In an oligopeptide named Alanylglycylphenyl alanyl isoleucine, the number of sp$$^2$$ hybridised carbons is _____.

Alanylglycylphenylalanylisoleucine is Ala-Gly-Phe-Ile (a tetrapeptide).

sp² hybridized carbons:

- 3 peptide bond carbonyl carbons (C=O in each peptide bond)

- 1 terminal carboxyl carbon (-COOH)

- 6 aromatic carbons in the phenylalanine benzene ring

Total = 3 + 1 + 6 = 10