F324 June 2014 OCR Q1(d)(iii)

Salicylic acid reacts with 3-hyroxypropanoic acid to form a mixture of condensation polymers. To form one polymer, the two monomers react in equal quantities. Draw the repeat unit of this polymer, displaying the link between the monomer units.

I know that the COOH on the salicylic acid reacts with the OH from the 3-hydroxypropanoic acid to form an ester link. But I don't know why the COOH on the 3-hydroxypropanoic acid from that link becomes -C=O. I also don't know why the OH on the salicylic acid becomes O-

Reply 1

aisha687

Reply 2

Pigster

Original post

by aisha687

Your first diagram shows just two monomer joining together to form a dimer.

The Q asks for the repeat unit for a polymer. Polymers keep going, and we don't show the 'ends'. Your dimer has 'ends'.

Reply 3

Amna_tutor

After you have formed an ester (like you showed in the picture), you need to remove the groups which would attach the next monomer (so it’s H from OH of salicylic acid and OH from COOH of hydroxypropanoic acid) - and that’s your polymer :smile:

Polymers should always have open bonds on the sides to show that the chain continues to grow.

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