Chemical data

• Bordwell's pKa table (Hans J. Reich)
• A values  (Hans J. Reich)
• Nucleophilicity and Electrophilicity Scales (H. Mayr);
  See also this review article

Spectral data

• Database of ¹H and ¹³C NMR, IR and MS spectra of organic compounds
• Optical Rotation Calculation

Kinetics and Thermodynamics

• Eyring Equation
• Kinetic Resolution Calculation
• Kinetics: sequential reactions and the steady state hypothesis

Periodic Table: atomic and molecular properties

• Periodic Table
• Molecular Weight Calculator
• Find Molecular Formula from Accurate Mass

General sites with lots of information

• Organic Chemistry Info (Hans J. Reich)
• Chemistry Journal Abbreviations CAS • UBC
• List of organic reactions (Wikipedia)
• Interesting problems in Organic Chemistry
• University Chemistry Departments
• Basic Terminology of Stereochemistry
• Glossary of Terms Used in Physical Organic Chemistry
• Cambridge Database - Retrieving data