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che 325 lab 4 guide

che 325 lab 4 guide - EXPERIMENT 2(Organic Chemistry II...

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EXPERIMENT 2 (Organic Chemistry II) Pahlavan/Cherif Diels-Alder Reaction Preparation of ENDO-NORBORNENE-5, 6-CIS-CARBOXYLIC ANHYDRIDE Purpose a) Study conjugated dienes b) Study diene and dienophile c) Study cycloaddition reaction Chemicals Materials Maleic anhydride 125 ml Erlenmeyer flask Ethyl acetate 400 ml Beaker Cyclopentadiene Hot water bath Hexane ( OR Petroleum ether) Ice bath Mel-temp Suction filtration funnel REACTION + O O O O O H H O Cyclopentadiene Maleic anhydride ENDO-Norbornen-5,6-cis-dicarboxylic anhydride C 5 H 6 M.W. = 66.10 g/mol C 4 H 2 O 3 M.W. = 98.06 g/mol C 9 H 8 O 3 M.W. = 164.15 g/mol B.P. = 41.5 42.0 0 C M.P. = 52.8 0 C M.P. = 164 - 165 0 C M.P. = -85 0 C Cis- butanoic anhydride Density = 0.80 g/ml (20-25 0 C) 2,5- furandioic anhydride Toxilic anhydride 1
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Introduction The Diels-Alder reaction is one of the most powerful tools used in the preparation of important organic molecules. When two carbon-carbon double bonds are positioned next to one another, a conjugated diene is formed. A non- conjugated diene is a molecule that has two olefins which are not next to each other. Conjugated dienes undergo a cycloaddition reaction ( also called pericyclic addition) with certain double bonds to afford cyclohexenes and related compounds. The simplest Diels-Alder reaction is between 1,3-butadiene and ethylene: + The formation of new carbon-carbon bonds is one of the most important aspects of synthetic organic chemistry. When a synthetic sequence calls for the formation of a ring of carbon atoms, this problem is compounded. Fortunately, the formation of six-membered carbon rings is much simpler than it would first appear. This reaction forms a six-membered ring from two pieces: a conjugated "diene" (which provides four of the ring atoms) and a "dienophile" (which provides two of the ring atoms). The main requirements for these species are that the conjugated diene must be somewhat electron rich (which is normally the case for dienes) and able to achieve the s-cis conformation , and that the " dienophile " have a two-atom ʌ system that is relatively electron poor .
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