Question

Give the IUPAC names of the following organic compounds:
i) \( CH_3-CH_2-CO-CH_2-CH(CH_3)-CH_3 \)
ii) \( C_6H_5-CH=CH-CHO \)

Hint:

(i) is a hexanone with a methyl branch; (ii) is an unsaturated aldehyde (cinnamaldehyde) with a phenyl group. Number to give the functional group the lowest locant.

Answer 1

Part (i): \( CH_3-CH_2-CO-CH_2-CH(CH_3)-CH_3 \)
Step 1: Identify the functional group.
The \( >C=O \) (\(CO\)) lies between two carbon atoms, so it is a ketone; the suffix is "-one".
Step 2: Choose and number the longest chain containing the carbonyl.
Longest chain: \( CH_3(1)-CH_2(2)-CO(3)-CH_2(4)-CH(5)-CH_3(6) \), a chain of 6 carbons (hexanone). Number from the end that gives the C=O the lowest locant: from the left the carbonyl is at C-3, from the right it would be C-4, so we number from the left.
Step 3: Locate substituents.
A methyl group is attached at C-5.
Step 4: Assemble the name.
5-methylhexan-3-one.

Part (ii): \( C_6H_5-CH=CH-CHO \)
Step 1: Identify the functional group.
\( -CHO \) is an aldehyde; suffix "-al", and the aldehyde carbon is always C-1.
Step 2: Number the chain.
\( CHO(1)-CH(2)=CH(3)-C_6H_5 \): a 3-carbon chain with a double bond between C-2 and C-3 and a phenyl group on C-3.
Step 3: Assemble the name.
3-phenylprop-2-enal (common name: cinnamaldehyde).

Conclusion:
\[\boxed{\text{i) 5-methylhexan-3-one} \qquad \text{ii) 3-phenylprop-2-enal}}\]