Part 8: MECHANISMS

Note that no other reagents are needed in order to complete any of these sequences, you should only be using what is there.

Here are links to answers or a quick overview to keep you going until complete images can be provided.

Part A

i   
Nitration of a benzene, via electrophilic aromatic substitution.
ii    Fischer esterification = ester synthesis
iii   Protonate the alkene to give the secondary carbocation..... 1,2-hydride shift to the more stable tertiary carbocation then loss of the H+ will give the more stable alkene


Part B

Attention to detail, challenge questions, you will not have seen these examples before BUT if you know your reactions and have good problem solving skills and know the tools, then you should be able to work-out the answers....

i   
Look carefully... what type of reaction is the bromination ? It's not electrophilic aromatic substitution.... where is the catalyst or count the C=C or check the aromaticity of the middle ring : don't forget the H atoms.   It's actually a 1,4-conjugate addtion of a halogen with the middle ring reacting as a conjugated diene. 
Now what about to the right, the maleic anhydride ... hmm..... a good dienophile.... just talked about a conjugated diene, so Diels-Alder reaction across the middle ring again....
Note that both these reactions leave 2 benzene rings which are more stable than 1 naphthalene system (resonance energies)
ii    The product is a conjugated enone, this is a good indicator of aldol type chemistry.
First, deprotect the acetal to reveal the aldehyde.  Now do the aldol via the enol form of the ketone onto the more electrophilic aldehyde, and dehydrate to give the more stable conjugated product.

 


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