Question

Write the IUPAC nomenclature of the following organic compounds:
(A) $CH_3 - CH_2 - \overset{\text{O}}{\overset{||}{\text{C}}} - CH_2 - \underset{\text{CH}_3}{\underset{|}{\text{CH}}} - CH_3$
(B) $Ph - CH = CH - CHO$

Hint:

Priority Order for Numbering: Functional Group > Double Bond > Triple Bond > Substituents. Always start numbering to give the principal functional group the lowest possible locant.

Answer 1

(i) Structure Analysis: \[ \text{Structure:} \quad CH_3 - CH_2 - C(=O) - CH_2 - CH(CH_3)_2 \]
Longest Chain: 6 Carbons containing the ketone group.
Numbering: Start from the left to give the Ketone (functional group) the lowest number.
C1: $CH_3$
C2: $CH_2$
C3: $C=O$ (Ketone)
C4: $CH_2$
C5: $CH$ (with a methyl substituent)
C6: $CH_3$

Substituent: Methyl group at position 5.
IUPAC Name: 5-Methylhexan-3-one
(ii) Structure Analysis: \[ \text{Structure:} \quad C_6H_5 - CH = CH - CHO \]
Principal Group: Aldehyde ($-CHO$). Carbon of CHO is always C1.
Chain: Propene chain.
C1: $CHO$
C2: $CH=$
C3: $=CH-$ (attached to Phenyl ring)
Substituent: Phenyl group ($Ph-$) at C3.
Unsaturation: Double bond starts at C2.
IUPAC Name: 3-Phenylprop-2-enal (Also commonly known as Cinnamaldehyde).