All references are to articles from J. Am. Chem. Soc., 2001, 123. The exam is open book and open notes.
1. N. Burford, T. S. Cameron, P. J. Ragogna, E. Ocando-Mavarez, M. Gee, R. McDonald, and R. E. Wasylishen (pages 7947-7948) synthesized some phosphinophosphonium salts. One of these was [Ph3P-PPh2][CF3SO3] (Ph = phenyl). Write the Lewis structure for each ion (treat the phenyl group just as Ph), show the formal charges and oxidation numbers for each P and S, and predict the geometry for each ion (including estimates of bond angles). Estimate the pKa of CF3SO3H using Pauling's rules. Comment on the reliability of this estimate.
2. A. Gapeev and R. C. Dunbar (pages 8360-8365) studied cation-pi interactions. Why should cations bond to pi systems? Using equilibrium measurements and some literature data, they reported the following data:
Pyr(g) + Na+(g)
[NaPyr]+(g)
G = –138 kJ/mol
A(g) + [NaPyr]+(g)
AME(g) + [NaPyr]+(g)
A(g) + [NaAME]+(g)
PA(g) + [NaAME]+(g)
Here, A = alanine, PA = phenylalanine, AME = alanine methylester, and Pyr = pryidine. Use this data and appropriate Born-Haber cycles to find the reaction free energies for the following reactions. Use this information to estimate the size of the cation-pi interaction.
A(g) + Na+(g)
PA(g) + Na+(g)
3. L. Khriachtchev, M. Pettersson, A. Lignell, and M. Räsänen (pages 8610-8611) studied the photochemical reaction of HF in an Ar matrix and found spectroscopic evidence for HArF. Write the Lewis structure for HArF, determine the structure, indicate the likely sigma hybrization about the Ar atom, and give the point group of the molecule.
4. J. L. C. Rowsell, V. Pralong, and L. F. Nazar (pages 8598-8599) looked at some intercalation chemistry of lithium nitride. Estimate the lattice energy for lithium nitride, which crystallizes in the antifluorite structure. (The Madelung constants for the fluorite and antifluorite structures are the same.)
5. S. V. Rosokha and J. K. Kochi (pages 8985-8999) investigated the electron transfer reaction between NO+ and aromatic hydrocarbons. They found that the reaction proceeds by an inner sphere mechanism. Using benzene as an example, suggest a structure for the transition state complex.
6. A. C. Bean, C. F. Campana, O. Kwon, and T. E. Albrect-Schmitt (pages 8806-8810) isolated a silver uranyl compound containing the IO43– ion. Find the point group for this ion.
7. A. E. Kuznetsov, A. I. Boldyrev, X. Li, and L.-S. Wang (pages 8825-8837) created Ga42– in the gas phase and claim that the ion is aromatic. Construct the MO diagram for the pi electrons using group theoretical methods.