Pushing Arrows Guidelines Part 3
If electrons at the tail of the arrow are nonbonding, and the atoms at the head and the tail of the arrow (A and B) are
If formation of the new bond exceeds the valency (number of allowed bonds) at the atom at the head of the arrow, a bond to that atom is broken. A second arrow is used to show this. Usually the bond broken is the σ bond to the best leaving group (X in the process below).
For any of the above processes, the
- not bonded to one another, the electron movement results in a σ bond as shown below.
- joined by a σ bond, the electron movement results in a π bond as shown below.
If formation of the new bond exceeds the valency (number of allowed bonds) at the atom at the head of the arrow, a bond to that atom is broken. A second arrow is used to show this. Usually the bond broken is the σ bond to the best leaving group (X in the process below).
For any of the above processes, the
- charge on the atom at the tail of the arrow (or series of arrows) becomes one unit more positive (A now owns fewer electrons due to being involved in an additional bond).
- charge on the atom at the head of the arrow (or series of arrows) becomes one unit more negative
- charges on any atoms that have the same number of bonds in the reactants and the products do not change
- sum of charges on products equals the sum of charges on reactants.