Q27E - Organic Chemistry (Mcmurry)

Question

Each of the following substances can be prepared by a nucleophilic

addition reaction between an aldehyde or ketone and a nucleophile.

Identify the reactants from which each was prepared. If the substance is an acetal, identify the carbonyl compound and the alcohol; if it is animine, identify the carbonyl compound and the amine; and so forth.

Step-by-Step Solution

Answer

(a)

(b)

(c)

(d)

Step 1: Nucleophilic addition reaction

Nucleophilic addition reaction is one of the particular reactions shown by the “carbonyl compound”: aldehyde and ketone.

In the nucleophilic addition reaction, attack of both nucleophile and electrophile occur, but the attack of the nucleophile on the carbonyl carbon (planar spececis)  is the slow step; thus, it is the rate-determining step.

 

Step 2: Reactant used for the formation of acetal

The given compound (a) is cyclic acetal prepared from a diol reacting with an aldehyde.

 

To reactant aldehyde used is find out by replacing the two -OR group with =O, which comes out as acetaldehyde, and the remaining form is propane-1,3-diol.

 

The reactants used to form the acetal are shown as follows:

                                               Formation of acetal

Step 3: Reactant used for the formation of imine

The given compound (b) is imine as it contains a carbon-nitrogen double bond(C=N); the carbon, which is the part of C=N, comes from the ketone, and the nitrogen comes from a primary amine.

The ketone and the primary amine used can be found by breaking the double bond between the nitrogen and carbon formed in imine; thus, the ketone used is a propane-2-one, and the primary amine used is phenylalanine 

 

The reactants used to form the imineare shown as follows:

 

                                        Formation of imine

Step 4: Reactant used for the formation of enamine

The given compound (c) is enamine as it contains a carbon-nitrogen single bond(C-N); the carbon, which is the part of C-N, comes from the ketone, and the nitrogen comes from a secondary amine.

The ketone and primary amine can be found by breaking the single bond between the nitrogen and carbon formed in enamine; thus, the ketone used is cyclopentanone, and the secondary amine usedis pyrrolidine.

 

The reactants used to form the enamine are shown as follows:

                                                  Formation of enamine

Step 5: Reactant used for the formation of 2-methyl-1-p-tolylpropan-1-ol

The given compound (d) is 2-methyl-1-p-tolylpropan-1-ol which is formed by two methods as follows:

• One of the methods is to reduce the ketone 2-methyl-1-p-tolylpropan-1-one with the help of a reducing agent, sodium borohydride $\left({\text{NaBH}}_{\text{4}}\right)$,followed by acidic hydrolysis.
• Another method is the addition of Grignard reagent to the aldehyde ${\left({\text{CH}}_{\text{3}}\right)}_{\text{2}}\text{CHCHO}$ followed by acidic hydrolysis.

 

The reactants used to form the 2-methyl-1-p-tolylpropan-1-ol are shown as follows:

                                             Formation of 2-methyl-1-p-tolylpropan-1-ol