Question

Question: Acyclovir is an effective antiviral agent used to treat the herpes simplex virus. (a) Draw the enol form of acyclovir, and explain why it is aromatic. (b) Why is acyclovir typically drawn in its keto form, despite the fact that its enol is aromatic?

Short answer

Answer

(a) The enol form of acyclovir is shown below:-

The enol form is acidic because it follows Huckel’s rule of (4n+2)$\pi$electrons where the value of n is 2.

(b) Acyclovir is typically drawn in its keto form, even though its enol is aromatic because they exist in the form of intramolecular H-bonding state as a four-membered ring in keto form.

Step-by-step solution

Stability of the aromatic compound

Acyclovir in enol form is aromatic because it follows Huckel’s rule (4n+2) $\pi$ electrons. The aromatic compounds are stable because they obey Huckel’s rule where delocalization of (4n+2)$\pi$ electrons takes place.

Representation of the aromatic Acyclovir

Intramolecular H-bonding

Acyclovir prefers to exist in keto form due to its ability to undergo intermolecular H-bonding and exists as a four-membered ring.

Representation of the intramolecular H-bonding state of Acyclovir

Considering the steps, the answer is provided.

(a) The enol form of acyclovir is shown below:-

Representation of the enol form Acyclovir

The enol form is acidic because it follows Huckel’s rule of (4n+2)$\pi$ electrons where the value of n is 2.

(b)Acyclovir is typically drawn in its keto form, even though its enol is aromatic because they exist in the form of intramolecular H-bonding state as a four-membered ring in keto form.

Representation of the keto form Acyclovir