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Synthesis of Unsaturated Hydrocarbons: Problem Solving with Alkynes and Alkenes

Dive into complex organic chemistry problems involving alkynes and alkenes, exploring reactions, mechanisms, and synthesis pathways. Understand the roles of catalysts and functional groups in multistep syntheses. Practice retrosynthetic analysis to solve a challenging problem involving an unknown compound and its transformations.

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Synthesis of Unsaturated Hydrocarbons: Problem Solving with Alkynes and Alkenes

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  1. Alkynes Reaction Acidity Synthesis

  2. s-Complex of Acetylene p-Bonds

  3. Hydrocarbon Comparison

  4. Alkyne Nomenclature

  5. Enes with Ynes

  6. Endiyne Antitumor Agents

  7. Catalytic Hydrogenation

  8. Lindlar’s Catalyst

  9. H2 on a Poisoned CatalystPrevents Over-Reductioncis Alkenes

  10. Dissolved Lithium in NH3trans Alkenes

  11. Addition of HX

  12. Br2 Addition

  13. Oxymercuration HydrationMarkovnikov

  14. Enol – Keto TautomerizationIntermolecular

  15. Oxymercuration Mechanism

  16. Hydroboration HydrationAnti-Markovnikov

  17. Hydroboration Mechanism

  18. Draw the Products

  19. Ozonolysis

  20. Acidity of Terminal Alkynes

  21. Acetylide Formation

  22. Alkylation of Acetylide IonsHomologations using SN2 rxn

  23. Multi-step Syntheses

  24. Retrosynthetic AnalysisBegin with the Product

  25. Fill in the Reagents

  26. How Many Steps?

  27. 5 Steps

  28. Nucleophilic Addition

  29. Acetylide Addition to Ketones and Aldehydes

  30. Nucleophilic addition to Benzaldehyde

  31. Synthesis Problem

  32. Six separate steps(each individual reaction is denoted with a number)

  33. An unknown compound (A) has a formula of C11H14. Treatment of A with H2/Pd-carbon gives B (C11H20). Treatment of A with H2 on a Lindlar catalyst gives C (C11H16). Ozonolysis of C followed by workup with Zn, HOAc affords formaldehyde and the tricarbonyl compound shown below.

  34. Schematic of the Problem

  35. An initial approach to this problem is to determine the number of degrees of unsaturation in each of the molecules A,B,andC. When A (C11H14, 5o unsat.) is hydrogrenated, B (C11H20, 2o unsat.) is formed. That means that 3 p bonds reacted (3 mol. equivalents) to form B. When A is treated with H2 over a Lindlar (poisoned) catalyst, 1 mol equiv. of H2 reacts. Since this reaction is specific for the reduction of alkynes to alkenes, 2 of the 3 p bonds in A are in the form of a triple bond. The remaining p bond must be an alkene. We have accounted for three of the five degrees of unsaturation in A, therefore the other two must be rings since they do not react with H2.

  36. Propose Structures for A, B, and C

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