there general method to synthesize alkenes a. acidic conditions acid catalyzed dehydration of alcohols to alkene H H H H H OH 2 H H + H 2 O H H

Transcription

1 there general method to synthesize alkenes a. acidic conditions acid catalyzed dehydration of alcohols to alkene O 2 SO 4 heat O 2 SO 4 heat O 2 O 2 2 SO 4 heat + SO O + SO O + 2 SO 4 limitation; carbocation rearrangements Draw a mechanism for the following to see this. 3 3 O 2 SO 4 heat O

2 b. basic conditions dehydrohalogenation of alkyl halide to alkene 1) start with an alkyl halide 2) base 3 NaO acetone, O + Na thermodyanmic cont Sayzteff prod small and sleak hydroxide ion, O, amide ion, N 2 big and bulky potassium t-butoxide 3 + TO + Na steric control ofmann produ potassium t-butoxide, TOK 3 3 OK 3 lithium diisopropyl amide, LDA 3 3 Li N NaO acetone, potassium t-butoxide O + Na thermodyanmic cont Sayzteff prod + TO + Na steric control ofmann produ mechanism 3 O single step concert bimolecular dehydrohalogenation under basic conditions

3 c. neutral conditions dehalogenation of vincinal dihalide to alkene 1) start with an vincinal dihalide 2) this is an oxidation-reduction 3) Zn is the reducting agent and gets oxidized to Zn 2+ mechanism 3 Zn 0 single step concert bimolecular dehydrohalogenation under basic conditions a small amount of acid is added to clean the metal of its oxide coating Zn(s), + + Zn 2 zinc (II) bromide

4 Alkene Synthesis beta proton elimination (dehydrohalogenation) NaO arbene Synthesis (reactive intermediate) followed by carbene addtion to produce cyclopropane rings alpha proton elimination NaO bromoform Simmons-Smith (dehalogenation) I I Zn(s) u/ui diiodomethane Diazomethane decompostion 3 N N hv 3

5 NAME: hemistry 231 Professor: Dr. Gergens QUIZ 11A Alkene Synthesis & Reactions 1. a. Give three specific name reactions for the synthesis of alkenes. b. For each name reaction, give the appropriate reactant, conditions, and alkene product. c. For each name reaction, identify the mechanism as E1 or E2. page 5 pts Name: Mechanism: Name: Mechanism: reactant conditions alkene product reactant conditions alkene product Name: Mechanism: reactant conditions alkene product 2. Give the best reagent or set of conditions for each transformation. 3 3 a b 3 c 3 =2 3 3 O O O 3 d 3 3 O O 3 a. b. c. d. IO 4, 3. omplete the following reactions: 1.B 3 TF 2. 2 O 2,O 3 3 Pt, D 2 show correct stereochemsitry l 2 3 3,O phase transfer catalyst 4. Give the starting material needed the formation of the products under the given conditions., ROOR 3 peroxyacetic acid 2 O, + meso-2,3-butanediol

6 page 6 pts NAME: hemistry 231 Professor: Dr. Gergens QUIZ 11B 1. Identify the geometric isomerism in the following molecules A. l B. l 3. ( 3 ) ( 3 ) 3 a. ycloalkane "A" is E Z cis trans neither b. Alkene "B" is E Z cis trans neither c. Alkene "" is E Z cis trans neither 3. ircle the highest; underline the lowest (-) of hydrogenation onsider the following acid catalyzed dehydration reaction of 2-propanol. O +, O = a. alculate an overall for the above reaction using bond dissociation energies at the bottom of the page. b. Write a stepwise mechanism that shows individual steps for protonation, ionization, and elimination. c. Draw a potential energy diagram curve that depicts your overall mechanism. d. ircle the rate determining step in your potential energy diagram Bond Dissociation Energies (kcal/mole) 85 = O O Which molecules violate edt's rule:

7 NAME: hemistry 231 Professor: Dr. Gergens omplete and give the reaction name/type: O NaO acetone QUIZ 11 page 7 pts reaction name/type 3 O 3 NaN 2 acid-base rxn O 3 + (hint: any rearrangement) 2 =( 3 ) 3 2 Pt 3 potassium t-butoxide NaO acetone, 2 1.g(OAc) 2, 2 O 2.NaB 4 1.B 3 TF 2. 2 O 2,O 1 mole l cold KMnO 4 2 moles NaN 2 2.( 3 ) 3 -I hot KMnO 4 gso 4 2 SO 4 2 O

8 NAME: QUIZ 11 page 8 pts hemistry 231 Professor: Dr. Gergens Synthesis & Reactions of Propene a. Which can be made in one step from propene followed by acid work-up were appropriate? (acid work-up is not a step) b. For your choices in part a, give appropriate reaction conditions in the box below. O O l 3 O 3 = O 3 2 O 3 2 -O c. Using any a starting material three carbons or less, synthesize the remaining substances that have not yet been given reaction conditions in their corresponding box. Sythesis I Synthesis 2 Sythesis 3 Synthesis 4 Sythesis 5 Synthesis 6