Answer
The IUPAC names for the compounds are as follows:
(a) 1-methylcyclopentene
(b) 2-methylbutane
(c) 2-butyne
(d) 2-methyl-2-butene
(e) 3-methylpentane
(f) 3-ethylhexane
Work Step by Step
(a) This is a cyclic alkene where five carbon atoms make up the ring, so the root name is cyclopentene. The methyl group is on a carbon that bears the double bond. The smallest possible number assignable to the carbon bearing the double bond is 1.
(b) The longest continuous carbon chain has four carbons, and so the root name is butane. There is a methyl group attached to the penultimate carbon at one end of the chain. The smallest possible locant would be obtained by numbering the carbon chain beginning at the terminal carbon closest to the methyl group.
(c) The longest continuous carbon chain that contains the triple bond has four carbons, so the root name is butyne. Regardless of the terminal carbon at which one begins numbering, the smallest locant for the triple bond will be 2.
(d). The longest continuous carbon chain that contains the double bond has four carbons, so the root name is butene. Regardless of the terminal carbon at which one begins numbering, the smallest locant for the double bond will be 2. The methyl group is located on carbon 2.
(e) The longest continuous carbon chain has five carbons, and so the root name is pentane. There is a methyl group attached to carbon 3 regardless of which terminal carbon one begins to count the carbon chain.
(f) The longest continuous carbon chain has six carbons, and so the root name is hexane. There is an ethyl group attached to carbon 3 regardless of which terminal carbon one begins to count the carbon chain.
