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# 6 - What is the mechanism for the conversion of A to B What...

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Unformatted text preview: 2/3/2012 What is the mechanism for the conversion of A to B? What are the structures of the intermediate I, C and D? What is the structure of the intermediate I? Diels-Alder reaction A B C D What is the mechanism for the conversion of A to B? What are the structures of the intermediate I, C and D? What are the structures of C and D? Diels-Alder reaction I What is the mechanism for the conversion of A to B? What are the structures of the intermediate I, C and D? 1 2/3/2012 Why does A show an absorption at 330 nm whereas B does not? Which transition, A or B, is more probable? (i.e. the intensity of absorption) vs What are the orbitals involved in these transitions? 220 nm * 330 nm n* 224 nm, * 220 nm (A) * 330 nm (B) n* energy A B Absorptions are characterized by two properties. One is the wavelength of the maximum absorption (color). vs Are these ovals (A) the same color or (B) different colors? energy Absorptions are characterized by two properties. One is the wavelength of the maximum absorption () vs and its intensity (). absorption (A) transition = molar absoptivity () = concentration (C) x length (l) probability 220 nm * 330 nm n* 220 nm (A) * = 11,540 330 nm (B) n* = 26 energy Absorptions are characterized by two properties. One is the wavelength of the maximum absorption. vs Are these ovals (A) the same color or (B) different colors? energy Which compound, A or B, would absorb the longest wavelength of light? colorless orange 220 nm * 330 nm n* crotonaldehyde A B energy 2 2/3/2012 Two excited states are possible. Which of these is lower in energy? Why is the triplet state (T1) lower in energy than the singlet state (S1)? S1 425 nm (281 kJ/mol) light source (laser) 972 nm (123 kJ/mol) A B S0 Fluorescent dyes identifying three different cellular components of endothelial cells http://en.wikipedia.org/wiki/Fluorescence#Biochemist ry_and_medicine Why is the triplet state (T1) lower in energy than the singlet state (S1)? What is the major product of the following reaction? S1 425 nm (281 kJ/mol) T1 972 nm (123 kJ/mol) S0 Why is the triplet state (T1) lower in energy than the singlet state (S1)? What is the mechanism for its formation? S1 425 nm (281 kJ/mol) T1 972 nm (123 kJ/mol) S0 luminescence (fluorescence) 3 2/3/2012 What is the second product? + 80% ? 20% Which compound is more stable? Why? A 80% 20% B energy reaction How is it formed? + 80% 20% If A is more stable why is it not the major product of the reaction? 80% 20% energy reaction Heating the minor product of the addition reaction results in a 80% 20% small amount of the major product. If A is more stable why is it not the major product of the reaction? + 80% 20% 100% 80% 20% 100% Heating the major or minor products of the reaction results in the same reaction mixture! Why? energy reaction 4 2/3/2012 Is the activation energy for the formation of 2 greater (A) or less (B) than the formation of 1? 1 80% + 2 20% A B energy 1 reaction 2 What is the major product (A or B) if the reaction is performed at 40? A + Kinetic control. . . . . . . . . . . . -80C 80% Thermodynamic control. . . . .+40C 20% B 20% 80% energy reaction 5 ...
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