Q27E - Organic Chemistry (Mcmurry)

Question

Predict the products for the reactions in Problem 8-26 if each were run in DMSO with water. Show the complete mechanism including appropriate regiochemistry and stereochemistry.

Step-by-Step Solution

Answer

(a) Therefore, the overall reaction is anti-addition. The halohydrin process is a regioselective process (i.e., one product is favored over the other product). The OH group attacks at the more substituted carbon atom. Therefore, the product of the reaction is as follows.  

(b) The overall reaction is anti-addition. Therefore, product of the reaction is as follows.

(c) The overall reaction is anti-addition. Therefore, a product of the reaction is as follows.

(a) First electrons of alkene interact with Br2 molecule

In this reaction first electrons of alkene interact with the Br2 molecule to form the cyclic bromonium ion along with the formation of the bromide ion.

If the reaction mixture is treated with DMSO with water, then the water molecule opens the bromonium ion from the opposite side at a more substituted carbon atom.

Here, the water molecule acts as a base and deprotonates the oxonium ion to form bromohydrin (1R, 2R)-2-Bromo-1,2-dimethylcyclohexanol.

Therefore, the overall reaction is anti-addition. The halohydrin process is a regioselective process (i.e., one product is favored over the other product). The OH group attacks the more substituted carbon atom. Therefore, the product of the reaction is as follows.

(b) First electrons of alkene interact with Cl2 molecule

 In this reaction first electrons of alkene interact with the Cl2 molecule to form the cyclic chloronium ion intermediate along with the formation of chloride ion.

If the reaction mixture is treated with DMSO with water, then the water molecule opens the chloronium ion intermediate at a more substituted carbon atom from the opposite side. Thus, the chloronium ion is above the plane, hence water molecules open the cyclic chloronium ion from below the plane.

The water molecule acts as a base

Here, the water molecule acts as a base and deprotonates the oxonium ion to form chlorohydrin (S)-2-chloro-1-phenylethanol.

Therefore, the overall reaction is anti-addition.

Therefore, the product of the reaction is as follows.

(c) First electrons of alkene interact with Cl2 molecule

In this reaction first electrons of alkene interact with the Cl2 molecule to form the cyclic chloronium ion intermediate along with the formation of chloride ion.

If the reaction mixture is treated with DMSO with water, then the water molecule opens the chloronium ion intermediate at a more substituted carbon atom from the opposite side.

Here, the water molecule acts as a base and deprotonates the oxonium ion to form chlorohydrin (2R, 3R)-3-chlorobutan-2-ol.

Therefore, the overall reaction is anti-addition

Therefore, product of the reaction is as follows.