Question

A functional isomer of 1-butyne is:
A. 2 -butyne
B. 1-butene
C. 2-butene
D. 1,3-butadiene

Answer 1

Hint: Functional isomerism is the type of isomerism in which molecules have the same chemical formula but different functional groups attached.

Complete step by step answer:
The structure of 1-butyne is –


That of 1,3-butadiene is –


1 butene has the structure –


2 butene has the structure –


2 butyne-


From these figures we can see that, molecular formula of both 1-butyne and 1,3-butadiene is \[{{\text{C}}_4}{{\text{H}}_6}\]. But their functional group is different. 1-butyne has \[( - {\text{C}} \equiv {\text{C}} - )\]triple bond whereas 1,3-butadiene has double bond \[( - {\text{C = C}} - )\]d. Hence, 1,3-butadiene is the functional isomer of 1-butyne.
So, option D is correct.

Additional information:
In an organic molecule, different atoms are linked to each other with different types of bonds and hence isomerism arises. Functional isomerism is a type of structural isomerism. Apart from functional isomerism, there are five more types of structural isomerism found. These are as follows -
Chain isomerism –
Two compounds having the same molecular formula but show different branched structures show chain isomerism.

Position isomerism –
Two compounds which have the same molecular formula but the position of double/triple bond varies in the chain show position isomerism.
In the above example, 1-butene and 2-butene are examples of position isomerism.

Metamerism –
This type of isomerism arises due to the presence of different alkyl chains on each side of the functional group.

Tautomerism –
When a compound shows two or more interconvertible structures which differ only in terms of relative position of atomic nucleus are called tautomers of each other and the phenomenon is called tautomerism.

Ring chain isomerism-
In ring chain type of isomerism, one structure has a long chain while the other has a ring but the molecular formulas for both are the same.

Note: Remember, when given compounds have the same molecular formula but different functional groups, they are functional isomers of each other. On the other hand, if the position of double/triple bond is different but the molecular formula is same, they show position isomerism.