Q.W rite IUPAC names of the products obtained by the ozonolysis of the following compounds :

Concept: Chain Isomerism – Ozonolysis cleaves the C=C bond; each carbon becomes a carbonyl group (aldehyde or ketone), depending on substitution.

Reasoning steps:

1. Pent-2-ene ($\ce{CH3-CH=CH-CH2-CH3}$): The double bond is between C2 and C3. Cleavage gives propanal ($\ce{CH3CH2CHO}$) and ethanal ($\ce{CH3CHO}$).

2. 3,4-Dimethylhept-3-ene ($\ce{CH3CH2C(CH3)=C(CH3)CH2CH2CH3}$): Both carbons of the double bond are trisubstituted → each becomes a ketone. Products: pentan-3-one ($\ce{CH3CH2COCH2CH3}$) and butan-2-one ($\ce{CH3COCH2CH3}$).

3. 2-Ethylbut-1-ene ($\ce{CH3CH2C(=CH2)CH2CH3}$): Terminal alkene → one carbon becomes formaldehyde ($\ce{HCHO}$), the other becomes pentan-3-one ($\ce{CH3CH2COCH2CH3}$). …

Ozonolysis is a classic reaction in organic chemistry where ozone ($\text{O}_3$) cleaves a carbon-carbon double bond. The key idea is that each carbon of the double bond becomes the carbonyl carbon of an aldehyde or ketone, depending on its substitution pattern. If a carbon has two hydrogens attached (terminal alkene), it gives formaldehyde ($\text{HCHO}$). If it has one hydrogen and one alkyl/aryl group, it gives an aldehyde. If it has two alkyl groups, it gives a ketone.

Let’s work through each compound step by step.

1. Pent-2-ene

   Structure: $\text{CH}_3\text{–CH=CH–CH}_2\text{–CH}_3$

   The double bond is between C2 and C3.

   • C2 has one H and one methyl group ($\text{CH}_3$), so it becomes an aldehyde: ethanal ($\text{CH}_3\text{CHO}$).
   • C3 has one H and one ethyl group ($\text{CH}_2\text{CH}_3$), so it also becomes an aldehyde: propanal ($\text{CH}_3\text{CH}_2\text{CHO}$). Products: ethanal and propanal.

2. 3,4-Dimethylhept-3-ene

   Structure: The parent chain is hept-3-ene, with methyl groups at C3 and C4. The double bond is between C3 and C4.

   • C3 has two alkyl groups (a methyl and a propyl group, since the chain continues to C1–C2–C3), so it becomes a ketone: butan-2-one ($\text{CH}_3\text{CH}_2\text{COCH}_3$).
   • C4 has two alkyl groups (a methyl and an ethyl group, since the chain continues to C5–C6–C7), so it becomes a ketone: pentan-2-one ($\text{CH}_3\text{CH}_2\text{CH}_2\text{COCH}_3$). Products: butan-2-one and pentan-2-one.
   Watch out

   A common mistake is to misidentify the alkyl groups attached to each double-bond carbon. Always draw the full structure to see which groups are directly attached to the sp² carbons. For 3,4-dimethylhept-3-ene, C3 is attached to a methyl and a propyl (not a butyl), and C4 is attached to a methyl and an ethyl (not a pentyl).

3. 2-Ethylbut-1-ene

   Structure: The name suggests a but-1-ene with an ethyl group at C2. The double bond is terminal (C1=C2).

   • C1 has two hydrogens, so it becomes formaldehyde ($\text{HCHO}$). …