One of the ASCII representations of the molecule is the Nancy Linear Form (NLF). This represents a 2-D Lewis structure representation of a molecule. This means that 3-D information and the position of the atoms is only implied by the atoms and the valence structure. Nancy linear form is similar to the SMILES representation and is used in the original THERGAS and EXGAS programs. Linear, branched and (multiple) ringed structures, aromatics and radicals can be represented by this format. The Nancy linear form is the primary mode of inputting structures into the database (particularly ASCII file input).
In Nancy linear form, atoms are designated by their atomic name in lower case. If the name consists of two characters, then the name is put in quotes:
Carbon: c
Hydrogen: h
Oxygen: o
Bromine: 'br'
Chlorine: 'cl'
If an atom is a radical, then a (.) is put next to the atom:
Hydrogen radical: h(.)
Bromine radical: 'br'(.)
Connectivity is represented in several ways. First, direct connectivity, such as with methane, is represented by listing the connecting atoms directly after the central atom (what is considered central is fairly arbitrary):
ch4
where the 4 designates that there are 4 hydrogens attached. Other examples include:
nitrosyl chloride: 'cl'no
hypofluorous acid: fho
nitrogen dioxide: no2
perchloric acid: 'cl'ho4
Another way to denote connectivity is with slashes:
Single bond: /
Double bond: //
Triple bond: ///
For example:
octane: ch3/ch2/ch2/ch2/ch2/ch2/ch2/ch3
2-hexene: ch3/ch//ch/ch2/ch2/ch3
propyne: ch///c/ch3
Further branching is denoted by surrounding the branched chain in parentheses. The connected group within parentheses is repeated, then as before, a number is attached denoting how many. Some examples are:
2-methylpropene: ch2//c(ch3)/ch3
ter-butyl alcohol: c(ch3)3/oh
isopropyl alcohol: ch3/ch(oh)/ch3
Rings are denoted using a (#n), where n is a number denoting which ring and denotes the 'start' of the ring, and a paired n, which denotes the end of the nth ring. Some examples are:
cyclopropene : c(#1)h//ch/ch2/1
azulene: c(#1)/c(#2)/ch//ch/ch//ch/ch//1,1/ch//ch/ch//2
oxirane: c(#1)h2/ch2/o/1
methyl cyclopentane: ch(#1)(ch3)/ch2/ch2/ch2/ch2/1
Aromatic bonds are denoted with &. . For example:
benzene: c(#1)h&ch&ch&ch&ch&ch&1
phenol: c(#1)(oh)&ch&ch&ch&ch&ch&1
naphtalene: c(#1)&c(#2)&ch&ch&ch&ch&1,1&ch&ch&ch&ch&2
In addition, there are some meta-atoms which can be used, such as carbon monoxide, 'co', sulfur dioxide, 'so2', and nitryl, 'no2'. These are included in quotes. For example:
2-pentanone: ch3/'co'/ch2/ch2/ch3
iso-nitropropane: ch3/ch'no2'/ch3
dimethylsulfone: ch3/'so2'/ch3