CHAPTER 8 HW: ELIMINATIONS REACTIONS

Transcription

1 APTER 8 W: ELMNATNS REATNS S-TRANS SMERSM 1. Use a discussion and drawing of orbitals to help explain why it is generally easy to rotate around single bonds at room temperature, while it is difficult to rotate around double bonds. 2. Which of the following compounds can exist as cis and trans isomers? When this type of isomerism is possible, draw the other isomer (if trans is shown, draw cis). 3. raw all isomers of 2 2, including stereoisomers. Page 1

2 4. dentify the relationship between each pair of compounds. Are they identical, constitutional isomers, or stereoisomers? Pair Relationship Pair Relationship Pair 3 3 Relationship ALKENE STABLTY 5. Answer the questions while using the following enthalpy dat (kcal/mol) 2 Pd 2 Pd Use the data to determine the relative stability of 1-butene compared to cis-2-butene. Explain how you used the enthalpy dat Would you expect a similar reaction of trans-2-butene to release more or less than cis-2- butene? iefly explain. Page 2

3 6. Answer the questions about the following alkenes. Rank the following alkenes from low to high energy. Explain the tren Which alkene would you expect to release the least amount of upon combustion? Explain. E2 REATNS: MEANSMS + TRANSTN STATES 7. raw the curved arrow mechanism for these E2 reactions, including all lone pairs and charge. nclude any missing products. Na K 3 Page 3

4 8. raw the energy diagram for this E2 reaction, including the structure of the transition state For each E2 reaction, give the products then draw the E2 transition state. - K 10. raw all possible elimination products for the following reactions, including stereoisomers. ecide which should be the major elimination product and briefly explain why. Na( 3 ) 3 K 3 Na K( 3 ) 3 Page 4

5 E2 REATNS: SUMMARY F FATRS 11. n each pair of reactions, decide which will be a faster E2 reaction. Explain. Na Na Na 2 Na Na Na 2 Na MS 12. When Na 3 is used as the base in the following reaction, the major product is M. When Na( 3 ) 3 is used as the base, the major product is N. Explain these different results. base M + N Page 5

6 E2 REATNS: ANT ELMNATN 13. Which should be the major product (J-M) of this E2 reaction? Explain, including Newman projections with your answer. K J K L M 14. nly one product is observed in reaction (1) while a mixture is formed in reaction (2). Use chair conformations to explain why only one product is formed in reaction (1). Na 2 3 (1) 100% 2 3 (2) Na major Use chair conformations to explain why two products are formed in reaction (2), then why one product is the major. Page 6

7 15. Give the major organic product for these E2 reactions. Keep in mind that the b -hydrogen must be anti to the leaving group in an E2 reaction. Na 3 f. Na K g. Na 3 Na 3 3 h. K 3 Na i. 3 Na e. K j. Na 3 E1 REATNS: MEANSMS + TRANSTN STATES 16. Give the curved arrow mechanism for these E1 reactions. 3 high (major product is still S N 1, but E1 competes significantly) Page 7

8 17. raw the energy diagram for this reaction, including the structure of the transition state for the rate determining step. 2 E1 REATNS: SUMMARY F FATRS 18. n each pair of reactions, decide which should have a faster E1 reaction and explain. (Note: in some reactions E1 is not the major pathway, but still decide if an E1 were to occur, which would be faster.) S Na 2, /MS Page 8

9 E1 VERSUS E2 REATNS 19. For each elimination reaction, decide whether it proceeds through an E1 or E2 mechanism. Then give the major product and draw the appropriate curved arrow mechanism. Reaction E1/ E2? Major Product Mechanism Na Na( 3 ) 3 2 high 3 ELMNATN VERSUS SUBSTTUTN REATNS 20. Explain why the amount of elimination product (relative to substitution product) increases when the of the reaction is increase Page 9

10 21. Should compound A or compound B be expected to react faster in each mechanism? iefly explain. A B S N 2 S N 1 E2 E1 22. Which of reactions A- should never proceed through an E1 or S N 1 mechanism (there may be >1 correct answer)? Explain why these reactions should not react through these mechanisms. A B Na Substitution and elimination reactions always compete with each other. For each reaction below, draw the probable substitution and elimination products, considering if a 1 st or 2 nd order mechanism is likely. Then identify the major product. 2 3 K MF NaN acetone Page 10

11 24. Explain why reaction 1 and 2 produce different alkenes as their major products. Na 3 3 Reaction 1 Reaction For each reaction, decide whether the major pathway should be S N 1, S N 2, E1, or E2. Then give the appropriate curved arrow mechanism that produces the major product for each. Mechanism and Major Product S N 1, S N 2, E1, E2? 3 Na high S 2 F 3 NaS Page 11

12 26. Give the major organic product for each reaction. Pay attention to stereochemistry and if a mixture of products is expected (i.e. racemic mixture), draw all products. dentify if the reaction mechanism is S N 1, S N 2, E1, or E2. 3 j. 3 K 2 3 k NaN 2 l. K acetone S 2 F 3 2 high m. ( 3 ) 3 Na e. KS MS n. 3 K f. Na MF o. NaN 3 3 N g. Na p. K acetone h. 3 Na q. K acetone 3 i. S KN r. F excess 3 N - Page 12