final-sample-s16

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McGill University *

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293

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Chemistry

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Jan 9, 2024

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pdf

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10

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CHEM 293 ________________________ Sample Final Name Dr. H.M. Muchall Make sure that your exam has 10 pages. Show all work. Remember: a point a minute! Textbook 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 A 2 MX pattern in its 1 H NMR spectrum (400 MHz). a) Identify the groups of signals as to their multiplicities. A: M: X: b) Determine the three coupling constants (in Hz) from the enlarged insets (1 ppm = 15.6 cm). Indicate on the spectrum which lines you use. J AM : cm, Hz J AX : cm, Hz J MX : cm, Hz c) Draw accurate tree diagrams for the A and X signals (10 Hz = 1 cm: use a ruler!). A: X: A A M X H H H H MeO 2 C CO 2 Me A M X
CHEM 293 Final Exam 2 2. (11.5 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
CHEM 293 Final Exam 3 3. (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) m/z: b) c) m/z: d) m/z: (more gentle method) additional information: a normal and a gentler ionisation method used (enlarged) additional information: the elemental analysis shows C, H, N m/z:
CHEM 293 Final Exam 4 4. (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 H nucleus. TRUE/FALSE b) In 1 H 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 proton- decoupled 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-type rearrangement easily. TRUE/FALSE + . + .
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