Abstract:
The bonding patterns in coronene are complicated and controversial. Among the
different proposed descriptions, the two most representative are those generated by
Clar's aromatic π-sextet and Adaptative Natural Density Partitioning (AdNDP)
models. The chapter 1 reports the detailed quantum-chemical calculations at the
density functional theory level to evaluate the model that gives a better
representation of coronene. In addition, the analysis of the molecular structure of
coronene, quantification of the aromaticity using various local aromaticity descriptors
and assessment of the Diels-Alder reactivity with cyclopentadiene have been carried
out. It has been concluded that Clar's π-sextet model provides the representation of
coronene that better describes the physicochemical behaviour of this molecule.
The recent studies show that properties of coronene could be tuned by
isoelectronic substitution procedures. Thus, the effect of single, double and triple BN
pair substitution on the aromaticity and stability of coronene is investigated in
Chapter 2. The nucleus-independent chemical shift (NICS)-based method, has been
used for its aromaticity assessment. The study reveals that the positional isomers
with adjacently placed BN units are the most stable structure. Charge separation and
different bond strength together play an important role in rationalizing the relative
stability trends. The aromatic character of all BN substituted rings decreases w.r.t
unsubstituted coronene except in case of triple BN pair substitution in inner ring,
where the NICSzz(1) values of outer rings increase. It is found that depending upon
the position of BN pairs, the HOMO-LUMO gap of coronene could be modulated.
Thus, it is proposed to study the opto-electronic properties of these molecules.
