The energy spectra of a class of 2-D polybenzenoid Clar's hydrocarbons with
a large number N(N similar to 10(4)) of carbon atoms is studied theoretica
lly. It is shown that at the asymptotic case N --> infinity the energy gap
(EG) DeltaE (N --> infinity) is different from zero, i.e.. the pi -systems
should possess semiconductor properties. The results for the EG DeltaE (N -
-> infinity) not equal 0 of the hydrocarbons are in qualitative agreement w
ith the results for the EG calculated for a class of 1-D ladder polymers ha
ving the same edge structure as the hydrocarbons. With increasing the numbe
r (M) of the pi -centers of the elementary unit of the polymers, the band g
ap DeltaE(M --> infinity) approaches also to a value different from zero. T
he quantitative results on the equilibria geometries of the hydrocarbons an
d the polymers correspond to Clar's qualitative characterization of benzeno
ids composed of disjoint "pi -sextets". The energetics of the hydrocarbons
with different types of defects and the corresponding Tamm and Frenkel stat
es were also investigated.