Chemical table file (CT File) is a family of text-based chemical file formats that describe molecules and chemical reactions. One format, for example, lists each atom in a molecule, the x-y-z coordinates of that atom, and the bonds among the atoms. File formats There are several file formats in the family. The formats were created by MDL Information Systems (MDL), which was acquired by Symyx Technologies then merged with Accelrys Corp., and now called BIOVIA, a subsidiary of Dassault Systemes of Dassault Group. CT File is an open format, BIOVIA publishes its specification. BIOVIA requires users to register to download the CTFile format specifications. Molfile An MDL Molfile is a file format for holding information about the atoms, bonds, connectivity and coordinates of a molecule. The molfile consists of some header information, the Connection Table (CT) containing atom info, then bond connections and types, followed by sections for more complex information. The molfile is sufficiently common that most, if not all, cheminformatics software systems/applications are able to read the format, though not always to the same degree. It is also supported by some computational software such as Mathematica. The current de facto standard version is molfile V2000, although, more recently, the V3000 format has been circulating widely enough to present a potential compatibility issue for those applications that are not yet V3000-capable. Counts line block specification Bond block specification The Bond Block is made up of bond lines, one line per bond, with the following format: 111 222 ttt sss xxx rrr ccc where the values are described in the following table: Extended Connection Table (V3000) The extended (V3000) molfile consists of a regular molfile “no structure” followed by a single molfile appendix that contains the body of the connection table (Ctab). The following figure shows both an alanine structure and the extended molfile corresponding to it. Note that the “no structure” is flagged with the “V3000” instead of the “V2000” version stamp. There are two other changes to the header in addition to the version: The number of appendix lines is always written as 999, regardless of how many there actually are. (All current readers will disregard the count and stop at M END.) The “dimensional code” is maintained more explicitly. Thus “3D” really means 3D, although “2D” will be interpreted as 3D if any non-zero Z-coordinates are found. Unlike the V2000 molfile, the V3000 extended Rgroup molfile has