Volume 1 Chapter 6 Atom Property Record nch Value

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6.2.15 No Cyclic Routes Instruction

The NOCR instruction can be used to restrict the environment of the search fragment and can take two forms:

The instruction can be used only once per connectivity test and should be specified after the atom and bond property records.

Consider the search fragment (a) below, with target structures (i)-(iv).

NOCR
This will register hits only for (i)
NOCR 3
This will register hits for (i) and (ii)
NOCR 6
This will register hits for (i),(iii) and (iv)
NOCR 4 5
This will register hits for (i) and (iii)
Now consider the search fragment (b) below.

This has topological symmetry. Thus if we wish to apply NOCR to atom 2 then it must also be applied to atom 6.

NOCR 2 6
This will register a hit for (v) but not for (vi).

6.2.16 No Direct Links Instruction

The NOLN instruction can be used to place restrictions on the search fragment. and can take two forms :

The instruction can be used only once per connectivity test and should be specified after the atom and bond property records.

Consider the search fragment (a) below, with target structures (i)-(iii).

NOLN 3 8
This will registers hits for (i),(ii),(iii)
NOLN 4 7
This will registers hits for (ii),(iii)
NOLN
This will registers hits only for (ii) Atoms 4 and 7 are connected by an indirect link through a bridging carbon atom.
NOLN 3 6 8 5
This will registers hits for (i),(ii)

Since the search fragment has topological symmetry a link 3-6 would be equivalent to a link 8-5. Thus to exclude (iii) you must code both possibilities.

Note that if atom numbers are specified in a NOLN instruction ranges can be used.

Thus NOLN 1-6 9 12-14 is a valid instruction.

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Volume 1 Chapter 6 Number of Fragments Instruction.