Primary, Secondary & Tertiary Alcohols

An alcohol is classified as primary, secondary or tertiary NOT because of where the OH is attached. It is all about the Carbon on which the OH is attached.

We will call the carbon on which the -OH is attached, the key carbon, and in these examples, it is in red.

Primary Alcohols

Notice the red key carbon, where the -OH is attached.
butan-1-ol



Only one other carbon, the green carbon, is attached to the key carbon.
Hence this is a primary alcohol.

N.B.
In this example, even though the red key carbon is not attached to another carbon, this is still called a primary alcohol.


Secondary Alcohols

Notice the red key carbon, where the -OH is attached.
butan-2-ol



There are two other carbons, the green carbons, attached to the key carbon.
Hence this is a secondary alcohol.

Tertiary Alcohols

Notice the red key carbon, where the -OH is attached.
2-methylbutan-2-ol



There are three other carbons, the green carbons, attached to the key carbon.
Hence this is a tertiary alcohol.
It does not matter how complicated the molecule may appear. Just identify the key carbon, and then count how many other carbons are attached to it.

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