Adenine is a purine base, and as such, it contains the following functional groups:

- Two amino groups (-NH2): One amino group is located at position 6 of the purine ring, and the other is located at position 1.

- One imidazole ring: The imidazole ring is a five-membered aromatic heterocycle that contains two nitrogen atoms and one carbon atom. It is located at positions 4, 5, and 7 of the purine ring.

- One carbon-nitrogen double bond (C=N): The carbon-nitrogen double bond is located between positions 8 and 9 of the purine ring.