Question

An alkene X on ozonolysis gives a mixture of simplest ketone (Y) and 3-Pentanone. The IUPAC name of the alkene X is

• A. 2,3-Dimethylbut-2-ene
• B. 3-Ethyl-4-methylpent-3-ene
• C. 3-Ethyl-2-methylpent-2-ene
• D. 2-Methyl-3-ethylpent-2-ene

Hint:

Reverse Ozonolysis Trick: Write the two carbonyl products facing each other: \( >\text{C=O} \quad \text{O=C}< \). Erase the O's and connect the carbons with a double bond: \( >\text{C=C}< \).

Answer 1

The Correct Option is C

Step 1: Identify the Ozonolysis Products:
1. Simplest Ketone (Y): The simplest ketone is Propanone (Acetone). Structure: \(\text{CH}_3\text{-C(=O)-CH}_3\) 2. 3-Pentanone: A 5-carbon ketone with the carbonyl group at the 3rd position. Structure: \(\text{CH}_3\text{-CH}_2\text{-C(=O)-CH}_2\text{-CH}_3\)
Step 2: Determine Structure of Alkene X:
Ozonolysis cleaves a double bond \( \text{C=C} \) and places an Oxygen on each carbon atom to form two carbonyl compounds \( \text{C=O} + \text{O=C} \). To find the original alkene, we reverse this process: remove the oxygen atoms and join the carbonyl carbons with a double bond. \[ [\text{Propanone}] = \text{(CH}_3)_2\text{C=O} \] \[ [\text{3-Pentanone}] = \text{O=C(CH}_2\text{CH}_3)_2 \] Joining them: \[ \text{(CH}_3)_2\text{C} = \text{C(CH}_2\text{CH}_3)_2 \] Expanded Structure: \[ \text{CH}_3\text{-C(CH}_3)\text{=C(CH}_2\text{CH}_3)\text{-CH}_2\text{CH}_3 \]
Step 3: IUPAC Naming of X:
1. Select Principal Chain: The longest carbon chain containing the double bond. Path: \(\text{CH}_3\text{-C-C-C-C}\) is a 5-carbon chain. (Parent: Pentene). 2. Numbering: Start from the end that gives the double bond the lowest number. - From Left: \( \text{C}^1\text{H}_3\text{-C}^2(\text{CH}_3)\text{=C}^3(\text{CH}_2\text{CH}_3)\text{-C}^4\text{H}_2\text{-C}^5\text{H}_3 \) \(\rightarrow\) Double bond at C-2. - From Right: Double bond starts at C-3. Correct numbering is from the left. 3. Identify Substituents: - At C-2: Methyl group (\(-\text{CH}_3\)) - At C-3: Ethyl group (\(-\text{CH}_2\text{CH}_3\)) 4. Assemble Name: Substituents in alphabetical order (Ethyl before Methyl). \(3-Ethyl-2-methylpent-2-ene\). Final Answer:
Option (C).