Guanidine

Guanidine, HN=C(NH₂)₂, is a strongly basic nitrogen-rich organic compound. Its derivatives include the amino acid arginine and compounds used in medicines and industry.

Imine: An organic compound containing a carbon–nitrogen double bond. Guanidine’s central carbon forms an imine bond to one nitrogen.
Brønsted–Lowry acid–base theory: A theory defining acids as proton donors and bases as proton acceptors. Guanidine acts as a base by accepting a proton from an acid.
Arginine: A protein-building amino acid whose side chain contains a guanidino group. Arginine is guanidine’s prominent biological derivative and carries a guanidinium group.
Ammonia: A nitrogen hydride with the formula NH₃ that acts as a weak base in water. Unlike ammonia, guanidine’s conjugate acid distributes charge over several nitrogen atoms.
Amidine: An organic functional group with a carbon bonded to an amino group and an imine nitrogen. Guanidine is the simplest member of this closely related functional-group family.
Conjugate acid: The species formed when a base accepts a proton. Guanidinium is the conjugate acid produced by protonation of guanidine.
Creatine: A nitrogen-containing compound that helps buffer and supply energy in muscle and other tissues. Creatine and its biosynthesis involve guanidino compounds.
Urea: A carbon-containing compound with formula CO(NH₂)₂, produced in protein metabolism. Replacing guanidine’s imine nitrogen with oxygen changes basicity and biological role.
Resonance (chemistry): A model that represents delocalized electrons using multiple contributing Lewis structures. Resonance spreads positive charge across guanidinium’s three nitrogen atoms.
pKa: A logarithmic measure of an acid’s tendency to donate a proton in solution. The pKa of guanidinium quantifies how strongly guanidine binds a proton.

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