Iycee Charles de Gaulle Summary “C60 behaves chemically like an electron deficient

“C60 behaves chemically like an electron deficient

 “C60 behaves chemically like an electron
deficient alkene, since it has sp2
carbon atoms but tends to avoid double bonds in the pentagonal rings, which
causes poor electron delocalisation throughout the molecule” (Unwin, 2018) 3. This
means that C60 behaves chemically like an electron deficient alkene
and so readily takes place in addition reactions; like the addition of the
O-Os-O unit across 2 fused six-membered rings 1. Addition
reactions to metal atoms have recently been of particular interest. The
fullerene C60 offers a range of bonding modes to metal atoms: to the
exterior of the carbon cage; to the interior of the cage; connecting separate
parts of the cage together; etc. However, there’s no evidence to show whether a
metal atom could become part of the cage structure itself.

Buckminsterfullerene has an icosahedral symmetry closed cage
structure and is made up of 60 trivalent sp2
carbon atoms that form finite cages with 20 hexagons and 12 non-adjacent
pentagons. This structure of C60 cannot be directly confirmed by
X-ray crystallography because although the molecules stack readily enough, they
rotate at room temperature due to their nearly spherical symmetry. The
resultant disorder means that the atomic positions can’t be shown in a X-ray
crystallography spectrum 1. Instead, the structure was confirmed by
observing the structure of the first fullerene derivative synthesised – C60(OsO4)
1. This derivative has also been used to determine the ratio of 13C:12C
within C60(OsO4) when the C60 has been
partially enriched with 13C. Taking a13C NMR spectrum of C60
by itself would only give a single peak and show no coupling 1.   

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This changed in 1990, when Krätschmer, Huffman, et al.
managed to produce C60 in macroscopic quantities by producing an arc
across two graphite electrodes at about 3500oC under a low pressure
of He gas. In the mass spectra taken of the soot, aside from C60 and
its fragment ions, the existence of C70, the second most abundant
all-carbon molecule after C60, was also discovered. Aside from the Krätschmer-Huffman
method for synthesising fullerenes there are other methods such as burning the graphite
in a furnace, using negative ion/desorption chemical ionisation techniques,
using a benzene flame, etc. 2 However, the Krätschmer-Huffman
method is still the most commonly used. Pure C60 was isolated from
the soot later in 1990 by column chromatography. The process has been refined
to provide a higher yield of C60 by using two separate steps
Firstly, all Fullerenes are extracted from the soot using a Soxhlet extractor
with a solvent like Toluene; after that C60 was isolated from the
other fullerenes like C70 via column chromatography 2.

A new allotrope of carbon called Buckminsterfullerene C60
was first discovered in 1985 by Kroto, Smalley, et al. who recognised its existence
when they observed an unusually intense 720 m/e peak in the mass spectra of
soot produced when graphite was vaporised into a soot by a laser in a He
atmosphere. Due to this discovery, Curl, Kroto and Smalley were awarded the
1996 Nobel Prize in Chemistry. The scientific community was eager to investigate
the structure and properties of the molecule further; however, they were unable
to as C60 had only been found in microscopic quantities.