Bonding in Polycyclic Aromatic Hydrocarbons
Methodology
Molecular Mechanics (Force Field)
Techniques Used
Building, Optimization, Analysis of Bonding Parameters, Output Analysis
Abstract. One definition of aromaticity may be
supported by the presence of delocalized bonding in a pi-network. You can
check this by optimizing the geometries of a variety of polycyclic aromatic
hydrocarbons, using force field methods. You will then search for aromatic
portions of the molecule based on delocalized bond lengths, as well as for
possible superaromatic geometries (extensive delocalized systems).
Procedure. Build and optimize the following polycyclic
aromatic hydrocarbons (PAHs). In the results table, record the bond lengths
of various bonds around each ring. Can you find evidence for dominance of
benzenoid rings (the Clar sextet rule)? Can you find evidence for localized
double bonds, which should be unusually reactive? Can you find evidence
for superaromaticity through extensive delocalization of the pi-bonds?
Copyright 1995 by Paul M. Lahti. All Rights
Reserved.