Question

Ciprofloxacin is a member of the fluoroquinolone class of antibiotics.(b) Which nitrogen atoms are basic?

Accepted Answer

Identify the structure of ciprofloxacin, which contains multiple nitrogen atoms in its molecular framework. These nitrogen atoms can be part of aromatic rings, amines, or other functional groups. Recall the concept of basicity in organic chemistry: a nitrogen atom is considered basic if it has a lone pair of electrons that can accept a proton (H⁺). The availability of this lone pair is influenced by the electronic environment around the nitrogen. Examine each nitrogen atom in the structure of ciprofloxacin. Determine whether the lone pair on each nitrogen is delocalized (shared in resonance) or localized. If the lone pair is delocalized, the nitrogen is less basic because the lone pair is not readily available for protonation. Pay special attention to nitrogen atoms in aromatic systems (e.g., pyridine-like or pyrrole-like rings). In pyridine-like systems, the lone pair is not involved in aromaticity and is available for protonation, making the nitrogen basic. In pyrrole-like systems, the lone pair is part of the aromatic system and is not available for protonation, making the nitrogen non-basic. Conclude which nitrogen atoms in ciprofloxacin are basic by identifying those with localized lone pairs that are not involved in resonance or aromaticity. These are the nitrogen atoms capable of accepting a proton.

Ciprofloxacin is a member of the fluoroquinolone class of antibiotics.

(b) Which nitrogen atoms are basic?

Verified video answer for a similar problem:

Key Concepts

Basicity in Organic Chemistry

Structure of Ciprofloxacin

Hybridization and Basicity