Q.57 - Organic Chemistry

Question

Draw all of the substitution and elimination products formed from the given alkyl halide with each reagent: (a) ${\mathbf{\text{CH}}}_{\mathbf{3}}\mathbf{\text{OH}}$; (b) KOH. Indicatethe stereochemistry around the stereogenic centers present in theproducts, as well as the mechanism by which each product is formed.

Step-by-Step Solution

Answer

The substitution and the eliminations products formed from the given compound are as follows:

Anti-periplanar orientations

To undergo elimination reactions, the protons and the leaving group must be in a trans-position with each other to give an elimination product.

Types of base/nucleophile use

• Weak bases and weak nucleophiles such as methanol promote a mixture of both ${\text{S}}_{\text{N}}\text{1}$ and E1 reactions. 

 

• Strong bases and strong nucleophiles such as hydroxides promote a mixture of both ${\text{S}}_{\text{N}}\text{2}$ and E2 reactions. 

Types of substrates used

Tertiary halides undergo a  ${\text{S}}_{\text{N}}\text{1}$ and E1 reaction respectively when a weak nucleophile and a weak base are used. 

Secondary halides undergo a ${\text{S}}_{\text{N}}\text{1}$  and E1 reaction respectively when a weak nucleophile and a weak base are used. Secondary halides undergo a  ${\text{S}}_{\text{N}}\text{2}$  and E2 reaction, respectively, when a strong nucleophile and a strong base are used.

Stereochemistry

The stereochemistry changes in the case of ${\text{S}}_{\text{N}}\text{2}$  reactions due to an inversion in the configuration. 

The configuration is S when the lowest priority groups lie in the dash position, followed by moving in an anticlockwise direction   $\text{1 → 2 → 3}$. The configuration is R when the lowest priority groups lie in the dash position, followed by moving in a clockwise direction   $\text{1 → 2 → 3}$.

Explanation

Based on all the valid explanations, The substitution and the eliminations products formed from the given compound are:

Representation of all possible eliminated and substituted products with reagent a

Representation of all possible eliminated and substituted products with reagent b