chapter 7

chapter 7 - Chapter 7 - 1 Chapter 7. Alkenes and Alkynes I:...

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Unformatted text preview: Chapter 7 - 1 Chapter 7. Alkenes and Alkynes I: Properties and Synthesis Elimination Reactions of Alkyl Halides Using CIP convention, determine priorities on each alkene atom. 7.2. The ( E )-( Z ) System for Designating Alkene Diastereomers ( E ) is like trans , and ( Z ) is like cis . C C H H 3 C H CH 3 cis (Z) C C CH 3 H 3 C H H trans (E) When there are identical groups, you can use cis and trans . E and Z are better terms in general. C C D A C B (Z) C C B A C D (E) Assuming in priorities A > C B > D A, B on the same side A, B on the opposite sides Chapter 7 - 2 For example, C C F Br H Cl (Z) C C Br Cl H Cl (E) higher lower higher lower higher lower lower higher 7.3. Relative Stabilities of Alkenes More substituted alkenes > less substituted alkenes Trans alkenes > cis alkenes Why is trans more stable than cis? C C C C steric no steric However, cycloalkenes: cis > trans only cis Trans is not possible because it is too strained. Chapter 7 - 3 Question) How can one make alkenes? 7.6. Dehydrohalogenation of Alkyl Halides R X base R 7.6A, 7.6B. Zaitsev's rule ---> Form more stable, more substituted alkenes if a small base is used. Hofmann rule ---> Form less substituted alkenes (anti Zaitsev's rule) if a bulky base is used. Br H H H NaOEt major product (more substituted) NaO t Bu major product (less substituted) B B Chapter 7 - 4 Why different results on different bases?...
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chapter 7 - Chapter 7 - 1 Chapter 7. Alkenes and Alkynes I:...

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