1 (01-23) - 1/24/2012 What is the complete mechanism of the...

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Unformatted text preview: 1/24/2012 What is the complete mechanism of the following reaction? What is the initiation step? A B C What is the complete mechanism of the following reaction? What is a propagation step? Pass your answer sheet to the course interns for 2 points toward your total of 600! A initiation B C What is the mechanism of this reaction? What is the first propagation step? A SN1 initiation propagation B SN2 C free radical 1 1/24/2012 What stops the free radical chain reaction? What reaction will terminate the free radical chain? initiation propagation i ii iii initiation propagation termination Are there any other termination reactions? A. Yes B. No initiation propagation i ii iii initiation propagation termination termination What reaction will terminate the free radical chain? Free radicals are common in biology. Which of the following drugs interferes with a biological free radical reaction? initiation i ii iii propagation A. i + ii B. i + iii C. ii + iii termination A. caffeine B. aspirin C. oxycodone 2 1/24/2012 Free radicals are common in biology. Which of the following drugs interferes with a biological free radical reaction? Why is bond at C-3 weaker than at C-1? <- 413 kJ/mol 465 -> <- 321 kJ/mol not Aspirin inhibits both COX 1 and 2 enzymes A. The C-3 bond is weaker because of increased s-character. B. The C-3 bond is weaker because the radical is stabilized by resonance. Why is 3- rather than 1-bromopenta-1,4-diene the major product? Two products are formed in this reaction. What is the other product? 465 -> <- 321 kJ/mol not + ? A B A. 3-Bromopenta-1,4-diene is more stable. B. 3-Bromopenta-1,4-diene is formed at a faster rate. C Why is 3- rather than 1-bromopenta-1,4-diene the major product? Two products are formed in this reaction. What is the other product? 465 -> <- 321 kJ/mol not energy 144 kJ/mol reaction 3 1/24/2012 Which of these two dienes is more stable? A B How can the stability of dienes be determined? H = -254 kJ/mol Is (A) more or (B) less heat going to be released when the conjugated diene is hydrogenated? Which of these two dienes is more stable? Why? 1 2 How can the stability of dienes be determined? A. Structure 2 is more stable because of inductive effects. B. Structure 2 is more stable because of electronic effects (-electron delocalization). H = -254 kJ/mol energy How can the stability of dienes be determined? How can the stability of dienes be determined? More stable by 15 kJ/mol A. Boiling points B. NMR spectra C. Thermodynamics (heats of combustion) H = -254 kJ/mol H = -239 kJ/mol energy 4 1/24/2012 What is the product of the following reaction? How could the reaction conditions be changed to favor substitution over addition? substitution rate = k[Br2] [alkene] ? addition rate = k[Br2]2[alkene] These two bromination reactions have different rate equations! A. Use low concentrations of Br2. B. Use H-Br rather than Br2. What is the product of the following reaction? How can low concentrations of Br2 be made? What is the real mechanism of bromine addition? rate = k[Br2]2[alkene] 5 ...
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