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

Compound (i).
Step 1: The carbonyl flanked by two carbons marks a ketone (suffix -one). Step 2: The parent is a six-carbon chain, so hexanone. Step 3: Numbering to give the C=O the smaller number places it at position 3 and puts the branch methyl at position 5. Step 4: Hence the name is 5-methylhexan-3-one.

Compound (ii).
Step 1: The terminal \(-CHO\) makes it an aldehyde (suffix -al) and fixes C-1 at the carbonyl carbon. Step 2: A three-carbon parent with a C2=C3 double bond gives prop-2-enal. Step 3: The benzene ring on C-3 is named as a phenyl substituent. Step 4: The IUPAC name is 3-phenylprop-2-enal, also known as cinnamaldehyde.
\[\boxed{\text{i) 5-methylhexan-3-one; ii) 3-phenylprop-2-enal}}\]