IMAT 2011 Q62 [Benzene Rings]

An aromatic compound consists of two benzene rings joined together.

Which of the following could be its formula?

  1. {C_{10}H_8}
  2. {C_{10}H_{10}}
  3. {C_{10}H_{12}}
  4. {C_{12}H_{10}}
  5. {C_{12}H_{12}}

A. 1 and 4
B. 2 and 4
C. 3 and 4
D. 2 and 5
E. 3 and 5

The first possibility when two benzene rings join is that they share a side, connecting to each other with a pair of carbons.

This forms what is actually called Naphthalene, the simplest polycyclic aromatic hydrocarbon. Meaning option 1 must be correct and the only answer possible is A.

For the sake of chemistry, we could also explore different possibilities!

Option 4 is the organic compound Biphenyl. Biphenyl forms when the two benzene rings attach to each other by a double carbon bond. It ends up looking like so:

Options 2, 3 and 5 are simply not possible and therefore incorrect.