Draw the structural formula of the repeating unit in Kevlar.

Explain how the long rigid chains in Kevlar are able to form cross-links to build up a three-dimensional structure.

Award [1] for correct showing of amide linkage.

Award [1] for remainder of structure correct.

Accept H and O both up or both down or accept –NH–CO– but do not accept –N–H–CO–.

Brackets not necessary to gain marks.

the \({\delta ^ - }\)/lone pair on the O of the C=O and the \({\delta ^ + }\) on the H of the N–H / the polarity of the C=O and the N–H bonds;

Accept N-H of one chain and C=O of adjacent chain or NH₂ group of one chain with C=O group of another chain.

(form) hydrogen bonds / OWTTE;

Accept suitable diagram.

There were very few correct answers for this question with many blank answer boxes. In a) i), only a small number of candidates gave correct answers here. Many incorrectly gave the group –CHO instead of –CH₂OH as a substituent on the ring.

There were very few correct answers for this question with many blank answer boxes. In a) i), only a small number of candidates gave correct answers here. Many incorrectly gave the group –CHO instead of –CH₂OH as a substituent on the ring.