## 18.1 Classification of Monohydric Alcohols Monohydric alcohols are classified into three main families based on the number of alkyl groups attached to the carbon atom bearing the hydroxyl (-OH) group. This carbon is often referred to as the carbinol carbon. ### Classification of Alcohols Monohydric alcohols are categorized into the following three types: * **(a) Primary (1°) alcohols** * **(b) Secondary (2°) alcohols** * **(c) Tertiary (3°) alcohols** ### (a) Primary Alcohols In **primary (1°)** alcohols, the carbon atom bonded to the hydroxyl group (the carbinol carbon) is attached to only *one* other alkyl group. * **General Formula:** $R-CH_2-OH$ * **Examples:** * Methanol ($CH_3OH$) * Ethanol ($CH_3CH_2OH$) * 1-Propanol ($CH_3CH_2CH_2OH$) ### (b) Secondary Alcohols In **secondary (2°)** alcohols, the carbinol carbon is attached to *two* alkyl groups. These alkyl groups can be the same or different. * **General Formula:** $R_2CHOH$ * **Example:** * Isopropyl alcohol or 2-Propanol ($CH_3CH(OH)CH_3$) ### (c) Tertiary Alcohols In **tertiary (3°)** alcohols, the carbinol carbon is attached to *three* alkyl groups. These can be the same or different. * **General Formula:** $R_3COH$ * **Example:** * Tert-butyl alcohol or 2-Methyl-2-propanol ($(CH_3)_3COH$) ## Examples Here are the structures for each class of alcohol: **Ethyl alcohol (Primary alcohol)** **Isopropyl alcohol (Secondary alcohol)** **Tert-butyl alcohol (Tertiary alcohol)** | **Alcohol Class** | **General Structure** | **Description** | **Example** | | :--- | :---: | :--- | :--- | | **Primary (1°)** | $R-CH_2-OH$ | The carbinol carbon is bonded to **one** alkyl group. | Ethanol ($CH_3CH_2OH$) | | **Secondary (2°)**| $R_2CHOH$ | The carbinol carbon is bonded to **two** alkyl groups. | 2-Propanol ($CH_3CH(OH)CH_3$) | | **Tertiary (3°)** | $R_3COH$ | The carbinol carbon is bonded to **three** alkyl groups. | 2-Methyl-2-propanol ($(CH_3)_3COH$) | This classification is crucial as the reactivity and reaction mechanisms of alcohols often depend on whether they are primary, secondary, or tertiary. For example, their oxidation behavior differs significantly. For more on functional group behavior, see .