A level chem desperate help

Cant hack this question at all. Surely if the carboxyl group counts as the first carbon then it can’t be 4-amino 3methylbutanoic acid (this is the mark scheme answer btw)

Why isntit 2 amino 3methylbutanoic acid

(edited 5 years ago)

Original post by arielynjoan

You have 'split' the repeating units in the wrong place. The amine group of one monomer and the carboxylic acid of the next monomer unit formed the bond, hence you must split the chain at the bond between the N and the carbonly carbon.
This will give you the monomer named in the mark scheme.

Reply 3

arielynjoan

If I split it between the N and the C, then where does the carboxyl group in the 4amino 3 methylbutanoic acid come into play? I thought they had to be together judging from the ms answer?

Reply 4

ChemistryWebsite

Original post by arielynjoan

If I split it between the N and the C, then where does the carboxyl group in the 4amino 3 methylbutanoic acid come into play? I thought they had to be together judging from the ms answer?

The carboxyl group in the polymer derives from the carboxylic acid group in the monomer.
In the monomer structure you have drawn at the bottom of page 2 (your first image) you have a nitrogen within the main chain. The C-N-C only forms during the condensation of the monomer, so that should be your alarm bell in future that it isn't correct.

Here's the repeating unit and the monomer :