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A-Level chemistry

zushi1248

How can i differentiate between the primary and secondary alcohol?

Reply 1

LittleFire10

Original post by zushi1248

How can i differentiate between the primary and secondary alcohol?

In what way? Like do you know the difference and just need to figure it out from the name? Or do you not know the difference at all?

Reply 2

sere.moi

Original post by zushi1248

How can i differentiate between the primary and secondary alcohol?

Primary alcohol, the OH is always attached to the first carbon out of the chain length. This is so the carbon only has 1 alkyl group attached to it.

OH H H OH
| | | |
H-C-C-C-H -> H -C- CH5
| | | |
H H H H

Also when refluxed primary alcohol will turn into a carboxylic acid, when distilled will turn into a aldehyde. The positive test for a primary alcohol is with tollen’s reagent, silver lining will form on the side of the beaker.

For secondary, the OH is attached to a carbon that is attached to two more carbons. As you can see there are two alkyl groups attached to the carbon (both CH3)

H OH H OH
| | | |
H-C-C-C-H -> CH3 -C- CH3
| | | |
H H H H

When refluxed or distilled, the secondary alcohol will just turn into a ketone, it will not turn into a carboxylic acid.

I hope this helps, please just double check all I have said, I am reciting this from memory

Reply 3

sere.moi

Original post by sere.moi

Primary alcohol, the OH is always attached to the first carbon out of the chain length. This is so the carbon only has 1 alkyl group attached to it.
OH H H OH
| | | |
H-C-C-C-H -> H -C- CH5
| | | |
H H H H
Also when refluxed primary alcohol will turn into a carboxylic acid, when distilled will turn into a aldehyde. The positive test for a primary alcohol is with tollen’s reagent, silver lining will form on the side of the beaker.
For secondary, the OH is attached to a carbon that is attached to two more carbons. As you can see there are two alkyl groups attached to the carbon (both CH3)
H OH H OH
| | | |
H-C-C-C-H -> CH3 -C- CH3
| | | |
H H H H
When refluxed or distilled, the secondary alcohol will just turn into a ketone, it will not turn into a carboxylic acid.
I hope this helps, please just double check all I have said, I am reciting this from memory

Sorry I made a mistake, by alkyl I mean an R group

Reply 4

Nat4695

hi, another way I find easier, is looking at the carbon with the OH group, and checking how many hydrogen atoms that specific carbon itself is attached to;
a primary alcohol- the C with OH group is attached to 2 hydrogen atoms- or one R group such as CH3
a secondary alcohol- the C with OH group is bonded to 1 hydrogen atom
a tertiary alcohol- the C with OH group is bonded to no hydrogen atoms or 3 R groups
primary alcohol example
OH H
I I
H--C---C--H
I I
H H
the C with functional group OH, has just one hydrogen atom bonded.
youll have to forgive the atrocious format, im typing this with no way to add in a sketch.
the alcohol above is ethanol C2H5OH

(edited 1 month ago)

Reply 5

Nat4695

not sure if the typing makes the structure weird when i submit it, try searching displayed formula of ethanol and hopefully you can see more clearly what Im trying to show