Question

Provide an acceptable name for each of the following. Indicate whether the amino groups in these compounds are primary, secondary or tertiary (a) \(\mathrm{CH}_{2}=\mathrm{CHCH}_{2} \mathrm{NH}_{2}\) (b) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CHNHCH}_{3}\) (c) \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{NH}_{2}\) (d) \(\mathrm{H}_{2} \mathrm{NCH}_{2} \mathrm{CO}_{2} \mathrm{H}\)

Short answer

(a) Name: 3-aminopropene, Amino group: Primary (b) Name: 2-(propylamino)butane, Amino group: Secondary (c) Name: Aniline, Amino group: Primary (d) Name: Glycine, Amino group: Primary

Step-by-step solution

Identify the functional group and parent chain

For each compound, identify the functional group (amino group, -NH2, or a derivative of it) and the parent chain (longest continuous carbon chain). (a) \(\mathrm{CH}_{2}=\mathrm{CHCH}_{2} \mathrm{NH}_{2}\): The functional group is -NH2, and the parent chain is a three-carbon chain with a double bond. (b) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CHNHCH}_{3}\): The functional group is -NH-, and the parent chain is a four-carbon chain. (c) \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{NH}_{2}\): The functional group is -NH2, and the parent chain is a benzene ring (C6H5). (d) \(\mathrm{H}_{2} \mathrm{NCH}_{2} \mathrm{CO}_{2} \mathrm{H}\): The functional group is -NH2, and the parent chain is a two-carbon chain with a carboxylic acid (-CO2H) group.

Apply IUPAC naming rules

Use IUPAC naming rules to name each compound: (a) \(\mathrm{CH}_{2}=\mathrm{CHCH}_{2} \mathrm{NH}_{2}\): The parent chain is a three-carbon chain with a double bond, so it is propene. The -NH2 group is at the end, so the name is 3-aminopropene. (b) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CHNHCH}_{3}\): The parent chain is a four-carbon chain, so it is butane. The -NH- group is connected to the second and third carbon atoms, so the name is 2-(propylamino)butane. (c) \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{NH}_{2}\): The parent chain is a benzene ring (C6H5), and the -NH2 group is attached directly to it, so the name is aniline. (d) \(\mathrm{H}_{2} \mathrm{NCH}_{2} \mathrm{CO}_{2} \mathrm{H}\): The parent chain is a two-carbon chain with a carboxylic acid group, so it is acetic acid. The -NH2 group is at the second carbon atom, so the name is glycine.

Determine the type of amino group

To determine whether the amino groups are primary, secondary, or tertiary, count the number of carbon atoms directly attached to the nitrogen atom: (a) \(\mathrm{CH}_{2}=\mathrm{CHCH}_{2} \mathrm{NH}_{2}\): One carbon atom is attached to the nitrogen atom, so the amino group is primary. (b) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CHNHCH}_{3}\): Two carbon atoms are attached to the nitrogen atom, so the amino group is secondary. (c) \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{NH}_{2}\): One carbon atom is attached to the nitrogen atom, so the amino group is primary. (d) \(\mathrm{H}_{2} \mathrm{NCH}_{2} \mathrm{CO}_{2} \mathrm{H}\): One carbon atom is attached to the nitrogen atom, so the amino group is primary. In summary: (a) Name: 3-aminopropene Amino group: Primary (b) Name: 2-(propylamino)butane Amino group: Secondary (c) Name: Aniline Amino group: Primary (d) Name: Glycine Amino group: Primary

Key concepts

Primary, Secondary, and Tertiary Amines

Amines are nitrogen-containing organic compounds that are analogous to ammonia, where one or more hydrogen atoms have been replaced by alkyl or aryl groups. These groups determine if an amine is primary, secondary, or tertiary.

In a primary amine, one alkyl or aryl group is bonded to the nitrogen atom, and two hydrogen atoms remain. Secondary amines have two organic substituents and one hydrogen, whereas tertiary amines are characterized by the presence of three organic groups attached to the nitrogen with no hydrogen atoms. For example, the compound \( \mathrm{CH}_2=\mathrm{CHCH}_2 \mathrm{NH}_2 \) is a primary amine as the nitrogen atom is connected to just one carbon atom from a propene chain.

Functional Groups in Organic Chemistry

Functional groups are specific groups of atoms within molecules that have characteristic properties and reactions regardless of the rest of the molecule's structure. In organic chemistry, these groups are the key to understanding the behavior of different organic compounds.

The amino group \( -NH_2 \) is one such functional group that defines the class of compounds termed amines. It contains nitrogen bonded to two hydrogen atoms. A major property of amines is their basicity, which is attributable to the lone pair of electrons on the nitrogen atom. Other common functional groups include hydroxyl (\( -OH \)), carbonyl (\( >C=O \) in aldehydes and ketones), carboxyl (\( -COOH \) in acids), and many others which dictate the naming and reactivity of the compounds they constitute.

Amino Acids and Their Structures

Amino acids, the building blocks of proteins, consist of a basic amino group (\( -NH_2 \) on the alpha carbon), a carboxyl group (\( -COOH \) on the same alpha carbon), an alpha hydrogen, and a distinctive side chain (R-group). The structure of amino acids is central to their classification and properties.

For instance, glycine, represented by \( \mathrm{H}_2 \mathrm{NCH}_2 \mathrm{CO}_2 \mathrm{H} \) in the exercise, is the simplest amino acid, with just a hydrogen as its side chain. The specific chemical properties of amino acids are predominantly defined by their R-groups, which vary from simple structures like in glycine to more complex ones in other amino acids.

Naming Benzene Derivatives

Benzene derivatives are aromatic compounds where one or more hydrogen atoms in the benzene ring have been replaced by other atoms or groups. The IUPAC naming of these compounds follows specific rules that consider the type of substituents and their positions on the ring.

Aniline, mentioned as \( \mathrm{C}_6 \mathrm{H}_5 \mathrm{NH}_2 \) in the exercise, is a simple example of a benzene derivative with an amino group attached to the phenyl ring. When naming, the benzene ring is identified as the parent structure, and the substituents are named and numbered according to their positions relative to each other on the benzene ring. The positions are often denoted using numbers or the prefixes ortho (o-), meta (m-), and para (p-), indicating 1,2-, 1,3-, and 1,4- relative positions, respectively.