- You recall from CH 334 the special reactivity of allylic (and benzylic) positions. You remember how to write resonance structures for allylic radicals and cations, and can explain what these mean in terms of the MOs of these systems.
Visualization: MOs of the 1,3-dimethylallyl cation and radical.
- You can predict that allylic radicals and cations can form multiple products that are explained by the resonance/MO description of the intermediate.
- You know that NBS is a more easily controlled source of Br2 for radical allylic bromination (particularly in light of the alkene addition chemistry of bromine).
- You understand the high reactivity of allylic alcohols and halides to SN1 substitutions.
- You can recognize the difference between conjugated and nonconjugated dienes (and polyenes) and describe that difference in MO terms related to pi-orbital interactions.
Visualization: MOs of 1,3-Butadiene
- You know that conjugation stabilizes dienes and polyenes.
- You know that electrophilic addition to a conjugated system generates a delocalized carbocation, that multiple products are possible, and that thermodynamic control (high temperature, usually favoring 1,4-addition) or kinetic control (low temperature, usually favoring 1,2-addition) can often change the product mixture.
- You can recognize the thermal reaction of a diene with a monoalkene to form a cyclohexene: the Diels-Alder reaction. You can correctly arrange how substituents in the reactants will appear in the product, including the stereochemical relationships.
- You know that the Diels-Alder reaction has a concerted mechanism, usually uses an electron-rich diene and an electron-poor alkene ("dienophile"), and usually follows the endo rule.
Visualization: The Diels-Alder Reaction
Recommended end-of-chapter problems: 14-32, 14-34, 14-36, 14-37, 14-41 (a, b, c, d, f only), 14-47, 14-49, 14-55, 14-58, 14-59, 14-63, 14-66.
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