Question

draw the structure

Draw the major organic product formed in the following reaction.

Answer 1

Concepts and reason

${\bf{\alpha }}\,{\bf{ - }}\,{\bf{Hydrogen}}$ : The hydrogen bonded to the carbon(s) that is/are adjacent to a functional group, is termed as the ${\rm{\alpha - carbon}}$ , hydrogen atom bonded to such carbon atom is called as ${\rm{\alpha }}\,{\rm{ - }}\,{\rm{hydrogen}}$ . In case of aldehyde and ketones ${\rm{\alpha }}\,{\rm{ - }}\,{\rm{Hydrogen}}$ are acidic in nature, due to the partial positive charge created in carbonyl carbon, as result of polarization of the ${\rm{C = O}}$ .

Base catalysed bromination of ketones:

• The hydroxide ion present in the system will abstract the alpha hydrogen and forms an enolate ion.

• The attack of enolate ion on the bromine molecule to form monosubstituted bromine compound.

• In the presence of excess bromine the reaction continues until all the alpha hydrogen atoms are substituted by bromine.

Fundamentals

The abstraction of α – hydrogen from aldehyde or ketone under basic conditions undergoes the formation of intermediate called Enolates.

An example for the mechanism of base promoted halogenation is given by,

The mechanism for the first bromination of the given reactant is given by,

The mechanism for the second bromination of the compound is given by,

Thus the major product of the reaction is,

Ans:

The major product of the reaction is identified to be,

Answer 2

Concepts and reason

The concept used in this question is the alpha bromination of the ketone.

Initially, the mechanism for the reaction of $1 - \left( {{\rm{p}} - {\rm{tolyl}}} \right){\rm{propan}} - 1 - {\rm{one}}$ in presence of an excess of dibromine is explained based on the concept of base-catalyzed halogenation of ketones. Lastly, the major organic product for the reaction of $1 - \left( {{\rm{p}} - {\rm{tolyl}}} \right){\rm{propan}} - 1 - {\rm{one}}$ in presence of an excess of dibromine is determined.

Fundamentals

Base-catalyzed halogenation of ketone:

The halogenation of ketone or aldehyde occurs by the removal of alpha hydrogen to form the alpha halogenated product. The reaction proceeds as follow:

The reaction proceeds in the presence of acids or base. For example, the base-catalyzed bromination of ${\rm{propan}} - {\rm{2}} - {\rm{one}}$ proceeds as follows.

The reaction of $1 - \left( {{\rm{p}} - {\rm{tolyl}}} \right){\rm{propan}} - 1 - {\rm{one}}$ with bromine takes place in the presence of a base as shown below.

The major organic product for the bromination of $1 - \left( {{\rm{p}} - {\rm{tolyl}}} \right){\rm{propan}} - 1 - {\rm{one}}$ in presence of the base is as follows.

Ans:

The major product for the given reaction is shown below.