11. a. How many lines would you expect in the spectrum of the hypothetical molecule SCI, (I for S = 0 and Cl = )? b. Using a procedure similar to that in Fig. 9-6 and Fig. 9-7, explain how this number arises and indicate the transitions with arrows. State what the expected relative intensities would be.
Formal Charges
Formal charges have an important role in organic chemistry since this concept helps us to know whether an atom in a molecule is neutral/bears a positive or negative charge. Even if some molecules are neutral, the atoms within that molecule need not be neutral atoms.
Polarity Of Water
In simple chemical terms, polarity refers to the separation of charges in a chemical species leading into formation of two polar ends which are positively charged end and negatively charged end. Polarity in any molecule occurs due to the differences in the electronegativities of the bonded atoms. Water, as we all know has two hydrogen atoms bonded to an oxygen atom. As oxygen is more electronegative than hydrogen thus, there exists polarity in the bonds which is why water is known as a polar solvent.
Valence Bond Theory Vbt
Valence bond theory (VBT) in simple terms explains how individual atomic orbitals with an unpaired electron each, come close to each other and overlap to form a molecular orbital giving a covalent bond. It gives a quantum mechanical approach to the formation of covalent bonds with the help of wavefunctions using attractive and repulsive energies when two atoms are brought from infinity to their internuclear distance.
Spectroscopy Drago book, second edition, chapter 9 electron paramagnetic resonance, page no 403 ques 11
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indicate electron delocalization onto the oxygen?
c. The magnitude of a in this material is 2.37 gauss. Compare the spin density on
hydrogen in this molecule with that on a hydrogen atom.
d. How would the sign of the proton hyperfine coupling constant indicate whether
the odd electron was in a sigma- or pi-molecular orbital?
e. Using the value of a, given above and the fact that the unpaired electron is in the
T-system, calculate the spin density on the nearest neighbor carbon.
6. The 1C hyperfine coupling in the methyl radical is 41 gauss, and the proton hyperfine
coupling is 23 gauss. Sketch the spectrum expected for 13.CH, radical. [For answer,
see T. Cole et al., Mol. Phys., 1, 406 (1958).]
7. Assume that all hyperfine lines can be resolved and sketch the spectrum for the
chlorobenzene anion radical.
8. Assuming all other factors constant, would line broadening be greater for a bimolecular
process with a rate constant of 10' or with a rate constant of 1010?
9. How many lines would you expect in the epr spectrum of (CN),CoO,Co(NH,),?
Explain.
10. The spectrum below is obtained for the NH,radical:
a. Convert it to an absorption spectrum.
b. How could you determine whether the larger or smaller splitting is due to hydrogen?
c. Assume that the larger splitting is due to nitrogen. Construct a diagram similar to
Fig. 9-10 to explain the spectrum.
Exercises
403
11. a. How many lines would you expect in the spectrum of the hypothetical molecule
SCI, (I for S = 0 and Cl = )?
b. Using a procedure similar to that in Fig. 9-6 and Fig. 9–7, explain how this number
arises and indicate the transitions with arrows. State what the expected relative
intensities would be.
12. The epr spectrum of the cyclopentadiene radical (C,H,) rapidly rotating in a single
crystal of cyclopentadiene is given below.
30 G
a. Write the appropriate spin Hamiltonian.
b. Interpret the spectrum.
13. Interpret the epr spectrum of •CH,OH given below.
404
Chapter 9
Electron Paramagnetic Resonance Spectroscopy
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