Rules of the Day
4-11-2024
Featured Golden Rule of Chemistry:
5. Delocalization of charge over a larger area is stabilizing.
6. Delocalization of unpaired electron density over a larger area is stabilizing.
7. Delocalization of pi electron density over a larger area is stabilizing.1
Click here for a copy of the lectures notes I wrote in class
Click here for a copy of the handouts I used in class today
1. Knowing when to use phenyl vs. benzyl can be tricky!
2. As the result of the benzyl radical stability, it is easy to carry out free radical halogenation of the benzyl position using X2 and light or heat.
3. Alkyl groups on benzene rings are oxidized all the way to carboxylic acids using Na2Cr2O7/H2SO4 (H2CrO4) as long as there is at least one benzylic hydrogen atom on that alkyl group.
4. Electrophilic aromatic substitution involves wicked strong electrophiles reacting with the aromatic pi system to create a resonance stabilized arenium ion intermediate that then loses a proton to give the substitution product.
5. Make sure you know the reagents needed for each reaction, as well as the nature of the "wicked strong" electrophile on the handouts from class. Click here for the first handout, and click here for the second. Students often forget when to use FeX3 vs. AlX3 as catalysts. Remember that the FriedAL-Crafts used ALuminum (AlX3). OK, so I had to spell Friedel wrong, but I am trying to help here!
6. Both Friedel-Crafts reactions (alkylation and acylation) will not work if there is a strongly deactivating (BAD) group on the ring. The Friedel-Crafts alkylation is also a slow reaction, meaning the carbocation intermediates will rearrange if possible. In fact, primary haloalkanes will always rearrange to more stable secondary carbocations during the reaction, that then add to the aromatic ring by attaching through the secondary carbon. Rearrangement prone secondary carbocations will also only give rearranged products. The Friedel-Crafts acylation does NOT rearrange.
7. A workaround to avoid primary haloalkane rearrangemet in the Friedel Crafts alkylation reaction is to use the Friedel-Crafts acylation to create a ketone (with no rearragement) followed by a Wolff-Kischner or Clemmensen reduction to remove the ketone carbonyl group and give the desired alkane group on the ring.
Beta-dicarbonyl enolate stericsLinks to an external site.
When to use NaOH vs. NaOEtLinks to an external site.
What is meant by "H3O+"Links to an external site.
Balancing an equation for the Claisen reactionLinks to an external site.
What is up with -OH, -OEt and LDA in enolate reactions? (mistake on the last page edition)!Links to an external site. Click here to see the corrected version of the -OH, -OEt and LDA in enolate reaction video.Links to an external site. YOU NEED TO WATCH BOTH VIDEOS...AND IN ORDER.
Homework:
Read: No reading due to the exam. This text is part of the Longhorn Textbook access program.
There are no quizzes or homeworks this week because of the exam on tonight.