Number of carboxylic acids and esters isomers for C4H8O2

[TT0]

Homework Statement

What is the total number of isomeric carboxylic acids and esters having the molecular formula C4H8O2?

A.6

B.5

C.4

D.3

E.2

Homework Equations

The Attempt at a Solution

My answer was 4. The isomers I got was:

-2-methyl propanoic acid
-butanoic acid
-methyl propanoate
-ethyl ethanoate

Did I miss any?

Cheers!

 

[Ygggdrasil]

What about esters based on formic acid?

 

[TT0]

I see, I missed propyl methanoate. Cheers!

 

[Ygggdrasil]

There are two isomers based on formic acid.

 

[TT0]

I see, I forgot isopropyl acetate. So the answer is A. Cheers!