CONJUGATION IN ALKADIENES AND ALLYLIC SYSTEMS 235 10.11 The two double bonds of 2-methyl-1,3-butadiene are not equivalent, and so two different products of direct addition are possible, along with one conjugate addition product. H,C=CCH=CH, BrCH,CCH=CH, H,C=CCHCH, Br BrCH,C==CHCH, Br CH3 CH H3 3.4-Dibromo-3. 1.4-Dibromo.2. methyl-l-but (conjugate addition) 10.12 The molecular formula of the product, CIoHOCIO, is that of a 1: 1 Diels-Alder adduct between 2-chloro-1, 3-butadiene and benzoquinone H 2-Chloro-1.3. CIoHgCiO, 10.13"Unravel "the Diels-Alder adduct as described in the sample solution to part(a). H C≡N is prepared from Diels-Alder adduct (c) o is prepared from Dienophile 10.14 Two stereoisomeric Diels-Alder adducts are possible from the reaction of 1, 3-cyclopentadic methyl acrylate. In one stereoisomer the CO, CH3 group is syn to the HC=CH bridge, and is the endo isomer. In the other stereoisomer the CO, CH3 group is anti to the HC=CH bridge and called the exo isomer HC=CHCOCH H OCH Methyl acrylate Endo isomer(75%) Exo isomer (25%) ( Stereoisomeric forms of bicyclo[2. 2. 1 ]hept-5-ene-2-ca Back Forward Main Menu TOC Study Guide Toc Student OLC MHHE Website10.11 The two double bonds of 2-methyl-1,3-butadiene are not equivalent, and so two different products of direct addition are possible, along with one conjugate addition product. 10.12 The molecular formula of the product, C10H9ClO2, is that of a 1:1 Diels–Alder adduct between 2-chloro-1,3-butadiene and benzoquinone. 10.13 “Unravel” the Diels–Alder adduct as described in the sample solution to part (a). (b) (c) 10.14 Two stereoisomeric Diels–Alder adducts are possible from the reaction of 1,3-cyclopentadiene and methyl acrylate. In one stereoisomer the CO2CH3 group is syn to the bridge, and is called the endo isomer. In the other stereoisomer the CO2CH3 group is anti to the bridge and is called the exo isomer. 1,3-Cyclopentadiene O OCH3 C H Endo isomer (75%) O OCH3 C H Exo isomer (25%) (Stereoisomeric forms of methyl bicyclo[2.2.1]hept-5-ene-2-carboxylate) Methyl acrylate H2C CHCOCH3 O HC CH HC CH O is prepared from O CH O 3 Diene CH3 Dienophile O O O Diels–Alder adduct Diene C N C N is prepared from Dienophile (cyano groups are cis) H N C H N C C C O O Benzoquinone O O H H Cl Cl 2-Chloro-1,3- C10H9ClO2 butadiene 3,4-Dibromo-3- methyl-1-butene (direct addition) 3,4-Dibromo-2- methyl-1-butene (direct addition) 2-Methyl-1,3- butadiene CCH CH2 CH3 H2C Br CH3 BrCH2CCH CH2 1,4-Dibromo-2- methyl-2-butene (conjugate addition) BrCH2C CH3 CHCH2Br Br2 Br CH3 H CCHCH2Br 2C CONJUGATION IN ALKADIENES AND ALLYLIC SYSTEMS 235 Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website