The computer program SPARC (SPARC Performs Automated Reasoning in Chemistry) has been under development for several years to estimate physical properties and chemical reactivity parameters of organic compounds strictly from molecular structure. SPARC uses computational algorithms based on fundamental chemical structure theory to estimate a variety of reactivity parameters. Resonance models were developed and calibrated on more than 5000 light absorption spectra, whereas electrostatic interaction models were developed using more than 4500 ionization pKas in water. Solvation models (i.e., dispersion, induction, dipole-dipole, hydrogen bonding, etc.) have been developed using more than 8000 physical property data points on properties such as vapor pressure, boiling point, solubility, Henry's constant, GC retention times, Kow, etc. At the present time, SPARC predicts ionization pKa (in the gas phase and in many organic solvents including water as function of temperature), carboxylic acid ester hydrolysis rate constants (as function of solvent and temperature), E1/2 reduction potential (as function of solvents, pH and temperature), gas phase electron affinity and numerous physical properties for a broad range of molecular structures.