Question

For a branched unsaturated acyclic hydrocarbon, the parent chain is the longest carbon chain that contains the;
A. Maximum number of double bonds
B. Maximum number of triple bonds
C. Both A and B
D. None of these

Answer 1

A acyclic hydrocarbon has the general formula of ${{\text{C}}_{\text{n}}}{{\text{H}}_{{\text{2n + 2}}}}$ and therefore consisting entirely of hydrogen atoms and saturated carbons. In our case we have a branched unsaturated hydrocarbon, a branch in the parent chain can also be called a substitution.

Complete answer:
Let’s look at the meaning of unsaturated hydrocarbon chain, an unsaturated carbons consist of double and triple covalent bonds between two adjacent carbon atoms, this is called unsaturated because we can add more hydrogen atoms to make the hydrocarbon chain saturated (i.e., consisting of only carbon-carbon single covalent bonds).
Now, the substitution in a hydrocarbon chain can be of anything, it could be of a functional group (-al, ol, one, oic acid), another carbon chain (-ethyl, -propyl, -butyl), there could be cyclic substitution also (benzene, pyridine, cyclopentane), etc.
As we know that unsaturated hydrocarbon has double and triple bonds, therefore the parent chain that will have the maximum number of the double and triple bonds would be considered as the parent chain.

**Hence, the correct option is (C)i.e., both A and B

Additional information:**
Longest Carbon chain: Well according to IUPAC nomenclature, the first and foremost thing we do while naming a hydrocarbon chain is to determine its parent chain.

Note:
This step is used when there is a tie between two hydrocarbon chains, having the same number of carbon atoms, the tie is then broken by considering the chain having the maximum number of unsaturated carbons. i.e, the maximum number of double and triple bonds.