Question

Draw structural formulas for the following alcohols, and tell if each is primary, secondary, or tertiary: (a) \(1-\) butanol (b) 2-butanol (c) 3,3 -dimethyl- 2 -butanol (d) 3,3 -dimethyl- 1 -butanol

Short answer

(a) Primary, (b) Secondary, (c) Tertiary, (d) Primary

Step-by-step solution

Understand the Alcohol Types

In organic chemistry, alcohols are classified based on the carbon atom to which the hydroxyl group (-OH) is attached: primary (1°), secondary (2°), or tertiary (3°). - In **primary** alcohols, the carbon with the -OH group is attached to one other carbon. - In **secondary** alcohols, the carbon with the -OH group is attached to two other carbons. - In **tertiary** alcohols, the carbon with the -OH group is attached to three other carbons.

Draw 1-Butanol and Classify

Draw the structure of 1-butanol. The structure will have a four-carbon straight chain with the -OH group on the first carbon:\[\begin{align*}CH_3 - CH_2 - CH_2 - CH_2OH\end{align*}\]Classify: The -OH group is attached to a carbon that is only connected to one other carbon, so this is a **primary** alcohol.

Draw 2-Butanol and Classify

Draw the structure of 2-butanol. This structure has a four-carbon chain with the -OH group on the second carbon:\[\begin{align*}CH_3 - CH(OH) - CH_2 - CH_3\end{align*}\]Classify: The -OH group is on a carbon connected to two other carbons, making this a **secondary** alcohol.

Draw 3,3-Dimethyl-2-Butanol and Classify

Draw the structure of 3,3-dimethyl-2-butanol. This involves a four-carbon chain with two methyl groups on the third carbon, and an -OH on the second carbon:\[\begin{align*}CH_3 - C(OH)(CH_3) - C(CH_3)_2 - CH_3\end{align*}\]Classify: The -OH is attached to a carbon that is connected to three other carbon atoms, thus this is a **tertiary** alcohol.

Draw 3,3-Dimethyl-1-Butanol and Classify

Draw the structure for 3,3-dimethyl-1-butanol. Here, construct a four-carbon chain with two methyl groups on the third carbon, with the -OH group on the first carbon of the main chain:\[\begin{align*}C(OH)(CH_3)(CH_2-) - C(CH_3)_2 - CH_3\end{align*}\]Classify: The -OH group is attached to a carbon that is connected to only one other carbon, indicating this is a **primary** alcohol.

Key concepts

Primary Alcohol

Primary alcohols have a specific structure that makes them easy to identify. In these alcohols, the carbon atom bonded to the hydroxyl group (-OH) is attached to only one other carbon atom. This is the defining characteristic of a primary alcohol.

Let's take a closer look at 1-butanol to understand better. The structural formula of 1-butanol is:

• First, count the number of carbons in the chain from end to end. There are four carbon atoms in this case.
• The -OH group is located on the first carbon, making it a primary alcohol.
• This attachment is how you determine that 1-butanol is a primary alcohol.

In summary, remembering that the -OH group’s carbon connects to only one other carbon helps to spot primary alcohols easily.

Secondary Alcohol

Secondary alcohols are a little more complex than primary alcohols. In these structures, the hydroxyl group's carbon is attached to two other carbon atoms. Recognizing this structure will enable you to identify secondary alcohols.

Taking 2-butanol as an example:

• 2-butanol has a similar backbone of four carbon atoms in the chain.
• However, its hydroxyl group is connected to the second carbon atom, which in turn is bonded to two other carbons.
• This positions the -OH group on the secondary carbon, making it easy to classify as a secondary alcohol.

Secondary alcohols are distinguished by this particular arrangement, where the central carbon forms connections with two adjacent chains.

Tertiary Alcohol

Tertiary alcohols showcase the most branched structure among the alcohol types. In these, the carbon bearing the -OH group is linked to three other carbon atoms. This makes the identification of tertiary alcohols straightforward once you know what to look for.

Consider the structure of 3,3-dimethyl-2-butanol:

• This molecule has a branched structure where the -OH group is bonded to the second carbon.
• This specific carbon is bound to three other carbons, creating a tertiary setup.
• The branching is due to two methyl groups attached to the carbon chain, strengthening the tertiary status.

Recognizing the tertiary structure aids in understanding both the naming and classification of these alcohols.

Structural Formulas

Structural formulas are essential in organic chemistry as they depict how atoms are arranged within a molecule. For alcohols, focusing on the placement of the hydroxyl group helps understand its class.

The structural formula provides more detail compared to a molecular formula:

• For each alcohol, you need to accurately position the -OH group within a carbon chain.
• Consider the number of carbons linked to the carbon with the -OH group.
• This setup indicates whether an alcohol is primary, secondary, or tertiary.

Learning to read and draw structural formulas is crucial for mastering organic chemistry basics.

Organic Chemistry Basics

Organic chemistry basics include understanding the composition and structure of organic compounds, which are primarily built around carbon and hydrogen atoms. Recognizing different classes of compounds like alcohols is fundamental.

In organic chemistry:

• The functional groups play a critical role in the chemical behavior and classification.
• Alcohols are a classic example, where the hydroxyl group (-OH) determines their family.
• The arrangement of carbon atoms surrounding the -OH is key to understanding their reactivity and classification.

As you delve deeper into organic chemistry, mastering these basics offers a solid foundation for more complex concepts.