Spiro[2.2]pentane-1-carboxylic Acid

Spiro[2.2]pentane-2-carboxylic acid is a white to pale yellow crystalline solid with a reported melting point of 120–124°C.Its predicted boiling point is 224.3±8.0°C,and the estimated density is 1.30±0.1 g/cm³.The predicted pKa is 4.81±0.20.Storage at 2-8°C is advised.It is slightly soluble in water but dissolves readily in methanol,ethanol,THF,and DMF.It shows moderate solubility in ethyl acetate and dichloromethane and is insoluble in n-hexane.As a carboxylic acid,it is stable under dry,cool conditions but can undergo decarboxylation at temperatures significantly above its melting point.It is incompatible with strong bases(forming salts)and strong oxidizing agents.

Spiro[2.2]pentane-2-carboxylic acid(CAS No.17202-64-1)is a highly strained,symmetric carbocyclic system consisting of two fused cyclopropane rings sharing a single quaternary carbon(the spiro center).A carboxylic acid group is attached to one of the cyclopropane rings.This unique,paddle-shaped structure with high angle strain is of significant interest in physical organic and materials chemistry.

1.Strain-Release Reagent in Synthesis
The high ring strain(~27 kcal/mol per cyclopropane)drives unique reactions.It is used as a quadricyclane-like dipolarophile in strain-promoted azide-alkyne cycloadditions(SPAAC)without catalysts,enabling ultrafast bioconjugation and polymer functionalization under physiological conditions for labeling live cells.

2.High-Energy-Density Fuel Additive
Due to its strained structure and high heat of combustion,derivatives of this compound are investigated as energetic density enhancers in advanced hydrocarbon-based jet fuels.Its synthesis from renewable feedstocks is a key research area in sustainable aerospace propulsion.

3.Monomer for High-Strength,Lightweight Polyamides
Polymerized with diamines to yield polyamides where the spiro[2.2]pentane unit acts as a rigid,kinked linker.These polymers exhibit exceptional specific strength(strength-to-weight ratio),low density,and high thermal stability,targeting applications in aerospace composites and ballistic protection.

4.Probe for Studying Through-Space Electronic Effects
The proximity of the carboxylic acid to the highly strained,bent cyclopropane C-C bonds creates unique through-space electronic interactions.This compound is used in spectroscopic and computational studies to understand and quantify hyperconjugation andσ-πinteractions in distorted molecular frameworks.