Structure of a Molfile

In order to understand the Molfile format let us look at a sample file and recognize its fundamental structure. For simplicity, some less important details will be omitted in the discussion. For a complete description, users are referred to MDL s CTfile format specification [50], 

NCI Database Browser [62, 63] and only slightly modified for the purposes of this exercise. 

Each Molfile consists of two parts the so-called header block specific to Molfiles (lines 1-3) and a eonnection table - Ctab (lines 4-18), which is fundamental to all MDL s CTfile formats. 

The first line of the header block contains the molectrle name and does not require any particular format (a rare case). If no name is available the line is blank. For ethanal two names are specified its identifier within the NCI database (NSC 7594) and the regular name. 

The second line, however, has a strict format and contains general information about the user s name, the program used to generate this file, and the date and 

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