Q13-12P - Organic Chemistry (Mcmurry)

Question

Identify the indicated sets of protons as unrelated, homotopic, enantiotopic, or diastereotopic:

a. 

(b)

(c) 

(d) 

(e) 

(f) 

Step-by-Step Solution

Answer

1. Homotopic
2. Enantiotopic
3. Homotopic
4. Diastereotopic
5. Homotopic
6. homotopic

Step 1: Types of protons

Homotopic means identical. If replacing two protons with a different group (X) gives the same compound then protons are homotopic.

If by replacing two protons with two different groups if the pair shows an enantiomeric relationship then protons are enantiotopic.

If replacing two protons with different groups gives a pair of diastereomers then the protons are diastereotopic.

Step 2: Chart for identification of proton

	Initial compound	Chiral center generated after replacement	Types of proton
1	Achiral	No chiral center generated	homotopic
2	Achiral	One chiral center generated	enantiotopic
3	Achiral	More than one chiral center generated	diastereotopic
4	chiral	No chiral center generated	Homotopic
5	Chiral	One or more than one chiral center generated	diastereotopic

Step 3: Proton identification

(a) 

The above protons are homotopic. Because after replacement no chiral center is generated.

(b)

The above protons are enantiotopic. Because after replacement one chiral center is generated.

(c) 

The protons of ${\text{-CH}}_{\text{3}}$ shows a homotopic relationship. As after there is no chiral center generated after their replacement.

(d) 

As in the above compound, one chiral center is present and after replacement also a chiral center is generated then the protons show a diastereotopic relationship.

(e) 

The protons of ${\text{-CH}}_{\text{3}}$ shows a homotopic relationship. As after there is no chiral center generated after their replacement.

(f) 

An initial molecule is achiral and after replacement, no chiral center is generated hence the protons show a homotopic relationship.