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MiniQuiz 2 Questions:

MiniQuiz 2 Questions:. a) Write the structure of the radical formed when Br . radical reacts with ethyl benzene. b) Why is there no radical formation in the beta position of ethyl benzene?. Today: Diels-Alder (cont.) Esterification (Exp.5) MiniQuiz. Diels-Alder Reaction.

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MiniQuiz 2 Questions:

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  1. MiniQuiz 2 Questions: a) Write the structure of the radical formed when Br. radical reacts with ethyl benzene. b) Why is there no radical formation in the beta position of ethyl benzene?

  2. Today: • Diels-Alder (cont.) • Esterification (Exp.5) • MiniQuiz

  3. Diels-Alder Reaction The Diels-Alder reaction requires a 1,3-diene and a dienophile. The Diels-Alder reaction involves a 1,4-addition of an alkene to a 1,3-diene in an electrocyclic reaction (a “cycloaddition”). 4 1 D.-A. adduct The 1,3-diene must be in s-cis conformation The dienophile is an alkene; it is most reactive if EWG’s are attached

  4. Diels – Alder Reactions Which of the following dienes would be most reactive? why? 1,3-cyclopentadiene, 1,3-butadiene (see problems on Report Form) Which of the following dienophiles would be more reactive? Ethene or maleic anhydride

  5. Diels – Alder Reactions (Exp.4) Which structural feature is always formed as the result of Diels-Alder reactions?

  6. Diels – Alder Reactions Synthesis of Natural Products D C A B

  7. CH3 CH3 D C CH3 CH3 A B HO Cholesterol

  8. Diels – Alder Reactions Reaction equations for our experiment: Retro Diels Alder:Cracking of dimer Diels Alder: Reaction of 1,3-cyclopentadiene with maleic anhydride Hydrolysis of Diels-Alder product Dimer D.-A. adduct Cis endo • Compare: • Polarity of I versus II • Mp. of I versus II

  9. Diels Alder The H-NMR of the dimer of 1,3-cyclopentadiene (dicyclopentadiene) is quite complex, with many signals. In contrast, the proton NMR of our Diels-Alder product is simple, with few signals; the same is true for its hydrolysis product. How can you explain this?

  10. Exp.5:Methyl Benzoate Synthesis(first step for Exp.6 Grignard) You will heat your reaction under reflux for 1 hour! Do Practice Problems, calculations … • In order to increase the yield of the ester, which of the following would help? • use an excess of methanol • use an excess of conc. sulfuric acid • Calculations …! Why sulfuric acid and not HCl?

  11. Esters and Esterifications • General properties of esters? • Compare the boiling points of carboxylic acids and esters of similar molecular weight and explain. • Examples of esters in biological systems?

  12. Next time: Conclusion of “Esterification” (Exp. 5) Grignard reactions (Exp. 6) MiniQuiz on today’s lab lecture!

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