Nomenclature confusion regarding carboxylate and ester
There is not supposed to be a space between the substituent prefixes (e.g. methyl) and the parent structure (e.g. propanoate), so your second structure is methylpropanoate, or more correctly 2-methylpropanoate.

In the ester there is a space between methyl and propanoate, i.e. methyl propanoate.