Question

Name the following alkenes. (a) \(\mathrm{CH}_{2}=\mathrm{C}-\left(\mathrm{CH}_{3}\right)_{2}\) (b) \(\left(\mathrm{CH}_{3}\right)_{2}-\mathrm{C}=\mathrm{C}-\left(\mathrm{CH}_{3}\right)_{2}\) (c) \(\mathrm{CH}_{3}-\mathrm{CH}=\mathrm{CH}-\mathrm{CH}_{2} \mathrm{CH}_{3}\) (d)

Short answer

Question: Determine the IUPAC names of the following alkenes: a) \(\mathrm{CH}_{2}=\mathrm{C}-\left(\mathrm{CH}_{3}\right)_{2}\) b) \(\left(\mathrm{CH}_{3}\right)_{2}-\mathrm{C}=\mathrm{C}-\left(\mathrm{CH}_{3}\right)_{2}\) c) \(\mathrm{CH}_{3}-\mathrm{CH}=\mathrm{CH}-\mathrm{CH}_{2}\mathrm{CH}_{3}\) d) \(\mathrm{CH}_{3}-\mathrm{CH}=\mathrm{CH}-\mathrm{CH}_{3}\) Answer: a) 2,2-dimethylethene b) 1,1,2,2-tetramethylethene c) 2-butene d) propene

Step-by-step solution

(a) Identification of the main carbon chain and numbering it

First, identify the longest carbon chain of the molecule that contains the double bond: \(\mathrm{CH}_{2}=\mathrm{C}-\left(\mathrm{CH}_{3}\right)_{2}\). It consists of 2 carbon atoms, and since the double bond is located at carbon 1, there is no need to number the chain.

(a) Naming the alkene

The main chain consists of 2 carbons with a double bond, so the base name of the molecule is "ethene". However, there are two methyl groups attached to carbon 2, so the final name is 2,2-dimethylethene.

(b) Identification of the main carbon chain and numbering it

First, identify the longest carbon chain that contains the double bond in the molecule: \(\left(\mathrm{CH}_{3}\right)_{2}-\mathrm{C}=\mathrm{C}-\left(\mathrm{CH}_{3}\right)_{2}\). It consists of 2 carbon atoms again, and since the double bond is located between carbons 1 and 2, there is no need to number the chain.

(b) Naming the alkene

The main chain consists of 2 carbons with a double bond, so the base name of the molecule is "ethene". However, there are two methyl groups attached to both carbon 1 and 2, so the final name is 1,1,2,2-tetramethylethene.

(c) Identification of the main carbon chain and numbering it

First, identify the longest carbon chain that contains the double bond in the molecule: \(\mathrm{CH}_{3}-\mathrm{CH}=\mathrm{CH}-\mathrm{CH}_{2}\mathrm{CH}_{3}\). It consists of 4 carbon atoms. Since the double bond is located between carbons 2 and 3, assign the lowest number (1) to the end carbon closest to the double bond.

(c) Naming the alkene

The main chain consists of 4 carbons with a double bond, so the base name of the molecule is "butene". However, since the double bond is located between carbons 2 and 3, the final name is 2-butene

(d) Identification of the main carbon chain and numbering it

First, identify the longest carbon chain that contains the double bond in the molecule: \(\mathrm{CH}_{3}-\mathrm{CH}=\mathrm{CH}-\mathrm{CH}_{3}\). It consists of 3 carbon atoms. Assign the lowest number (1) to the end carbon closest to the double bond.

(d) Naming the alkene

The main chain consists of 3 carbons with a double bond, so the base name of the molecule is "propene".