is question 4bii on the paper below:

PAPER:

http://www.swanwickhall.derbyshire.s...W-QP-JAN09.PDF

MARKSCHEME:

http://www.swanwickhall.derbyshire.s...W-MS-JAN09.PDF

I would really appreciate it if someone could explain this to me!! I've looked at the markscheme but just don't understand why that is the answer

Thank you!
This is dehydrohalogenation, where the halogen atom is removed as well as a hydrogen from the adjacent carbon atom.

There are two possible hydrogen atoms that could be removed giving the double bond at either the 1-position or at the 2-position (molecule B)
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gingerbreadman85
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(Original post by charco)
This is dehydrohalogenation, where the halogen atom is removed as well as a hydrogen from the adjacent carbon atom.

There are two possible hydrogen atoms that could be removed giving the double bond at either the 1-position or at the 2-position (molecule B)
Indeed. The mechanism involves the base (usually KOH or NaOH for A-level examples) removing a hydrogen from a beta-carbon (a carbon next to the carbon the halide is attached to).

There are 3 different beta carbons in the structure, due to the symmetry of the molecule two will give the same product, 3-methylpent-2-ene (structure B) whereas the methyl group will instead give 2-ethybut-1-ene.
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charco
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(Original post by gingerbreadman85)
Indeed. The mechanism involves the base (usually KOH or NaOH for A-level examples) removing a hydrogen from a beta-carbon (a carbon next to the carbon the halide is attached to).

There are 3 different beta carbons in the structure, due to the symmetry of the molecule two will give the same product, 3-methylpent-2-ene (structure B) whereas the methyl group will instead give 2-ethybut-1-ene.
You have the alpha carbon incorrectly defined. The carbon attached to the carbon under consideration is the alpha carbon.

In this case the alpha carbons are those attached to the carbon that holds the halogen atom ...
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