This index is a guide to organic compounds which have material constants of general interest described in the Landolt-Börnstein / New Series. In total in the subvolumes J, K, L and M, 23865 compounds with 83941 references to numerical data are recorded (K: 6181 compounds). Compiled are volumes containing nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) data, acoustical and optical properties, structure and molecular constants, mechanical and thermodynamic constants as well as physical properties of liquid crystals. All new compounds are given with the drawing of the chemical structure, the molecular formula, chemical names, the Chemical Abstracts registration numbers (CAS-RN) where known and references to Landolt-Börnstein citations.