Chemistry Reference
In-Depth Information
In topics edited by Diudea (Diudea
2005
; Diudea and Nagy
2013
) one may read
about some other possible types of diamond nets. It is stimulating to look at an
ornamental diamond jewel with dimensions
d
measured in millimeters, and to think
that one can look at this single
macromolecule
in which the carbon atoms constitute
most of the atoms (their number is proportional to
d
3
), whereas any peripheral atoms
such as H are much less numerous (their number is proportional to
d
2
).
The history of diamond hydrocarbons (or diamondoids for short) starts in 1933
with Landa's discovery of adamantane in petroleum (Landa and Mahacek
1933
),
confirmed a few years later by its elaborate synthesis (Prelog and Seiwerth
1941
). The
story might have ended there but for two fortuitous events. The first was Schleyer's
serendipitous finding that AlCl
3
catalyzes the isomerization of the hydrogenated
cyclopentadiene dimer into adamantane (Schleyer
1957
,
1990
). This discovery was
made possible by adamantane's incredible volatility, paradoxically associated with
a high melting point (actually adamantane sublimes around 270
◦
without melting)
(Mansoori et al.
2012
). Soon afterwards Schleyer and his coworkers succeeded
in synthesizing diamantane and triamantane using similar isomerizations (Cupas
et al.
1965
; Williams et al.
1966
; Fort and Schleyer
1964
; Fort
1976
). The driving
force in these reactions is increased thermodynamic stability: diamondoids are the
perfect hydrocarbons for sp
3
hybridization. Unfortunately, the labyrinth of 1, 2-
rearrangements becomes too complicated and only one tetramantane isomer could
be obtained synthetically (Burns et al.
1976
; McKervey
1980
).
The IUPAC name of diamondoid hydrocarbons ([
n
]polymantanes) based on von
Baeyer's conventions for polycyclic hydrocarbons becomes extremely awkward as
the number
n
of adamantane units increases, as will be seen in the next paragraph. One
must also take into account that starting with
n
4 more than one isomer is possible,
so that one needs a shorter and simpler name, as well as a coding system and an
understanding on how the carbon atoms are partitioned among quaternary, tertiary,
and secondary groups. This was achieved by means of dualists (inner dual graphs)
whose vertices are the centers of adamantane units and whose edges connect adjacent
vertices corresponding to adamantane units sharing a cyclohexane ring. The code is
simply a sequence if digits 1, 2, 3, or 4 representing the four tetrahedral directions
around a carbon atoms according to simple conventions of minimizing the number
in that sequence (Balaban and Schleyer
1978
). Dualists are a special kind of graphs,
in which the angles between edges do matter. For specifying substituent positions,
however, IUPAC names have to be used; a general procedure to find IUPAC names
exists for zigzag catamantanes (Balaban and Rücker
2013
).
Adamantane is tricyclo[3
.
3
.
1
.
1
3,7
]decane; it has molecular formula C
10
H
16
and
partitioned formula (CH)
4
(CH
2
)
6
. Diamantane is pentacyclo[7.3.1.1
4,12
.0
2,7
.0
6,11
]
tetradecane and has code [1]; it has molecular formula C
14
H
22
and partitioned formula
(CH)
6
(CH
2
)
8
. Triamantane is heptacyclo[7.7.1.1
3,15
.0
1,12
.0
2,7
.0
4,13
.0
5,11
]octadecane
and has code [12]; it has molecular formula C
18
H
26
and partitioned formula
C(CH)
8
(CH
2
)
9
. These diamondoids are unique isomers (Fig.
1.4
), but starting with
n
=
=
4, more than one isomeric [
n
]polymantane are possible.
By means of dualists it was possible to classify polymantanes into
catamantanes
when their dualists are acyclic, perimantanes when they have dualists containing
