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Chemistry Lab Experiments: Friedel-Crafts, GC, and NBS Bromination

Explore lab experiments on Friedel-Crafts reactions, Gas Chromatography, and NBS Bromination. Learn reaction mechanisms, carbocation intermediates, GC peaks, theoretical yield calculations, radical reactions, and synthesis of Bromoethylbenzene. Discover the roles of N-Bromosuccinimide and dibenzoyl peroxide in reactions, as well as the significance of solvents like CCl4. Prepare for upcoming topics on NMR and Diels-Alder reactions in the lab.

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Chemistry Lab Experiments: Friedel-Crafts, GC, and NBS Bromination

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  1. Today: Conclusion of Friedel-Crafts/GC Introduction to NBS-Bromination (Exp. 3) MiniQuiz

  2. Friedel-Crafts Alkylations (Exp.II) Reaction equation for the reaction of p-xylene with 1-bromopropane in the presence of aluminum trichloride (our lab experiment): Mechanism… : Which carbocation intermediates are formed?

  3. Friedel-Crafts Alkylations • Which of the following Friedel-Crafts reactions would you expect to work well, which ones not at all and why? • a) Toluene reacting with chloromethane in the presence of aluminum chloride catalyst • b) Toluene reacting with chlorobenzene in the presence of aluminum chloride catalyst • c) Benzaldehyde reacting with chloromethane in the presence of aluminum chloride catalyst

  4. Gas Chromatography • Which is the moving phase, which is the stationary phase in our GC? • What peaks do you expect to get in your GC of Exp.II? What determines their approximate sequence? • What is a mole ratio? And what is a mole fraction?

  5. II.Weight of product mixture What is in product mixture? Percent by weight of mono n-propyl product in product mixtureWeight fraction… Remember: Different molecular weights… Theoretical yield in grams of mono n-propyl product Balanced equation (assuming that only mono n-propyl product is formed), mols, mol ratios … Percent yield mono n-propyl product* [Actual yield / theor. Yield] x % Ratio of n-propyl to isopropyl product* GC!Area ratio =mol ratio Calculations for Friedel-Crafts Experiment 3. 1. 4. 2.

  6. Synthesis of Bromoethylbenzene; H-NMR (Manual Exp.III) What is the structure of N-Bromosuccinimide (NBS)? What type of a reaction is this? • What is a “radical” in chemistry? • What is the geometry of a carbon radical? • What reaction conditions generally tend to lead to radical intermediates? • What are the major steps found in every radicalreaction?

  7. Synthesis of Bromoethylbenzene; H-NMR (Manual Exp.III) • Why does bromination in our reaction occur at the α-position only? • What is the function of NBS? • What is the function of dibenzoyl peroxide?

  8. Propagation How can you explain that the reaction mixture goes through a series of color changes?

  9. Synthesis of Bromoethylbenzene (Manual Exp.III) • Properties of CCl4? • Why is CCl4 a good solvent for our reaction mixture? • What are criteria for a "good solvent" in general? • What is the purpose of addingcyclododecane?

  10. Next time: • NMR (Concl. of Exp.3) • Introduction to Diels-Alder (Exp.4) • MiniQuiz on this lecture

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