Which of the following chemicals is classified as not an ester?

The classification of local anesthetics is based on their chemical structure, specifically whether they are amides or esters. Benzocaine, procaine, and tetracaine all belong to the ester category due to their chemical composition, which includes an ester bond.

Dyclonine, on the other hand, is not classified as an ester. It is an exception among local anesthetics because it has a different molecular structure that features an amide bond rather than an ester bond. This structural difference affects the pharmacological properties and metabolism of the drug. Dyclonine is often used topically for its anesthetic effect, and its classification as an amide distinguishes it from the other options listed, all of which are esters associated with certain risks and considerations in local anesthesia practice.