Question

Distinguish among primary, secondary, and tertiary alcohols. Give a structural formula for an example of each type.

Short answer

Primary, secondary, and tertiary alcohols are distinguished based on the number of carbon atoms bonded to the carbon atom attached to the hydroxyl group (OH). In primary alcohols, the carbon atom is bonded to only one other carbon atom and two hydrogen atoms (e.g., ethanol: CH3CH2OH). In secondary alcohols, the carbon atom is bonded to two other carbon atoms and one hydrogen atom (e.g., isopropanol: CH3CHOHCH3). In tertiary alcohols, the carbon atom is bonded to three other carbon atoms and has no hydrogen atoms bonded to it (e.g., tert-butanol: \(C(CH_3)_3OH\)).

Step-by-step solution

Understanding primary, secondary, and tertiary alcohols.

Primary, secondary, and tertiary alcohols are classified based on the number of carbon atoms bonded to the carbon atom that is attached to the hydroxyl group (OH). 1. Primary alcohols (1°): The carbon atom attached to the hydroxyl group is bonded to only one other carbon atom and two hydrogen atoms. 2. Secondary alcohols (2°): The carbon atom attached to the hydroxyl group is bonded to two other carbon atoms and one hydrogen atom. 3. Tertiary alcohols (3°): The carbon atom attached to the hydroxyl group is bonded to three other carbon atoms and has no hydrogen atoms bonded to it.

Providing a structural formula for a primary alcohol.

An example of a primary alcohol is ethanol, which has the following structural formula: CH3CH2OH Here, the carbon atom attached to the hydroxyl group is bonded to only one other carbon atom (CH3) and two hydrogen atoms (H and H).

Providing a structural formula for a secondary alcohol.

An example of a secondary alcohol is isopropanol, which has the following structural formula: CH3CHOHCH3 In this structure, the carbon atom attached to the hydroxyl group is bonded to two other carbon atoms (CH3 and CH3) and one hydrogen atom (H).

Providing a structural formula for a tertiary alcohol.

An example of a tertiary alcohol is tert-butanol, which has the following structural formula: \(C(CH_3)_3OH\) In this case, the carbon atom attached to the hydroxyl group is bonded to three other carbon atoms (CH3, CH3, and CH3) and has no hydrogen atoms directly attached to it.

Key concepts

Primary Alcohols

Primary alcohols are the most straightforward type of alcohol to understand. The defining feature of a primary alcohol is the carbon atom directly attached to the hydroxyl group (-OH). This carbon atom is bonded to only one other carbon atom and typically two hydrogen atoms.

• The general formula for a primary alcohol can be represented as RCH2OH, where R is the alkyl group connected to the single carbon.
• Ethanol ( CH3CH2OH) is a classic example of a primary alcohol, where the carbon linked to the OH group connects to one other carbon and bears two hydrogens.

Characteristics of Primary Alcohols

Primary alcohols are often seen as more reactive towards oxidation compared to secondary and tertiary alcohols. They can be oxidized to form aldehydes and further oxidized to carboxylic acids. This makes them quite versatile in organic synthesis.

Secondary Alcohols

In secondary alcohols, the carbon atom attached to the hydroxyl group (-OH) is bonded to two other carbon atoms and typically one hydrogen atom. This setup distinguishes them from both primary and tertiary alcohols.

• The general formula is R1R2CHOH, where R1 and R2 are the alkyl groups.
• Isopropanol ( CH3CHOHCH3) serves as an example of a secondary alcohol. Here, the central carbon is linked to two methyl groups and bears one hydrogen atom.

Oxidation and Reactions

Secondary alcohols can be oxidized to ketones, known for their distinct properties and usefulness in various chemical reactions. However, unlike primary alcohols, they do not further oxidize to carboxylic acids. This property is particularly useful in organic chemistry for differentiating between primary and secondary alcohols.

Tertiary Alcohols

Tertiary alcohols have a more complex structure where the carbon atom bound to the hydroxyl group (-OH) is connected to three other carbon atoms and no hydrogen atoms directly attached to the hydroxyl-bearing carbon.

• The general structure for a tertiary alcohol is R1R2R3COH, with three alkyl groups coming off the central carbon.
• An example of a tertiary alcohol is tert-butanol, which has the structure C(CH3)3OH, where the central carbon links to three methyl groups.

Distinguishing Features and Reactivity

Tertiary alcohols resist oxidation reactions that primary and secondary alcohols undergo. Due to the absence of hydrogen atoms on the carbon holding the hydroxyl group, they can't be oxidized further under normal conditions. This feature makes them relatively stable, providing different applications and reactions in industrial and laboratory settings.