Volume 1 Chapter 6 Atom Property Record Exacy Value of mca

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6.2.11 Atom Property Record - nch Value

Atom property record ATp el mca nh nch E Tn A/C

The net charge, nch, on an atom can be :

Positive integers can be specified, for example, either as 2 or +2.

The three special assignments are :

In practice the use of charge in a search query is not very common. Particular care should be taken in specifying charges on transition metals since the assignment of such charges in the CSD can be somewhat arbitrary.

6.2.12 Atom Property Record - Cyclicity

Atom property record ATp el mca nh nch E Tn A/C

A indicates that the atom must be a member of a chain.

C indicates that the atom must be a member of a ring.

There is no need to specify C if the atom is part of a ring in the search fragment.

The use of A/C can be helpful in eliminating unwanted hits.

6.2.13 Atom Property Record - Unspecified Values

Atom property record ATp el mca nh nch E Tn A/C

The values of mca, nh and nch are all integers and in the interpretation of an atom property record QUEST expects them to occur in the above order.

If there is only one integer it will be interpreted as the mca value.

In this case nh and nch will be assumed to take any values.

If there are two integers these will be interpreted as mca and nh.

In this case nch will be assumed to take any value.

If you wish to specify only nh then you must code, for example: AT5 N 99 2

The value 99 means that mca is unspecified and can take any value.

If you wish to specify only nch then you must code, for example: AT5 N 99 99 +1

In this case mca and nh can take any values.

6.2.14 ALLBOND Instruction

This global instruction is used to specify that all bonds in the search fragment are acyclic or cyclic.

It takes the forms:

alternatively This instruction should be used, wherever appropriate, since it reduces computational time.

It should be specified after the atom and bond property records.

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Volume 1 Chapter 6 No Cyclic Routes Instruction.