Abstract. You will optimize the structures of a
number of cyclic, conjugated ketones. You will then examine the bond lengths
and bond orders of the ketones, in order to look for effects of aromatic
resonance contributions.
Procedure. Build and optimize the following cyclic
ketones using a semiempirical method. Record the C=O bond lengths and orders,
and the Mulliken charges on the C=O bond. If you have time, you may optionally
compute the IR spectrum of each of these molecules (takes considerable time!).
Use resonance arguments to try to explain the trends.
Benchmarks. Comparative experimental
C=O stretching frequencies are given below where available. Do these correlate
with your computed results above?
