Problem 10 - Chemistry: Principles and Reactions

Question

Follow the directions of Problem 9 for the following names. (a) 2, 2-dimethylbutane (b) 4 -methylpentane (c) 2-ethylpropane

Step-by-Step Solution

Answer

Question: Draw the structural formulas for the following alkanes: (a) 2,2-Dimethylbutane (b) 4-Methylpentane (c) 2-Ethylpropane. Answer: (a) 2,2-Dimethylbutane: CH3 | CH3-CH-C-CH2-CH3 | CH3 (b) 4-Methylpentane: CH3-CH2-CH2-CH-C-CH3 | CH3 (c) 2-Ethylpropane: CH2-CH3 | CH3-CH-C-CH3 | CH3

Step 1: (a) 2,2-Dimethylbutane)

(First, identify the main carbon chain in the name, which is butane. Butane consists of a 4-carbon chain, represented as C-C-C-C. Next, find the branching group(s), which are 2 methyl groups (CH3) in this case. The numbers in the name, 2,2, represent the positions of the two methyl groups on the main carbon chain. Now, draw the structural formula by attaching the two methyl groups at the second carbon in the butane chain. The resulting structure should look like this: CH3 | CH3-CH-C-CH2-CH3 | CH3)

Step 2: (b) 4-Methylpentane)

(First, identify the main carbon chain in the name, which is pentane. Pentane consists of a 5-carbon chain, represented as C-C-C-C-C. Next, find the branching group, which is a methyl group (CH3) in this case. The number 4 in the name represents the position of the methyl group on the main carbon chain. Now, draw the structural formula by attaching the methyl group at the fourth carbon in the pentane chain. The resulting structure should look like this: CH3-CH2-CH2-CH-C-CH3 | CH3)

Step 3: (c) 2-Ethylpropane)

(First, identify the main carbon chain in the name, which is propane. Propane consists of a 3-carbon chain, represented as CH3-CH2-CH3. Next, find the branching group, which is an ethyl group (CH2CH3) in this case. The number 2 in the name represents the position of the ethyl group on the main carbon chain. Now, draw the structural formula by attaching the ethyl group at the second carbon in the propane chain. The resulting structure should look like this: CH2-CH3 | CH3-CH-C-CH3 | CH3)

Key Concepts

Structural Formula

In organic chemistry, the structural formula is a crucial way to represent molecules. Instead of just showing the total number of each atom, the structural formula provides a detailed depiction of how the atoms are arranged and bonded together.

This visualization helps in understanding the molecule's shape and properties.

• For instance, 2,2-dimethylbutane shows two methyl groups (CH3) attached to the second carbon of a butane chain.
• Meanwhile, 4-methylpentane demonstrates a single methyl group attached to the fourth carbon of a pentane chain.
• In 2-ethylpropane, an ethyl group (CH2CH3) is attached to the second carbon of a propane chain.

Identifying and drawing the structural formula starts by identifying the longest carbon chain and then placing substituents, such as methyl or ethyl groups, at the correct positions as indicated by the numbers in the compound name.

Carbon Chains

Carbon chains form the backbone of organic compounds and determine the primary structure of a molecule. These chains consist of carbon atoms linked together, forming either straight (linear) or branched structures.

Carbon's ability to form stable chains and bonds with other elements, especially hydrogen, gives rise to the diversity of organic chemistry.

• In the compound names discussed, butane has a chain of four carbons (C-C-C-C), pentane has five carbons, and propane has three.
• Upon identifying the main chain, we can understand how substituents are structured around this chain, affecting the molecule's properties.

The length and shape of the carbon chain are significant because they influence the boiling point and solubility of the compound in other solvents.

Substituent Groups

Substituent groups are vital in organic chemistry as they modify the properties and reactivity of hydrocarbons. These groups, which branch off from the main carbon chain, can include a variety of atoms or groups of atoms.

In organic molecules, substituents like methyl (CH3) or ethyl (CH2CH3) play a role in determining the molecule's overall behavior.

• The location of these groups is given by numbers in the name. For example, the name 2,2-dimethylbutane indicates two methyl groups attached to the second carbon.
• In 4-methylpentane, the methyl group is on the fourth carbon, and for 2-ethylpropane, the ethyl group is on the second carbon.

These small changes to the structure can significantly alter the molecule’s physical and chemical properties, making the accurate placement of substituent groups critical for understanding a molecule's activity.