Draw three constitutional isomers with molecular formula C3H8O.
The Correct Answer and Explanation is:
Here are the three constitutional isomers for the molecular formula C3H8O.
- Propan-1-ol
Condensed Structural Formula: CH3CH2CH2OH - Propan-2-ol
Condensed Structural Formula: CH3CH(OH)CH3 - Methoxyethane (Ethyl methyl ether)
Condensed Structural Formula: CH3OCH2CH3
Explanation
Constitutional isomers are molecules that share the same molecular formula but have a different arrangement or connectivity of their atoms. For the formula C3H8O, we can construct three distinct molecules by varying the position of the oxygen atom and the carbon skeleton. This leads to two different types of functional groups: alcohols and ethers.
The first two isomers are alcohols, characterized by the presence of a hydroxyl (OH) group attached to a carbon atom.
Propan-1-ol consists of a three-carbon chain with the hydroxyl group attached to one of the terminal (end) carbons. Because the carbon bonded to the OH group is only attached to one other carbon, it is classified as a primary alcohol. Its structure is a straight chain, CH3CH2CH2OH.
Propan-2-ol also has a three-carbon chain, but the hydroxyl group is attached to the central (second) carbon atom. This makes it a secondary alcohol, as the carbon bonded to the OH group is attached to two other carbons. Its structure is CH3CH(OH)CH3. Propan-1-ol and propan-2-ol are considered positional isomers because they only differ in the position of the functional group on the same carbon skeleton.
The third isomer, Methoxyethane, belongs to a different class of compounds called ethers. In an ether, an oxygen atom is bonded to two separate carbon atoms, forming a C-O-C linkage. For C3H8O, the oxygen atom is positioned between a one-carbon methyl group (CH3) and a two-carbon ethyl group (CH2CH3). The resulting structure is CH3OCH2CH3. This molecule is a functional group isomer of the two alcohols because, while it has the same C3H8O formula, its fundamental connectivity and chemical properties are distinctly different.
