Question

(a) What is meant by the term isomer? (b) Among the four alkanes, ethane, propane, butane, and pentane, which is capable of existing in isomeric forms?

Short answer

(a) The term isomer refers to a compound with the same molecular formula but different structural formulas, meaning the atoms are arranged differently within the molecules. (b) Among the given alkanes (ethane, propane, butane, and pentane), both butane and pentane are capable of existing in isomeric forms.

Step-by-step solution

Part (a): Definition of Isomer

An isomer is a compound with the same molecular formula but different structural formulas. In other words, isomers have the same number and type of atoms, but the atoms are arranged differently within the molecules. This can result in different physical and chemical properties for compounds with identical molecular formulas.

Part (b): Identifying the Alkane with Isomeric Forms

To find which of the given alkanes can exist in isomeric forms, we need to first understand their molecular structures. Alkanes are hydrocarbons with only single bonds between carbon atoms (C) and hydrogen atoms (H). The general formula for alkanes is \(C_nH_{2n+2}\), where n is the number of carbon atoms in the molecule. Given the four alkanes: 1. Ethane (\(C_2H_6\)): It has two carbon atoms and six hydrogen atoms. 2. Propane (\(C_3H_8\)): It consists of three carbon atoms and eight hydrogen atoms. 3. Butane (\(C_4H_{10}\)): It has four carbon atoms and ten hydrogen atoms. 4. Pentane (\(C_5H_{12}\)): It has five carbon atoms and twelve hydrogen atoms. Alkanes can exist in isomeric forms if their carbon atoms are arranged in different ways, resulting in different structural formations. Ethane and propane have too few carbon atoms to form isomers, as the carbon atoms form a single and linear structure. However, butane and pentane have enough carbon atoms to potentially form isomeric structures. In butane, the four carbon atoms can form two isomers: normal (n-) butane and isobutane (also known as methylpropane). In pentane, three isomers are possible: normal (n-) pentane, isopentane (also called 2-methylbutane), and neopentane (2,2-dimethylpropane). Thus, among the four alkanes provided (ethane, propane, butane, and pentane), both butane and pentane are capable of existing in isomeric forms.