09-20 - 9/21/2010 What infrared absorption would be...

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Unformatted text preview: 9/21/2010 What infrared absorption would be predicted for the C=O group of 2-butenone? A. 1686 cm-1 B. 1728 cm-1 2-butenone C=O = ???? cm-1 Molecules have many different vibrational possibilities. butanone C=O = 1710 cm-1 O O How do the resonance structures of these two compounds differ? O 1 2 How many vibrational modes are possible? 3n-6 = number of vibrational modes n = number of atoms in a molecule How many vibrational modes would be predicted for formaldehyde (CH2=O)? A. 3 B. 6 C. 8 D. 20 E. 32 F. >32 3n-6 = number of vibrational modes 3n-6 = 3(4) – 6 = 6 3 4 Any molecule has 3n-6 vibrational modes where n = number of atoms present in the molecule. How many vibrational modes would be predicted for ibuprofen? OH 1750 cm-1 1165 cm-1 C13H18O2 O ibuprofen = 3n – 6 = 3(33) – 6 = 93 vibrational modes A. 3 B. 6 C. 8 D. 20 E. 32 F. >32 6 1 9/21/2010 Which functional group in ibuprofen is responsible for the strong absorption at 1721 cm-1? ΞC-H C-H =C-H O-H CO2H CΞC C=C C=O N-H CΞN 3000 A. C-H C- B. C=O C. C=C D. O-H O- E. C-C C- 4000 A. C-H B. C=O 2000 C. C=C cm-1 1500 D. O-H 1000 E. C-C 600 OH O O OH * 7 * 8 Why is the C=O bond stretch the most intense? + = hν Why is the C=O bond stretch the most intense? + hν = hν v=0 v=1 OH O O OH Why is the C=O bond stretch the most intense? + δ δ v=0 hν δ v=1 4000 = hν δ ΞC-H -C-H =C-H O-H CO2H CΞC C=C C=O orgchem web site N-H 3000 CΞN 2000 cm-1 1500 1000 600 A. A. The oxygen and carbon are the heaviest atoms. B. This vibration represents the largest change in dipole moment. C. The C=O bond is the strongest. O OH 2 9/21/2010 13 14 Do all C-H bonds have the same strength? CCΞC C-H p -C-H =C-H ΞC-H s energy C=C high energy 4000 3000 2000 cm-1 1500 1000 low energy 600 Which of the following has the C-H bonds correctly assigned to the above infrared absorptions: , and ? A. C. E. ΞC-H -C-H =C-H =C-H ΞC-H -C-H -C-H =C-H ΞC-H B. D. F. ΞC-H -C-H =C-H -C-H =C-H ΞC-H =C-H ΞC-H -C-H Csp—H1s A. Csp2—H1s Csp3—H1s ΞC-H =C-H -C-H increasing strength of the C-H bond C- CΞC C-H C=C ΞC-H -C-H =C-H O-H CO2H CΞC C=C C=O N-H 4000 3000 2000 cm-1 1500 1000 600 4000 3000 CΞN 2000 cm-1 1500 1000 600 Which of the following has the C-H bonds correctly assigned to the above infrared absorptions: , and ? A. C. E. ΞC-H -C-H =C-H =C-H ΞC-H -C-H -C-H =C-H ΞC-H B. D. F. ΞC-H -C-H =C-H -C-H =C-H ΞC-H =C-H ΞC-H -C-H A. ΞC-H =C-H -C-H 3 9/21/2010 ΞC-H -C-H =C-H O-H (s) CO2H CΞC C=C ΞC-H -C-H =C-H CΞC C=C C=O(s) N-H 4000 3000 CΞN 2000 cm-1 Which structure is consistent with the following ir spectrum? 1000 600 4000 O-H CO2H C=O N-H 3000 O OH O OH CH3 CΞN 2000 cm-1 Which structure is consistent with the following ir spectrum? 1500 1000 600 1500 C=O overtone ? ? O OCH3 O O OH A OCH3 O D OH O OH OH OH O A B C D B OCH3 C OCH3 ΞC-H -C-H =C-H O-H CO2H CΞC C=C ΞC-H -C-H =C-H CΞC C=C C=O N-H 4000 3000 CΞN 2000 O CH3 O O OH Which structure is consistent with the ir spectrum? 1500 1000 600 4000 O-H CO2H C=O N-H 3000 CΞN 2000 cm-1 Which structure is consistent with the ir spectrum? 1500 1000 600 cm-1 OH O OH CH3 O O O OH OH O OH D OH O A OCH3 O OCH3 O OCH3 A OH OCH3 O OCH3 D B C OCH3 B C Why Communicating Science Matters: A conversation between Alan Alda and Brian Greene Thursday, September 23, 2010 4:00pm to 5:00pm Staller Center Auditorium- Free and open to the public 4 ...
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