XDrawChem

XDrawChem is a free software program for drawing chemical structural formulas, available for Unix and macOS. It is distributed under the GNU GPL. In Microsoft Windows this program is called WinDrawChem.

Major features

 * Fixed length and fixed angle drawing
 * Automatic alignment of figures
 * Detection of structures, text, and arrows, and their automatic placement
 * Can automatically draw rings and other structures - has all standard amino acids and nucleic acids in a built-in library
 * Retrieval of structures from a network database based on CAS number, formula, or name
 * Retrieval of information on a molecule based on a drawing
 * Symbols such as partial charge and radicals
 * Reading MDL Molfiles, CML (Chemical Markup Language), ChemDraw binary format, ChemDraw XML text format
 * Writing MDL Molfiles, CML, ChemDraw XML text format
 * Integration with OpenBabel, allowing XDrawChem to read and write over 20 different chemical file formats.
 * Image export in Portable Network Graphics (PNG), Windows bitmap, Encapsulated PostScript (EPS), and Scalable Vector Graphics (SVG)
 * 3D structure generation with the help of the external program BUILD3D
 * Simple spectra predictions, including 13C-NMR, 1H-NMR (based on additive rules and functional group lookup methods), and IR
 * Simple property estimation, including pKa, octanol-water partition coefficient, and gas-phase enthalpy change.