Chemistry Hydrocarbons MDCAT 2018
PMDC Verified Question 41 of 65
Bromination of alkene is shown in the following reaction. (Ethene + \( \text{Br}_2 \rightarrow \) 1,2-dibromoethane). This reaction is used for:
A
Identification of primary and secondary alcohols
B
Detection of aldehydes
C
Detection of ketones
D
Detection of double bond
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option D: Detection of double bond
Concept:

The addition of molecular bromine (\( \text{Br}_2 \)) across a carbon-carbon double bond is a classic diagnostic chemical test.

Solution:

  • A solution of bromine in carbon tetrachloride (or water) has a distinct reddish-brown color.


  • When reacted with an alkene, the bromine is rapidly consumed through an electrophilic addition reaction, forming a colorless vicinal dibromide (e.g., 1,2-dibromoethane).


  • The immediate disappearance (decolorization) of the reddish-brown color provides visual confirmation of unsaturation. Therefore, it is used for the detection of a double bond.


Why other options are incorrect:

  • Alcohols, aldehydes, and ketones do not readily undergo addition reactions with bromine to decolorize it under these mild conditions.

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