Question

I. Conjugated dienes undergo Diels-Alder reaction and form 6-membered rings. In order for this reaction to occur, the diene must be in the S-cis conformation and an alkene (dienophile) preferably with an electron-withdrawing group. EW EW U +U Diene S-cis conformation Dienophile racemic product Indicate which of the following compounds can function as the diene in Diels- Alder reaction and why: Cli) The rates of Diels-Alder reaction of the compounds below are compare with that of 1,3butadiene. Please explain the trend. CHE H3C CH, CHE H H CH, similar to butadiene faster Slower increasing stabilt uf sucis contes Ditid alde reach increarry Page of undugung wtoring rachun rul 4 of 4

Answer 1

Page No. Date As we all know for Diels-Aldex reactiorube of diene S-cis conformation is mandatory. so that cene which has undergo Diels-Alder reach s. cis conformation are readily In your given example, Cyclopentadiene is in S-cis conformation so acts as diene in Diels -Alder reach Other diens are having s-trans conformation Let's see what is mean by socis and s-trans. * Gr & - Elue See through the single bond & predict first which is c3 & trans. & then write them as socis & sotrans , s 3 for the single bond. donated CH3 CHA CH3 CH3 faster Slow er Similar to butadiene

Structural reature that aid or hinder the diene in achieving socis conformation affects Ptg ability to participate in the Diels-Alder reach. Thus the diene with Hunctional groups that hinder the s-cis conformation reacts slower than butadiene . Dieng with functional groups that hinder the grans conformation reacts faster than butadiene So, CM Here, the two -CH groups hindered the socis conformation, so reacts. slower, Here -CH₂ groups neither hindered the socis nor s-trans conformation so reacts game as butadiene. CH₂ cry Here, -Cha groups hindered the s-trans conformation so reacts. faster than butadiene Here, in cyclic system (5 memb) the s-trans conformation is not possible so it reacto much faster than butacliene