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question related to free radical mechanism

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ashwinkandel:
25 When heated with chlorine, the hydrocarbon 2,2-dimethylbutane undergoes free radical
substitution.
In a propagation step the free radical X• is formed.
CH3CH2C(CH3)2CH3 + Cl? ? X? + HCl

How many different forms of X• are possible?
A 1
B 2
C 3
D 4

can someone tell me the answers with reason and reacction plz.

ashwinkandel:
another question too..
27 Which isomer of C4H10O forms three alkenes on dehydration?
A butan-1-ol
B butan-2-ol
C 2-methylpropan-1-ol
D 2-methylpropan-2-ol

Deadly_king:

--- Quote from: ashwinkandel on October 04, 2010, 05:02:09 pm ---another question too..
27 Which isomer of C4H10O forms three alkenes on dehydration?
A butan-1-ol
B butan-2-ol
C 2-methylpropan-1-ol
D 2-methylpropan-2-ol

--- End quote ---

Butan-1-ol will form only one alkene since the OH group is found on the first carbon atom. Hence upon dehydration the OH group and an adjacent H atom will condense to form one mole of water to form an alkene.

Butan-2-ol will form 2 alkenes since it has equal chance of producing an alkene with the hydrogen atom from adjacent H atoms from both sides(Either the first carbon atom or the third one). Its OH group is situated on the second carbon atom.

2-methylpropan-1-ol has one OH group on the first carbon atom and two methyl groups on the neighbouring carbon atom. However, since it is a primary alcohol, dehydration will result in the formation of only one alkene since the carbon atom containing the OH group is attached to only one other carbon atom.

2-methyl-propan-2-ol is a secondary alcohol. If you draw its structural formula, you'll realize that any alkene formed will be the same one due to different possible orientations. Hence it will form only one type of alkene.

For me, all the four answers given are inappropriate. But if I had to choose one, it will be butan-2-ol since it can form the most alkenes possible (2).

NOTE : All primary alcohols are first eliminated since they can form only one type of alkene upon dehydration.

Though I can't find any other worth explanation  :-\

Deadly_king:

--- Quote from: ashwinkandel on October 04, 2010, 05:00:38 pm ---25 When heated with chlorine, the hydrocarbon 2,2-dimethylbutane undergoes free radical
substitution.
In a propagation step the free radical X• is formed.
CH3CH2C(CH3)2CH3 + Cl? ? X? + HCl

How many different forms of X• are possible?
A 1
B 2
C 3
D 4

can someone tell me the answers with reason and reacction plz.

--- End quote ---

I believe it is 4

Free radical substitution reaction may occur on each carbon atoms of the butane group. This makes a total of 3 types.

Then one type for the methyl groups, in both cases it will be the same radical. Hence it is taken as only one type.

Try draw its displayed formula. It might help you to understand better and don't forget about the different orientations  ;)

ashwinkandel:
this is the question from 2010 paper no 12. according to marking scheme the answer of question one which i asked is B and question two is C.

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