3.1.2. Drawing a reaction step rule

A reaction step rule is built from expressions, charges, electrons, lines and arrows. They are explained in 1.3 Reaction step rules. Expressions and lines extend symbols and bonds. They act like metacharacters and are interpreted in the computation when the reaction step rule has been added to the list of rules. Arrows are needed to express the movements of bonds, charges and electrons that appear in the mechanisms of organic reactions.

To place an expression on a point of the window area, first choose the appropriate operator from the menu Rules, if one is needed, then press the mouse button with the cursor on that point. A pop-up menu appears, from which a symbol can be selected to complete the expression (provided there are at least 51 pixels from all other previously drawn points and at least 20 from all previously drawn lines).

The operators that can be chosen from the menu Rules to place an expression have the following meaning:

The asterisk * matches any symbol. The expression
appears on the window area.

not excludes exactly the symbol chosen in the pop-up menu. The expression
is displayed on the window area, if the symbol X is chosen.

greater includes exactly the chosen symbol and all higher symbols. The expression
appears on the window area, if the symbol H is chosen. Here are the symbols ordered from lower to higher. Implicit sequences like Lr,...,Ac mean the corresponding sequence in the periodic table of the elements.

Lr, ..., Ac, Hg, ..., Hf, Lu, ..., La, Cd, ..., Y, Zn, ..., Sc, -, +, H, O, N, C, M, P, Q, R, ..., Z, He, ..., Ra (excluded all elements listed before), A, D, E, G, L, R0, ..., R9, M0, ..., M9.

or s means the symbol s or the symbol chosen in the pop-up menu. The expression
is displayed on the window area, if s = X and the symbol Y is chosen. In this case the expression means X or Y.

not or s means neither the symbol s nor the symbol chosen in the pop-up menu. The expression
is written on the window area, if s = X and the symbol Y is chosen. In this case the expression excludes the symbols X and Y.

cancel cancels the previous choice from the menu Rules.

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