Question: Anacin is an over-the-counter pain reliever that contains aspirin and caffeine. Answer the following questions about each compound:

a. What is the molecular formula?

b. How many lone pairs are present on heteroatoms?

c. Label the hybridization state of each carbon.

d. Draw three additional resonance structures.

The individual atom’s count, which is taking part in the skeletal structure, is shown in the compact structure. So, the compact structure of the corresponding skeletal structure is known as the molecular formula.

The number of lone pairs is determined based on the valence electrons and bonding pairs.

Suppose an atom has six valence electrons and two bond pairs, so now the atom is left with 4 electrons or two lone pairs.

The multiplicity of bonds usually determines the hybridization as mentioned below:

• The single-bonded carbon has ${\mathrm{sp}}^3$ hybridization.
• The double-bonded carbon has ${\mathrm{sp}}^2$ hybridization.
• The triple-bonded carbon has $\mathrm{sp}$ hybridization.

a. The skeletal structure of aspirin is formed by nine carbons, four oxygens, and eight hydrogens. Therefore, its molecular formula is ${\mathrm{C}}_9{\mathrm{H}}_8{\mathrm{O}}_4$.

The skeletal structure of caffeine is formed by 8 C, 2 O, 4 N, and 10 H. Therefore, its molecular formula is ${\mathrm{C}}_8{\mathrm{H}}_{10}{\mathrm{N}}_4{\mathrm{O}}_2$.

b. In the skeletal structure of aspirin and caffeine, oxygen and nitrogen are heteroatoms.

In the case of aspirin, oxygen has six valence electrons, and only two of them are involved in forming the bond.

Thus, the two lone pairs are available on each oxygen atom. Hence, a total of eight lone pairs are present in the structure.

In the case of caffeine, nitrogen has five valence electrons, and only three of them are involved in forming the bond.

Thus, the one lone pair is available on each nitrogen atom. Hence, eight lone pairs (four on nitrogen and four lone pairs on oxygen) are present in the structure.

c. In the skeletal structures of aspirin and caffeine, it is clear that only double bonds and single bonds are present. So,${\mathrm{sp}}^3$ hybridization is placed on single-bonded carbon and ${\mathrm{sp}}^2$for double-bonded carbon.

Aspirin Caffeine

d.Resonance shows the hypothetical images obtained when pi electrons or non-bonding electrons move from one orbital to another.

Here, the resonance structures of aspirin and caffeine are represented as follows:

Resonance structures of aspirin

Resonance structures of caffeine