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6.2.15 No Cyclic Routes Instruction

• NOCR i j k ...

  This requires that atoms i,j,k,... of the search fragment cannot be connected to atoms outside the fragment by cyclic routes (bonds).

• NOCR

  This requires that no atoms of the search fragment can be connected to atoms outside the fragment by cyclic routes (bonds).

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)

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

• NOLN i j k l ...

  This requires that atoms i, j,... cannot be directly linked.

• NOLN

  This requires that no atom of the search fragment can be directly linked to any other atom of the search fragment except by the bonds specified in the 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.

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

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Volume 1 Chapter 6 Number of Fragments Instruction.