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Question
Which of the following reactions will yield 2,2-dibromopropane as the major product?
Which of the following reactions will yield 2,2-dibromopropane as the major product?
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Solution
The correct option is B CH3−C≡CH+2HBr→
When two molecules of HX (HCl, HBr or HI) add to the alkynes they form geminal dihalides. In geminal dihalides two halogen atoms are attached to the same carbon atom.
Addition of HX on alkynes obeys Markovnikov's rule.
Markovnikov's rule : Negative part of the addendum (adding molecule) gets attached to that doubly bonded C which posses lesser number of hydrogen atoms.
Reaction of propyne with of HBr to form 2, 2-Dibromopropane can be written as:
CH3−C≡CH+HBr→CH3−C(Br)=CH2
CH3−C(Br)=CH2+HBr→CH3−C(Br)2−CH3
The reaction follows Markownikoff's rule.
Reaction (a) gives 2-Bromopropane by Markovnikov's rule.
Reaction (c) gives 2,2 -Dibromopropane by Markovnikov's rule.
Reaction (d) gives 1,1- Dibromoethane by Markovnikov's rule.
Thus, option (c) is the correct answer.
When two molecules of HX (HCl, HBr or HI) add to the alkynes they form geminal dihalides. In geminal dihalides two halogen atoms are attached to the same carbon atom.
Addition of HX on alkynes obeys Markovnikov's rule.
Markovnikov's rule : Negative part of the addendum (adding molecule) gets attached to that doubly bonded C which posses lesser number of hydrogen atoms.
CH3−C≡CH+HBr→CH3−C(Br)=CH2
CH3−C(Br)=CH2+HBr→CH3−C(Br)2−CH3
The reaction follows Markownikoff's rule.
Reaction (a) gives 2-Bromopropane by Markovnikov's rule.
Reaction (c) gives 2,2 -Dibromopropane by Markovnikov's rule.
Reaction (d) gives 1,1- Dibromoethane by Markovnikov's rule.
Thus, option (c) is the correct answer.
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