the same header format as a non-Rgroup molfile. Counts line A counts line is required, and must be first. It specifies the number of atoms, bonds, 3D objects, and Sgroups. It also specifies whether or not the CHIRAL flag is set. Optionally, the counts line can specify molregno. This is only used when the regno exceeds 999999 (the limit of the format in the molfile header line). The format of the counts line is: SDF SDF is one of a family of chemical-data file formats developed by MDL; it is intended especially for structural information. "SDF" stands for structure-data file, and SDF files actually wrap the molfile (MDL Molfile) format. Multiple records are delimited by lines consisting of four dollar signs ($$$$). A feature of the SDF format is its ability to include associated data. Associated data items are denoted as follows: > <Unique_ID> XCA3464366 > <ClogP> 5.825 > <Vendor> Sigma > <Molecular Weight> 499.611 Multiple-line data items are also supported. The MDL SDF-format specification requires that a hard-carriage-return character be inserted if a single line of any text field exceeds 200 characters. This requirement is frequently violated in practice, as many SMILES and InChI strings exceed that length. Other formats of the family There are other, less commonly used formats of the family: RXNFile - for representing a single chemical reaction; RDFile - for representing a list of records with associated data. Each record can contain chemical structures, reactions, textual and tabular data; RGFile - for representing the Markush structures (deprecated, Molfile V3000 can represent Markush structures); XDFile - for representing chemical information in XML format. See also Chemical file format#Converting Between Formats References External links SDF Prò paid software to process SD files (SDF) from Adroit DI. SDF Toolkit free software to process SD files (SDF). NCI/CADD Chemical Identifier Resolver generates SD files (SDF) from chemical names, CAS Registry Numbers, SMILES, InChI, InChIKey, .... KNIME free software to manipulate data and do datamining, can also read and write SD files (SDF). Comparative Toxicology Dashboard service provided by the Environmental Protection Agency (EPA) which generates SD files (SDF) from chemical names, CAS Registry Numbers, SMILES, InChI, InChIKey, ... Computational chemistry Chemical file formats