Question

Guanidine and the guanidino group present in arginine are two of the strongest organic bases known. Account for their basicity.

Short answer

Answer: The factors that contribute to the strong basicity of guanidine and the guanidino group in arginine include the high electron density of nitrogen atoms, electronic resonance stabilization, and the planar configuration of the molecule. These factors enable efficient delocalization of electrons, stabilization when a nitrogen atom accepts a proton, and a greater ability for nitrogen atoms to act as a Lewis base.

Step-by-step solution

Introduce Guanidine and Guanidino Groups

Guanidine is a molecule with the formula C(NH2)3, and it is well known for its high basicity. Arginine is an amino acid that contains a guanidino group, which consists of a central carbon atom bonded to three nitrogen atoms in a planar configuration. The guanidino group makes arginine a strong basic amino acid.

Explain the Basicity of the Nitrogen Atoms

The basicity of a molecule is determined by its ability to accept protons (H+ ions). In guanidine and guanidino groups, there are nitrogen atoms with lone pairs of electrons that can act as a Lewis base, meaning they can donate electrons and form bonds with proton. The nitrogen atom's high electron density and availability to form bonds with protons are the reasons behind their basic character.

Describe the Electronic Resonance Stabilization

Another significant factor contributing to the high basicity of guanidine and the guanidino group is the delocalization of electrons through electronic resonance. When a nitrogen atom in the guanidine or guanidino group accepts a proton, the resulting positive charge can be delocalized across all three nitrogen atoms due to resonance. This delocalization stabilizes the molecule, making it more favorable for the nitrogen atoms to accept protons and, thus, increasing their basic character.

Address the Planar Configuration

In guanidine and guanidino groups, the nitrogen atoms and the central carbon atom are in a planar configuration. The planarity of the structure allows for better overlap of orbitals and allows for efficient delocalization of electrons, improving stabilization when a nitrogen atom accepts a proton. In conclusion, the basicity of guanidine and the guanidino group in arginine can be attributed to several factors, including the high electron density of nitrogen atoms, electronic resonance stabilization, and the planar configuration of the molecule. These factors work together to make guanidine and the guanidino group two of the strongest organic bases.