Question

For the general formula \(\mathrm{C}_{6} \mathrm{H}_{14} \mathrm{O},\) draw the structures of three isomeric alcohols that illustrate primary, secondary, and tertiary alcohol structures.

Short answer

The isomeric alcohols with the general formula C₆H₁₄O are: 1. Primary alcohol: Hexan-1-ol (1-hexanol) - structure: CH₃-CH₂-CH₂-CH₂-CH₂-CH₂-OH 2. Secondary alcohol: Hexan-2-ol (2-hexanol) - structure: CH₃-CH(OH)-CH₂-CH₂-CH₂-CH₃ 3. Tertiary alcohol: 2-Methylpentan-3-ol (3-methyl-2-pentanol) - structure: ``` CH₃ | CH₃-C-CH₃ | CH₂-CH₃ ``` with hydroxyl group attached: ``` CH₃ | CH₃-C-OH | CH₂-CH₃ ```

Step-by-step solution

Understand the Classification of Alcohols

Alcohols can be classified into three types based on the carbon atom to which the hydroxyl group (OH) is attached. 1. Primary (1°) alcohols: The hydroxyl group is attached to a carbon atom that is bonded to only one other carbon atom. 2. Secondary (2°) alcohols: The hydroxyl group is attached to a carbon atom that is bonded to two other carbon atoms. 3. Tertiary (3°) alcohols: The hydroxyl group is attached to a carbon atom that is bonded to three other carbon atoms.

Draw a Primary Alcohol Structure

For primary alcohol, we need to attach the hydroxyl group to a carbon atom that is bonded to only one other carbon atom. In this case, let's place the OH group on the first carbon atom: CH3-CH2-CH2-CH2-CH2-CH2-OH This primary alcohol is called hexan-1-ol or 1-hexanol.

Draw a Secondary Alcohol Structure

For secondary alcohol, we need to attach the hydroxyl group to a carbon atom that is bonded to two other carbon atoms. Let's place the OH group on the second carbon atom: CH3-CH(OH)-CH2-CH2-CH2-CH3 This secondary alcohol is called hexan-2-ol or 2-hexanol.

Draw a Tertiary Alcohol Structure

For a tertiary alcohol, we need to attach the hydroxyl group to a carbon atom that is bonded to three other carbon atoms. To achieve this, let's place the OH group on the central carbon atom: CH3 | CH3-C-CH3 | CH2-CH3 CH3 | CH3-C-OH | CH2-CH3 This tertiary alcohol is called 2-methylpentan-3-ol or 3-methyl-2-pentanol. All three structures, 1-hexanol (primary), 2-hexanol (secondary), and 3-methyl-2-pentanol (tertiary), are isomeric alcohols with the general formula C6H14O and represent the primary, secondary, and tertiary alcohol structures respectively.

Key concepts

Classification of Alcohols

Understanding the classification of alcohols is fundamental in organic chemistry because it links structure to reactivity and properties. Alcohols are classified according to the number of carbon atoms connected to the carbon atom bearing the hydroxyl group (–OH).

Primary alcohols have the hydroxyl group attached to a carbon atom that is bonded to only one other carbon atom. In secondary alcohols, the hydroxyl-group-bearing carbon is connected to two other carbon atoms. Lastly, tertiary alcohols have the hydroxyl group on a carbon atom that is bonded to three other carbon atoms. This distinction is crucial as it affects the alcohol's boiling point, solubility, and how it reacts in different chemical reactions.

An easy way to remember this classification is to visualize the hydroxyl-bearing carbon as the center of a tree: primary alcohols have one branch, secondary have two, and tertiary have three.

Primary Alcohol Structure

The structure of a primary alcohol is relatively straightforward. The hydroxyl group is linked to a carbon atom that itself is connected to only one other carbon atom. This arrangement can be represented in simplified form as R-CH2-OH, where R represents the remaining carbon chain or hydrogen.

In the exercise, the example given is hexan-1-ol, or 1-hexanol. It possesses a straight-chain of six carbon atoms with the hydroxyl group at one end. This linear structure is common in primary alcohols. The importance of primary alcohols lies in their chemical reactivity, often serving as a starting point for the synthesis of other compounds through oxidation reactions.

Secondary Alcohol Structure

Secondary alcohols contain a hydroxyl group attached to a carbon atom that is bonded to two other carbons. The general formula for a secondary alcohol is represented as R1-CHR2-OH, indicating that the carbon carrying the hydroxyl group has two other carbon-containing groups attached (R1 and R2).

The drawing in the solution illustrates hexan-2-ol, or 2-hexanol, where the hydroxyl group is located at the second carbon in the chain. This position significantly alters the properties of the alcohol, making it more resistant to oxidation than its primary counterpart. Understanding the structural nuances of secondary alcohols is crucial for students aiming to predict reaction outcomes and potential applications of these molecules.

Tertiary Alcohol Structure

Tertiary alcohols are characterized by a hydroxyl group connected to a carbon atom that is joined to three other carbon atoms (R1-RC(OH)-R2, where R can be identical or different carbon chains). The structure is often depicted as a central carbon with branching chains, reflecting its three-carbon connectivity.

In our exercise, 2-methylpentan-3-ol, also known as 3-methyl-2-pentanol, is used to demonstrate a tertiary alcohol structure. This complexity gives tertiary alcohols unique chemical behaviors, such as increased steric hindrance around the hydroxyl group, which affects their reactivity, particularly making them less prone to oxidation compared to primary and secondary alcohols. Knowing tertiary structures helps students understand the synthesis and reactions of complex molecules in organic chemistry.