CHM 501

Exam 3

December 2, 1999

1. Cyclobutadiene, shown below, is an antiaromatic molecule (that is, the electrons do not delocalize around the ring). In this problem you will construct the molecular orbital diagram for the system by considering each orbital as a group orbital on the carbon atoms. Use the axis system shown (z is perpendicular to the page) and the p_z orbitals on each carbon atom as the basis set. Find the irreducible representations of the p orbitals. Use the projection operator technique to find the wavefunctions of each of the p orbitals. Sketch each of these orbitals. Energy order the orbitals and show the electron occupation in your MO diagram.

2. TiO₂ (rutile) is a wide band gap semiconductor that can use ultraviolet light to catalyze the decomposition of water. TiO₂ has a melting point of 1843 ^oC, has a conductivity comparable to very lightly doped silicon, and is insoluble in water.