Question

Chain and position isomerism are shown in:
[A] Alkane
[B] Alkene
[C] Alkyne
[D] All of the above

Answer 1

HINT: To answer this, you need to remember what chain and position isomerism is. In chain isomerism, one isomer might be a straight chain and the other branched but their chemical formula will be the same. In position isomerism, the position of bonds or substituents will differ in isomers.

Complete step by step solution:
To answer this, firstly we have to discuss what isomerism is. Isomerism is the phenomenon where two or more chemical compounds have the same chemical formula but different chemical structures. The compounds showing isomerism are known as isomers. Now, let us discuss what chain and position isomerism is.
- Chain isomerism – When two or more compounds have the same chemical formula but not the same carbon skeleton, then the compounds are known as chain isomers and the phenomenon is known as chain isomerism.
Example: Pentane, isopentane and neopentane are examples of chain isomers. They have the same chemical formula i.e. $C_5{H}_{12}$ but the structure is different.
Now, we will discuss this isomers for alk – ane, ene and yne by taking suitable examples.
For alkanes, n-butane is a straight chain compound whereas iso-butane is branched. For alkenes, oct – 1 – ene is straight chain but methyl hept – 1 – ene is branched. For alkynes, oct – 1 – yne is straight chain but methylhept – 1 – yne is branched. So, they show chain isomerism
- Position isomerism – The isomers where the position substituents, functional group or the double bonds are different in two compounds, then the phenomenon is known as position isomerism.
Example: Propan – 1 – ol and Propan – 2 – ol are examples of position isomerism as they have the same structure except the position of the –OH group which differs in the two compounds.
Now, we will discuss this isomers for alk – ane, ene and yne by taking suitable examples.
In alkanes, 2 – methylpentane and 3 – methylpentane are position isomers and similarly for alkenes, 1 – heptene and 2 – heptene and for alkynes, 1 – butyne and 2 – butyne are position isomers as position of double and triple bonds respectively are different. We can understand from the above discussion that Chain and position isomerism are shown by alkanes, alkenes and alkynes.

Therefore, the correct answer is option [D] All of the above.

NOTE: The two kinds of isomerism that we discussed above were structural isomerism. There are other isomers under this category like functional isomerism, ring-chain isomerism, metamerism and tautomerism. Besides structural isomerism, organic compounds also show stereoisomerism where the chemical formula and the sequence of bonding is the same but they differ in their spatial arrangements.