Questions of the Day a DielsAlder reactions are

Questions of the Day: a) Diels-Alder reactions are what type of reactions? b) Which structural feature is always formed as the result of Diels-Alder reactions? c) What is a “good diene” (i. e. one that reacts fast in Diels. Alder)? d) What would be a good dienophile?

Today: • Diels-Alder (cont. ), NMR • Esterification (Exp. 5), a first introduction • Mini. Quiz

Diels-Alder reactions require a 1, 3 -diene (in s-cis) and a dienophile (an alkene, best when EWG is attached). 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 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 Synthesis of Natural Products C Steroids! A B D

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

Diels Alder The H-NMR of the dimer of 1, 3 -cyclopentadiene 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?

Methyl Benzoate Synthesis (Exp. 5) the first step of a two- step synthesis 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? • Fats and Oils • Waxes • Ripening process in fruits • phosphate esters in DNA

Salicin and Aspirin Salicin in willow bark (Salix)

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

Mini. Quiz 4 Problems: 1) Draw a simple, but clear H-NMR for alpha - monobromoethylbenzene 2) Draw a simple, but clear H-NMR for alpha - dibromoethylbenzene