Mini Quiz 2 Questions a Write the structure

Mini. Quiz 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) • Mini. Quiz

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

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

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

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

CH 3 C CH 3 A CH 3 D CH 3 B HO Cholesterol

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

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?

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?

Esters and Esterifications 1. General properties of esters? 2. Compare the boiling points of carboxylic acids and esters of similar molecular weight and explain. 3. Examples of esters in biological systems?

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