Practice Test III.Vibrational, UV/Vis, and NMR spectroscopy. E. Korobkova
Problem 1.The frequency of the O – H stretching vibration in CH3OH is 3300cm-1. Estimate the frequency of the O – D stretching vibration in CH3OD.
Problem 2. Arrange the following groups in order of increases the chemical shift of a proton:
a)CH3Cl
b)CH2Cl2
c)– OH
d)– COOH
e)CH4
f)C(CH3)3
TRUE OR FALSE (3-5)
3. In Molecular Orbital Theory electronic orbitals are considered separately for different atoms.
4. NMR spectra belong to Radio Wave region.
5. According to a Born-Oppehngeimer approximation, nuclei move much faster than electrons.
Problem 6. Arrange the following molecular groups in order of increases fundamental vibrational wavenumber (frequency).
Problem 7.
Match the following three molecules with their respective NMR spectra:
Problem 8. Calculate the number of vibrational modes in toluene.
Problem 9. Sketch an NMR spectrum for a molecule shown below:
Problem 10. Calculate a g-factor of 14N if its magnetogyric ratio is 1.9331×107 T-1s-1.
Problem 11. Using a 1H NMR spectrum below, propose a structure for the compound with an empirical formula C4H8O2. Integrated intensities are shown in parentheses. Assign each hydrogen atom to its line in the spectrum.
Problem 12. Calculate the NMR resonance frequency for a19F atom if Bloc = 10.5 T.
Problem 13. Determine the wavenumber of the overtone v=0 → v=3 in HF molecule if the fundamental vibrational wavenumber is 4141.03 cm-1, xe = 0.021840 and ye = 0.00028447, where xe and ye are first and second anharmonicity constants, respectively.
Problem 14.What is the total spin in the ground state configuration of (a) fluorine molecule, O2; (b) nitrogen molecule, N2?
Problem 15.What is the highest occupied molecular orbital in N2 molecule? Calculate the bond order of the molecule.
Problem 16.Compose a secular determinant in Huckel approximation for the following p-conjugated system:
Problem 17. Using the energy diagram below, estimate the ratio of the phosphorescence and fluorescence rates in tryptophan (W) molecule.
Problem 18. Sketch an NMR spectrum for an aspirin molecule:
Problem 19. Using the following set of vibrational wavenumbers observed in an IR spectrum, proposemolecular structure:
C10H8O
1600 cm-1
1680 cm-1
2910 cm-1
1420 cm-1
1380 cm-1
2200 cm-1
815 cm-1
Problem 20. Arrange in order of increasing absorption wavenumber the following vibrational modes. Explain.
Problem 21. Assign transitions in a UV/Vis spectrum of tetracyclone:
Problem 22. Assign transitions in a UV/Vis spectrum of the following molecule:
True or false (23-31):
23. Fluorescence arises from the decay of the excited single state S1 to the ground state S0.
24. Phosphorescence arises from the decay of the excited triplet state T1 to the ground state S0.
25. Phosphorescence is allowed by quantum mechanical rules.
26. Franck–Condon principle is the approximation that an electronic transition is most likely to occur without changes in the positions of the nuclei in the molecular entity and its environment.
27. A harmonic oscillator model provides the exact description of the vibrational motion of diatomic molecules.
28. Morse potential includes the effect of bond breaking.
29. The number of vibrational states in Morse potential is infinite.
30. In a harmonic oscillator model, the selection rule is Δv = ±2.
31. Overtones are not allowed in a Morse potential model.
Problem 32. Name transitions indicated on the following scheme.
Problem 33.
Which of the following compounds are likely to exhibit LMCT and MLCT transitions?
MnO4−
CrO42−
VO43−