Problems and exercisesBrief History

1. Put them in order

Arrange these milestones in chronological order:

1. The hexagonal structure of benzene.
2. The discovery of nuclear magnetic resonance.
3. The synthesis of urea.
4. The tetrahedral carbon of van 't Hoff and Le Bel.

2. The end of a theory

Which theory was challenged by the synthesis of urea? Why?