Question

Write structural formulas for these amines. (a) 2 -Methyl-1-propanamine (b) Cyclohexanamine (c) \((R)-2\)-Butanamine

Short answer

Question: Draw the structural formulas for the following primary amines: (a) 2-Methyl-1-propanamine, (b) Cyclohexanamine, and (c) (R)-2-Butanamine. Answer: (a) CH3-CH(NH2)-CH3, (b) (NH2) bonded to a carbon in the cyclohexane ring, and (c) CH3-CH(NH2)-CH2-CH3 (with the 3D configuration properly represented using wedges and dashes for the (R) configuration).

Step-by-step solution

Identify Amine Structure

An amine is an organic compound derived from ammonia (NH3) in which one, two, or three hydrogen atoms are replaced by alkyl or aryl groups. In this exercise, we will focus on primary amines, which have one alkyl or aryl group bonded to the nitrogen atom. The general formula for a primary amine is R-NH2, where R is the alkyl or aryl group.

(a) 2-Methyl-1-propanamine

First, identify the main chain, which is a propane (3 carbons). Next, place a methyl group on carbon 2 and an amine group on carbon 1. The structural formula is as follows: CH3-CH(NH2)-CH3

(b) Cyclohexanamine

Identify the main structure, which is a cyclohexane. Replace one hydrogen atom in the cyclohexane with the amine group. The structural formula is as follows: ((NH2) is bonded to a carbon in the cyclohexane ring)

(c) (R)-2-Butanamine

First, identify the main chain, which is a butane (4 carbons). Next, place the amine group on carbon 2. Since the (R) configuration is specified, the amine group and the longest carbon chain should be on the same side. The structural formula for the molecule on a plane is as follows: CH3-CH(NH2)-CH2-CH3 However, it is important to note that the absolute configuration of the molecule matters, and for a complete representation, it should be drawn using wedges and dashes to indicate the 3D configuration of the molecule.

Key concepts

Primary Amines

Understanding primary amines is crucial when studying organic chemistry and tackling exercises like identifying structural formulas. A primary amine is characterized by its connection to one alkyl or aryl group. This is the simplest kind of amine, with the general structural formula of R-NH2, where R represents an organic substituent. They are formed by substituting one hydrogen atom in ammonia (NH3) with an organic group.

When dealing with exercises involving amines, pay close attention to the carbon chain length and the position where the amine group is attached. For example, in step 2 of our exercise solution, a methyl group is attached to the second carbon of a propane, making it a '2-Methyl' compound. Moreover, the placement of the NH2 group on the first carbon signals its primary nature. The exact placement of these groups in a molecule is essential in determining its properties and reactivity.

Organic Chemistry Nomenclature

The nomenclature in organic chemistry can appear daunting, but it adheres to systematic rules that make it learnable. A crucial step to mastering chemical names is recognizing the types of compounds - in this case, amines - and applying the IUPAC naming system. Here's a simplified breakdown:

• Identify the longest carbon chain in the molecule as this forms the base name.
• Number the carbons in the chain such that substituents have the lowest possible numbers.
• Name substituents (like methyl groups) and their positions on the chain.
• Finally, specify functional groups (like the NH2 of amines) and their positions.

In the exercise's Step 3, the name Cyclohexanamine emerges from the cyclohexane ring structure with an amine group attached. The prefix 'cyclo' indicates a cyclic structure, while 'hexan' refers to the hexane ring, and 'amine' denotes the presence of the NH2 group.

Stereochemistry

Stereochemistry is the study of the three-dimensional arrangement of atoms within molecules and its impact on chemical reactions and properties. It is particularly significant in chiral molecules, which have non-superimposable mirror images. These molecules are often indicated by (R) or (S) configurations, denoting their spatial orientation.

When drawing molecules, it is not sufficient to only sketch the two-dimensional structure; one must also consider the three-dimensional arrangement. In step 4 of the solution, the (R)-2-Butanamine requires depiction of the spatial arrangement. The (R) configuration denotes that the substituents are arranged in a clockwise manner when the lowest priority group is pointed away from you. The exercise advises using wedges and dashes to represent bonds coming towards or going away from the viewer, respectively.

Keep in mind, the stereochemistry can dramatically affect a molecule's function, especially in biological systems, making accurate representation of these details essential in organic chemistry.