Question 18M.2.sl.TZ2.a
| Date | May 2018 | Marks available | [Maximum mark: 2] | Reference code | 18M.2.sl.TZ2.a |
| Level | sl | Paper | 2 | Time zone | TZ2 |
| Command term | Discuss | Question number | a | Adapted from | N/A |
The structure of an organic molecule can help predict the type of reaction it can undergo.
The Kekulé structure of benzene suggests it should readily undergo addition reactions.
Discuss two pieces of evidence, one physical and one chemical, which suggest this is not the structure of benzene.
[2]
Physical evidence:
equal C–C bond «lengths/strengths»
OR
regular hexagon
OR
«all» C–C have bond order of 1.5
OR
«all» C–C intermediate between single and double bonds
Chemical evidence:
undergoes substitution reaction «more readily than addition»
OR
does not discolour/react with bromine water
OR
substitution forms only one isomer for 1,2-disubstitution «presence of alternate double bonds would form two isomers»
OR
more stable than expected «compared to hypothetical molecule cyclohexa-1,3,5-triene»
OR
enthalpy change of hydrogenation/combustion is less exothermic than predicted «for cyclohexa-1,3,5-triene»
M1:
Accept “all C–C–C bond angles are equal”.
[2 marks]