Question

$C{H}_3-\stackrel{OH}{\stackrel{|}{CH}}-\underset{OH}{\underset{|}{CH}}-\stackrel{C{H}_3}{\stackrel{|}{CH}}-CHO$

The IUPAC name is:

• A. 4-hydroxy-1-methylpentanal
• B. 3, 4-dihydroxy-2-methylpentanal
• C. 2-hydroxy-4-methylpentanal
• D. 2, 3-dihydroxy-4-methylpentanal

Answer 1

The correct option is B 3, 4-dihydroxy-2-methylpentanal

$\underset{5}{C{H}_3}-\stackrel{OH}{\stackrel{|}{\underset{4}{CH}}}-\underset{OH}{\underset{|3}{CH}}-\stackrel{C{H}_3}{\stackrel{|}{\underset{2}{CH}}}-\underset{1}{CHO}$

Aldehyde has higher priority than alcohol, so the numbering is done as shown in the figure. The longest continuous chain contains 5 carbon atoms and at $3^{rd}$ and $4^{th}$ position hydroxy group is present. At $2^{nd}$ carbon atom, one methyl group is present. Alphabetically 'h' comes first than 'm'.

Hence, the IUPAC name is $3,4$- dihydroxy -$2$- methyl Pentanal