Question

Draw line structures for the following amines. (a) \(\left(\mathrm{CH}_{3}\right)_{2} \mathrm{NH}\) (b) \(\left(\mathrm{CH}_{3}\right)_{2} \mathrm{NC}_{2} \mathrm{H}_{5}\) (c) \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{NH}_{2}\)

Short answer

For \(\left(\mathrm{CH}_{3}\right)_{2} \mathrm{NH}\), the line structure shows one nitrogen atom connected to three carbon atoms, each of which is then connected to three hydrogen atoms. For \(\left(\mathrm{CH}_{3}\right)_{2} \mathrm{NC}_{2} \mathrm{H}_{5}\), the line structure shows a nitrogen atom connected to two carbon atoms (that are each linked with three hydrogen atoms) and one ethyl group (a carbon chain with hydrogens attached). For \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{NH}_{2}\), the line structure consists of an NH2 group attached to a benzene ring. These structures of amines are in line with their formulas.

Step-by-step solution

Identify the Atoms and Connect Them Correctly

For the first amine \(\left(\mathrm{CH}_{3}\right)_{2} \mathrm{NH}\), there are two CH3 groups and one NH. Start by drawing the N atom in the center, then draw the two CH3 groups connected to it. Each CH3 group consists of a C atom connected to three H atoms.

Draw the Line Structure for the Second Amine

For the second amine \(\left(\mathrm{CH}_{3}\right)_{2} \mathrm{NC}_{2} \mathrm{H}_{5}\), two CH3 groups are present as well as an NC2H5 group. Start by drawing the N atom, then add the two CH3 groups and the C2H5 group. Each CH3 group again consists of a C atom connected to three H atoms while the C2H5 group is composed of two C atoms connected in a line with 5 hydrogens atoms.

Draw the Line Structure for the Final Amine

For the third amine \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{NH}_{2}\), there is one C6H5 group and one NH2 group. Start by drawing the NH2 group then, draw a benzene ring (a six membered ring alternating between single and double bonds) to represent the C6H5 group. Finally, connect them together.

Key concepts

Chemical Structure Representation

Understanding the chemical structure representation is central to mastering organic chemistry. In essence, a chemical structure tells us about the arrangement of atoms in a molecule. This can be represented in various ways, such as structural formulas, where single lines represent single bonds, double lines double bonds, and triple lines triple bonds. However, it is important to be familiar with molecular or empirical formulas as they are the basis upon which these representations are built. For example, in the exercise, the molecular formula for the amines provides the number of carbon (C), hydrogen (H), and nitrogen (N) atoms in each compound.

When drawing chemical structures, it's critical to connect atoms correctly based on their valence, which dictates how many bonds an atom can form. For instance, carbon typically forms four bonds, nitrogen forms three, and hydrogen forms one. By adhering to these bonding rules, we can ensure that the structures we draw are chemically plausible. The structures were successfully drawn by starting with the nitrogen and adding the relevant groups such as CH3 (methyl) or C6H5 (phenyl), being mindful of the specific bonding patterns of each atom involved.

Amines in Organic Chemistry

Amines are fundamental components in organic chemistry and are characterized by their nitrogen atom bonded to hydrogen atoms or alkyl or aryl groups. They are derived from ammonia (\(NH_3\)) by replacing one or more hydrogen atoms with carbon-containing groups, which influences their properties and reactivity.

In the exercises provided, different types of amines are demonstrated—with primary (\(NH_2\) group), secondary (two alkyl groups and one hydrogen on nitrogen), and tertiary (three alkyl groups on nitrogen) amines. The first example is dimethylamine, a simple secondary amine. The second is N,N-dimethylethanamine, a tertiary amine, and the third is aniline, a primary aromatic amine, with the phenyl group attached to the NH2 group. These amines showcase the variety of organic compounds where nitrogen plays a crucial role, and each has unique structural and chemical properties that contribute to their wide uses in pharmaceuticals, dyes, and polymers.

Line Structure Notation

The line structure notation, also known as skeletal structure or bond-line notation, is a shorthand representation of molecules commonly used in organic chemistry. It allows chemists to draw complex structures more quickly and with less clutter than detailed structural formulas. In this system, each vertex or end of a line indicates a carbon atom, and hydrogen atoms are usually omitted for brevity unless they are attached to heteroatoms like nitrogen or oxygen.

In the provided exercise, the line structure notation simplifies the drawings of amines. For instance, the methyl groups are represented simply by two lines stemming from the central nitrogen atom in the first compound. The N,N-dimethylethanamine is depicted with lines for carbon atoms and the nitrogen connected to the ethyl group. The aromatic compound aniline uses a hexagon for the benzene ring, showcasing the alternating double and single bonds. The goal of these representations is to provide a clear and straightforward way to visualize the molecular structure, focusing on the connectivity rather than all the individual atoms, making complex organic molecules easier to interpret and understand.