Question

Which of the following compounds are structural isomers of $C_5{H}_{10}O$?
(I) 2-methylbutanal
(II) Propyl ethanoate
(III) Pentanal
(IV) Pentanone

• A. I and IV
• B. I, II and III
• C. I, III and IV
• D. I and III

Answer 1

The correct option is C I, III and IV

For a compound with molecular formula $C_c{H}_h{X}_x{N}_n{O}_o$
$\text{Degree of unsaturation}=(c+1)-\frac{h}{2}-\frac{x}{2}+\frac{n}{2}$
Where, X = Halogen
c=number of carbon atom
h=number of hydrogen atom
n=number of nitrogen atom
o=number of oxygen atom
In $C_5{H}_{10}O$
$\text{Degree of unsaturation}=(5+1)-\frac{10}{2}=1$
Compound has one degree of unsaturation, it can be an aldehyde, ketone, unsaturated alcohol, etc., but can't be an ester as it contains two oxygen atoms.
2-methylbutanal and Pentanal are chain isomers of each other.
Aldehyde and ketone are functional isomers. Hence, option c is correct.