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Chapter 10: Conjugation in Alkadienes and Allylic Systems
Allylic Systems |
Self Assessment |
Conjugation in Alkadienes and Allylic Systems
Resonance is probably one
of the most important concepts that one needs to master in order to understand
organic chemistry, yet it is often under appreciated or misunderstood.
We first met resonance in
Ch 1 (review)
Things to remember about
- It's a property of p
systems, therefore double or triple bonds must be present.
- Only the position of
p electrons changes in resonance contributors.
- Resonance structures
can (best) be derived by pushing curved arrows.
- The actual molecluar
structure is a composite of all the resonance contributors with the more favorable
ones contributing the most character.
- Delocalisation increases
the stablility of systems (esp. for charged systems)
of a cation
of an anion
- Functional groups next
to p systems (i.e. conjugated functional
groups) have some reactivity trends that are modified compared to those of
the non-conjugated system. Here are a few simple examples:
- allyl chloride :
very reactive in nucleophilic substitution reactions
- 1,3-butadiene : can
undergo addition via two different modes
- propenal : nucleophiles
can add to the C=C due to the presence of the conjugated C=O