In my chemistry study material a set of rules to draw resonance structures are given. They are:
(1) Only electrons move. The nuclei of the atoms never move.
(2) The only electrons that can move are pi electrons (electrons in pi bonds) and lone-pair electrons.
(3) The total number of electrons in the molecule does not change, and neither does the number of paired and unpaired electrons.
The electrons can be moved in one of the following ways:
(a) Move pi electrons toward a positive charge or towards a pi bond.
(b) Move lone-pair electrons toward a pi bond.
(c) Move a single non-bonding electron toward a pi bond.
As an illustration of the second part of point (a)- move pi electrons towards a pi bond, 22.jpg is given which has been attached with this answer.
In the first and second examples pi electrons are moving towards sigma bond and not pi bonds. Right? Then how does this support the first rule that "Move pi electrons...towards a pi bond."? Where am i going wrong?

Abhishek Parida, 6 years ago

Grade:10

1 Answers

Pooja

askIITians Faculty 477 Points

5 years ago

Dear student,
Actually your question is quite valid as it is very confusing for us to understand but these authors write something like this and then not following such rules while drawing resonance structures. But see the resonance means the delocalization of electrons. In the structure you have mentioned- kindly allow the electrons to move to the sp2 hybridized carbons, its the single -double bond movement. You are not wrong its a hypothetical process which occurs only in our imagination.
Please read further at the following link\
https://www.askiitians.com/iit-jee-chemistry/organic-chemistry/iupac-and-goc/electronic-displacement-in-covalent-bonds/#resonance-&-mesomeric-effect