The key difference between primary and secondary alcohol is that the carbon atom that carries the -OH group in primary alcohol is attached only to one alkyl group whereas the carbon atom that carries the -OH group in secondary alcohol is attached to two alkyl groups.

Alcohol is an organic compound that contains a hydroxyl group as the functional group. Therefore, the reactivity of the alcohol molecules depends upon the location of the hydroxyl group in the molecule. Accordingly, there are three major types as primary, secondary and tertiary alcohols, depending on the way that the hydroxyl group attaches to the molecule.

CONTENTS

1. Overview and Key Difference
2. What is Primary Alcohol
3. What is Secondary Alcohol
4. Side by Side Comparison – Primary vs Secondary Alcohol in Tabular Form
5. Summary

What is Primary Alcohol?

Primary alcohol is an organic compound in which the carbon atom that carries the -OH group is only attached to one alkyl group. That means; the carbon atom containing the functional group attaches with one other carbon atom while the other atoms that attach to this carbon atom are hydrogen atoms. Hence, there always only one alkyl linkage for the hydroxyl group-containing a carbon atom.

However, the smallest primary alcohol, methanol has only three hydrogen atoms bonded to the carbon atom carrying the hydroxyl group, and there are no alkyl linkages. Most of the times, primary alcohol is linear in structure, but there can be some branching if the molecule is very large. However, primary alcohol is less stable because there is only one alkyl linkage to the carbon atom that carries the –OH group.

What is Secondary Alcohol?

Secondary alcohol is an organic compound in which the carbon atoms that carry the –OH group attached to two alkyl groups. Therefore, this carbon atom has one hydrogen atom attached to it along with the hydroxyl group and two alkyl groups. Hence, there are two alkyl linkages to this carbon atom. Furthermore, upon oxidation under mild conditions, these molecules convert into ketones.

Moreover, secondary alcohol is more stable since they have two alkyl linkages. And also, these molecules easily undergo esterification when compared to primary alcohols. However, these organic compounds are less acidic.

What is the Difference Between Primary and Secondary Alcohol?

Primary alcohol is an organic compound in which the carbon atom that carries the -OH group is only attached to one alkyl group whereas secondary alcohol is an organic compound in which the carbon atoms that carry the –OH group attached to two alkyl groups. Therefore, this is the key difference between primary and secondary alcohols. Moreover, reactiveness of each contributes to another difference between primary and secondary alcohols. The primary alcohols are comparatively less reactive while secondary alcohols are more reactive.

However, primary alcohols are less stable because there is only one alkyl linkage to the carbon atom that carries the –OH group while secondary alcohols are more stable since they have two alkyl linkages. Thus, stability also a factor in the difference between primary and secondary alcohols. More details on the difference between primary and secondary alcohols are given in the below infographic.

Summary – Primary vs Secondary Alcohol

Alcohols are hydroxyl group-containing organic compounds. There are three major types according to the structure; primary, secondary and tertiary alcohols. The key difference between primary and secondary alcohol is that in primary alcohol, the carbon atom that carries the -OH group is only attached to one alkyl group whereas, in secondary alcohol, the carbon atom that carries the -OH group is attached to two alkyl groups.

Reference:

1. “Chemistry.” Primary, Secondary & Tertiary Alcohols | BYJU’S. Available here   
2. “Primary Alcohol.” Wikipedia, Wikimedia Foundation, 5 Sept. 2018. Available here  

Image Courtesy:

1.”Ethanol-2D-skeletal”By Bryan Derksen – Own work, (Public Domain) via Commons Wikimedia 
2.”Alcohol examples”By Walkerma (Public Domain) via Commons Wikimedia