Chapter 14 Conjugation, Res 682 o gributonal PROBLEMS Problems Using Three-Dimensional Models 14.31 Name each diene and state whether the ball-and-stick model shows the diene in the s-cis or s-trans conformation. b. a. uboy Dubend al oubon 13ubong olme 14.32 What diene and dienophile are needed to prepare each compound by a Diels-Alder reaction? mer d on on b. a. th th dand piios ala-a era of Conjugation 14.33 Which of the following systems are conjugated? See Sem CN b. d. a. C. ansib-E.P Lo0 diene (1410 ducts Resonance and Hybridization uclecphtic oaw is-products renulng sttack at the positve charge of beth ress bioendib dres fostiriqo nco stre 14.34 Draw all reasonable resonance structures for each species. res. ce :0: boheonon ai melnera erT bno ge Ӧн f. b. O slpnlen :0: :0: a. d. C. e. 14.35 For which compounds can a second resonance structure be drawn? Draw an additional resonance structure and the hybrid for each resonance-stabilized compound. 1-ale ОCHЗ noib a. bns orisib prd b. NHCH3 beadmanxiz orts vinebl C. d. bnod e 'N' CHз ОСКЗ ort rlive 14.36 Draw all reasonable resonance structures for each compound. Z isor :0: allylic co: lon a. b. one NH2 NH2 C. d. N. b anel 14.37 Explain why the cyclopentadienide anion A gives only one signal in its 1°C NMR spectrum. 15 Try roblems 14.43b, c14.6 14.38 Why is the bond dissociation energy for the C-C bond in ethane much higher than the bond dissociation energy for the labeled C-C bond in but-1-ene? CH3-CH3 ethane but-1-ene +368 kJ/mol +301 kJ/mol :O: Problems 683 Nomenclature and Stereoisomers in Conjugated Dienes 14.39 Draw the structure of each compound. a. (Z)-penta-1,3-diene in the s-trans conformation b. (2E,4Z)-1-bromo-3-methylhexa-2,4-diene C. (2E,4E,6E)-octa-2,4,6-triene d. (2E,4E)-3-methylhexa-2,4-diene in the s-cis conformation 4O Name each compound and indicate the conformation around the o bond that joins the two double bonds. a. b. 14.41 Label each pair of compounds as stereoisomers, conformations, or constitutional isomers: (a) A and B; (b) A and C; (c) A and D; (d) C and D. A B 14.42 Rank the following dienes in order of increasing heat of hydrogenation. Electrophilic Addition 00 0geg of boboen us olingoneib bs en 14.43 Draw the products formed when each compound is treated with one equivalent of HBr. b. C. 14.44 Ignoring stereoisomers, draw all products that form by addition of HBr to (E)-hexa-1,3,5-triene. 14.45 Treatment of alkenes A and B with HBr gives the same alkyl halide C. Draw a mechanism for each reaction, including all reasonable resonance structures for any intermediate. Br HBr HBr 14.46 Draw a stepwise mechanism for the following reaction. Br. Br HBr ROOR bouogmos noitpeoebIA 14.47 Addition of HCI to alkene X forms two alkyl halides Y and Z. exocyclic C=C HCI TCI a. Label Y and Z as a 1,2-addition product or a 1,4-addition product. b. Label Y and Z as the kinetic or thermodynamic product and explain why. C. Explain why addition of HCl occurs at the indicated C=C (called an exocyclic double bond), rather than the other C=C (called an endocyclic double bond). a.