Chemistry Reference
In-Depth Information
The resulting bandgap is zero (when curvature variations of the Hückel parameters
are neglected) so that the nanotube will have a metallic conductivity, and otherwise
it will behave as a semiconductor. As a result, all armchair SWNTs and one-third
of zigzag and chiral SWNTs are metallic, whereas two-thirds are semiconducting
(Klein and Balaban
2011
).
1.8
Concluding Remarks
Having had for many years an interest in carbon nets, the present author witnessed
many astonishing developments connected to the chemical element carbon. The aro-
maticity associated with sp
2
-hybridized carbon atoms in certain cyclic structures is
responsible for the amazing formation of fullerenes and nanotubes, as well as for
the isolation of sturdy one-atom thick graphene sheets. The minimized electronic
repulsion associated with staggered conformation of sp
3
-hybridized C-C bonds
is responsible for diamond being one of the hardest materials, for the presence
of diamondoid hydrocarbons (diamondoids) in petroleum, and for the promis-
ing semiconductors obtained by epitaxial deposition yielding diamond-like films.
The discovery of methods to isolate and purify naturally occurring diamondoids
opened new perspectives for using such hydrocarbons in various applications after
functionalization.
However, most praise should be addressed not to the element carbon, but to its
compounds. Already from the infinity of chemical compounds, more than 7
10
7
organic substances have been characterized and registered, and they are by far more
numerous than compounds of all other elements heavier than hydrogen. It is not due
to chance that life is based on carbon compounds. What is amazing is that the element
carbon with an abundance of only 0.08 % in the accessible earth's crust, oceans, and
atmosphere (14th place among all elements) in its most oxidized form of carbon
dioxide can be converted (at all latitudes on land or in oceans by bacteria, algae, and
plants using water vapor and sun's energy) into carbohydrates and oxygen, thanks
to the elaborate machinery of photo-assimilation. In the not too distant future, when
mankind will have exhausted all fossil fuels (oil, coal, and natural gas) returning the
element carbon to the climate-foe CO
2
due to greenhouse-effects, much more energy
will be needed to make foods, plastics, and textiles by gaining access to carbon from
calcium carbonate rocks. Will we be ready?
×
References
Balaban AT (1969) Tetrahedron 25:2949-2956
Balaban AT (1980) Pure Appl Chem 52:1409-1429
Balaban AT (1989) Computers Math Applic 17:397-416 (Reprinted In: Hargittai I (ed) Symmetry
II, Pergamon Press, Oxford, pp. 397-416)
Balaban AT (1998) In: Parkanyi C (ed) Theoretical organic chemistry. Elsevier, Amsterdam, pp.
381-404
