Delocalization and conjugation
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What do p orbitals have to be in order for the pi bond to form?
Parallel
Why does the pi bond prevent rotation around C=C?
At 90 degrees there is no overlap and therefore the pi bond is broken
What is a conjugated system?
An overlapping series of p orbitals (at least 3)
What does conjugation result in?
Delocalisation of electrons Lower energy so therefore thermodynamically more stable
What type of orbital can be involved in conjugation?
sp2
Because the charge is shared symmetrically across the allyl cation, what does this mean for nucleophilic attack?
Attack either end of the molecule with equal probability
What do resonance forms show?
The various possible ways to arrange double bonds and delocalised electrons
What are resonance arrows?
Double headed arrows
Where does the true structure of a molecule lie?
In between the resonance forms
What are the two reasons to use resonance forms?
To draw mechanisms To predict reactivity
Why do resonance forms help to draw mechanisms?
If it shows the charge as shared across the molecule and not resonance forms, it is difficult to see what the product will be
How do resonance forms help to predict reactivity?
Helps you to see where is more likely to be protonated
If conjugation can happen…
It WILL
What is involved in conjugation?
Lone pair, cation, empty p orbital or radical next to a pi bond (double bond)
Why will conjugation always happen if it can?
It lowers the energy of the system