c) Draw accurate tree diagrams for the A and X signals (10 Hz = 1 cm: use a ruler!).

Transcription

1 Practice Final CEM 393 Dr..M. Muchall Name Make sure that your exam has 10 pages. Show all work. Remember: a point a minute! Textbook (Pavia, Lampman, Kriz, Vyvyan, 4 th edition) and calculator allowed. The textbook can be marked up, but pages must not have been added! 1. (13 points) The following cyclopropane gives rise to an AMX 2 pattern in its 1 NMR spectrum (400 Mz). MeO 2 C M CO 2 Me X X A X M A a) Identify the groups of signals as to their multiplicities. A: M: X: b) Determine the three coupling constants (in z) from the enlarged insets (1 ppm = 15.6 cm). Indicate on the spectrum which lines you use. J AM : cm, z J AX : cm, z J MX : cm, z c) Draw accurate tree diagrams for the A and X signals (10 z = 1 cm: use a ruler!). A: X:

2 Final Exam CEM (14 points) For the following mass spectrum, give the species from the fragmentations below. Make sure you indicate radical cations, cations or radicals where appropriate. Include the masses of all fragments in the scheme. Also include the type of fragmentation where possible. a) (6.5 points) m/z 118 m/z 103 m/z 75 b) (5 points) m/z 118 m/z 103 m/z 47 c) (6 points) An α-cleavage of the molecular ion gives rise to a metastable ion at m/z Calculate m/z for parent and daugther ions. Start with M + and show this fragmentation scheme (M + P D). Give all labels.

3 Final Exam CEM (9 points) Apart from the molar mass, what can you learn (in terms of hetereoatoms or functional groups present) from the molecular ion region of the following mass spectra? Give short (one or two keywords) answers. For each case, which is the molecular ion signal (give its m/z value)? a) additional information: a normal and a gentler ionisation method used (more gentle method) m/z: b) c) (enlarged) m/z: m/z: d) additional information: the elemental analysis shows C,, N m/z:

4 Final Exam CEM (16 points) Answer the following questions. Circle TRUE or FALSE. Give a short explanation with an example to clarify the correct or wrong statement. a) The 13 C nucleus never couples with the 1 nucleus. TRUE/FALSE b) In 1 NMR spectroscopy, at a low enough field, there are no second order spectra. TRUE/FALSE c) The coupling information in terms of multiplicity from a proton-coupled and an off-resonance protondecoupled 13 C NMR spectrum is the same. TRUE/FALSE d) 13 C NMR spectra are not integrated due to the fast relaxation of all 13 C nuclei. TRUE/FALSE e) An ethyl radical is detected at m/z 29. TRUE/FALSE f) An increase in conjugation leads to an increase in the energy required for a UV-Vis absorption. TRUE/FALSE g) The following species fragments in a Retro-Diels-Alder reaction to give a strong signal at m/z 68. TRUE/FALSE +. h) The following species undergoes a McLafferty rearrangement easily. TRUE/FALSE +.

5 Final Exam CEM (20 points) Given below is a proton-decoupled 13 C NMR spectrum. a) Starting with a base value of 2.3 ppm, calculate the 13 C chemical shift for C 1, C 2, C 3, and C 4. Use α and β corrections only up to the substituent. C 1 : C 2 : C 3 : C 4 : b) With the calculated chemical shifts and the relative intensities, on the spectrum above, label all signals with the multiplicity you would observe in a proton-coupled 13 C NMR spectrum. Ignore the TMS signal. c) Give the DEPT-135 spectrum on the line provided.

6 Final Exam CEM (12 points) The following problems have appeared in an experimental organic chemistry lab. Use the spectroscopic methods indicated for both reactant and product and explain the most important changes that you would observe in each set of spectra in order to answer the questions (you won t be able to give the answer!). Do not write full sentences, supply only the spectroscopic information (include approximate values!). a) as the elimination taken place? Ph Br Br COO KO Cl Ph Br COO UV: reactant spectrum: product spectrum: 1 -NMR: b) as the reduction taken place? O NaB 4 O 1 NMR: reactant spectrum: product spectrum: 13 C-NMR: c) Is the compound in the bottle still the desired amide, or has it become useless because all of it or just some has hydrolyzed? N hydrolysis N 2 O UV: reactant spectrum: product spectrum: IR:

7 Final Exam CEM (16 points) The 1 and 13 C NMR spectra of oxygen-containing compounds A and B (A is 100 g/mol, B 114 g/mol) are given below. Identify the two compounds. Remember that every signal carries certain information, and it should be labeled with that information. Some signals will give more detailed information than others. A A B B

8 Final Exam CEM (27 points) Identify the unknown from its data. Use all the data for your interpretation. Label all signals, and include partial structural information gained whenever possible on the spectra. Do not calculate chemical shifts. Work not shown will not get you points. elemental analysis: 87.3 % C, 12.7 %

9 Final Exam CEM Use the mass spectrum to confirm the structure you determined above: comment on the absence of the molecular ion peak and explain all numbered peaks as fragments from M (include masses, charges, radicals).

10 Final Exam CEM Additional space for Q 8. Good luck.