Final answer:
There are three constitutional isomers for the molecular formula C₅H₁₂: pentane, isopentane (or 2-methylbutane), and neopentane (or 2,2-dimethylpropane).
Step-by-step explanation:
The question of how many constitutional isomers exist with the molecular formula C₅H₁₂ pertains to the concept of structural isomerism in organic chemistry. Structural or constitutional isomers are molecules with the same molecular formula but with different arrangements of atoms. To determine the number of constitutional isomers for pentane (C₅H₁₂), we must consider all the possible ways to arrange five carbon atoms in a chain, considering the branching that can happen.
- Pentane: This is the straight-chain isomer with all five carbon atoms in a row.
- Isopentane (also known as 2-methylbutane): This has a four-carbon chain with a methyl group attached to the second carbon.
- Neopentane (also known as 2,2-dimethylpropane): This has a three-carbon chain with two methyl groups attached to the central carbon.
In total, we can identify three constitutional isomers for the molecular formula C₅H₁₂. It is important to note that the general formula mentioned in the reference provided for calculating isomers using the number of chiral centers (2n) is applicable to stereoisomers and not constitutional isomers. Therefore, we do not use that formula in this context. Instead, we identify isomers through drawing and recognizing different structural arrangements.