Volume 2 Chapter 1 Build menu SPIRO

Function

SPIRO is used to join together two fragments, with the deletion of one atom.

Examples

Ex. 1 Suppose the drawing area contains (i) - see below.

Select SPIRO

Two residues will be SPIROd together.
Select ONE ATOM from FIRST residue

Select atom a
We now have red + at atom a.
```
Select ONE ATOM from SECOND residue
```
Select atom b
We now have red + at atom b.
Screen clears and fragment is re-drawn as (ii).

Ex. 2 Suppose the drawing area contains (iii).

Select SPIRO

Two residues will be SPIROd together.
Select ONE ATOM from FIRST residue

Select atom a
We now have red + at atom a.
```
Select ONE ATOM from SECOND residue
```
Select atom b
We now have red + at atom b.
Screen clears and fragment is re-drawn as (iv).

This example illustrates the fact that the atom of the first residue determines the element type of the spiro atom after the spiro operation is complete.

Ex. 3 Although the term `spiro' normally refers to the fusion of two ring-atoms we can generalise the SPIRO option to non-ring residues.

Suppose the drawing area contains (i) - see below.

Select SPIRO

Two residues will be SPIROd together.
Select ONE ATOM from FIRST residue

Select atom a
We now have red + at atom a.
```
Select ONE ATOM from SECOND residue
```
Select atom b
We now have red + at atom b.
Screen clears and fragment is re-drawn as (ii).

You should note the following two error situations:

(a)

Suppose the drawing area contains (iii).

Select SPIRO

Two residues will be SPIROd together.
Select ONE ATOM from FIRST residue

Select atom a
We now have red + at atom a.
```
Select ONE ATOM from SECOND residue
```
Select atom a

The chosen ATOMS must be in DIFFERENT RESIDUES
Two residues will be SPIROd together.
Select ONE ATOM from FIRST residue

(b)

Suppose the drawing area contains (iv).

Select SPIRO

Two or more residues are required for SPIRO

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