In chemistry, diamondoids are generalizations of the
carbon cage molecule known as
adamantane (C10H16), the smallest unit cage structure of the
diamondcrystal lattice. Diamondoids also known as nanodiamonds or condensed adamantanes may include one or more cages (adamantane,
diamantane,
triamantane, and higher polymantanes) as well as numerous isomeric and structural variants of adamantanes and polymantanes. These diamondoids occur naturally in
petroleum deposits and have been extracted and purified into large pure crystals of polymantane molecules having more than a dozen adamantane cages per molecule.[1] These species are of interest as molecular approximations of the
diamond cubic framework, terminated with C−H bonds.
Diamantane (C14H20) also diadamantane, two face-fused cages
Triamantane (C18H24), also triadamantane. Diamantane has four identical faces available for anchoring a new C4H4 unit.
Isotetramantane (C22H28). Triamantane has eight faces on to which a new C4H4 unit can be added resulting in four
isomers. One of these isomers displays a helical twist and is therefore
prochiral. The
P and Menantiomers have been separated.
Pentamantane has nine isomers with chemical formula C26H32 and one more pentamantane exists with chemical formula C25H30
One tetramantane isomer is the largest ever diamondoid prepared by
organic synthesis using a keto-
carbenoid reaction to attach cyclopentane rings.[3] Longer diamondoids have been formed from diamantane dicarboxylic acid.[4] The first-ever isolation of a wide range of diamondoids from petroleum took place in the following steps:[1] a
vacuum distillation above 345 °C, the equivalent
atmospheric boiling point, then
pyrolysis at 400 to 450 °C in order to remove all non-diamondoid compounds (diamondoids are thermodynamically very stable and will survive this pyrolysis) and then a series of
high-performance liquid chromatography separation techniques.
In one study a tetramantane compound is fitted with
thiol groups at the bridgehead positions.[5] This allows their anchorage to a
gold surface and formation of
self-assembled monolayers (diamond-on-gold).
Organic chemistry of diamondoids even extends to pentamantane.[6] The medial position (base) in this molecule (the isomer [1(2,3)4]pentamantane) is calculated to yield a more favorable
carbocation than the apical position (top) and simple
bromination of pentamantane 1 with
bromine exclusively gives the medial bromo derivative 2 which on hydrolysis in water and
DMF forms the
alcohol3.
Diamondoids are found in mature high-temperature
petroleum fluids (volatile oils, condensates and wet gases). These fluids can have up to a spoonful of diamondoids per US gallon (3.78 liters). A review by Mello and Moldowan in 2005 showed that although the carbon in diamonds is not biological in origin, the diamondoids found in
petroleum are composed of carbon from biological sources. This was determined by comparing the ratios of carbon
isotopes present.[7]
Optical and electronic properties
The
optical absorption for all diamondoids lies deep in the
ultraviolet spectral region with optical
band gaps around 6
electronvolts and higher.[8] The spectrum of each diamondoid is found to reflect its individual size, shape and
symmetry. Due to their well-defined size and structure diamondoids also serve as a model system for electronic structure calculations.[9]
Many of the optoelectronic properties of diamondoids are determined by the difference in the nature of the
highest occupied and lowest unoccupied molecular orbitals: the former is a
bulk state, whereas the latter is a
surface state. As a result, the energy of the lowest unoccupied molecular orbital is roughly independent of the size of the diamondoid.[10][11]
^Dahl, J. E. P.; Moldowan, J. M.; Peakman, T. M.; Clardy, J. C.; Lobkovsky, E.; Olmstead, M. M.; May, P. W.; Davis, T. J.; Steeds, J. W.; Peters, K. E.; Pepper, A.; Ekuan, A.; Carlson, R. M. K. (2003). "Isolation and Structural Proof of the Large Diamond Molecule, Cyclohexamantane (C26H30)". Angewandte Chemie International Edition. 42 (18): 2040–2044.
doi:
10.1002/anie.200250794.
PMID12746817.
^Burns, W.; McKervey, M. A.; Mitchell, T. R.; Rooney, J. J. (1978). "A New Approach to the Construction of Diamondoid Hydrocarbons. Synthesis of anti-Tetramantane". Journal of the American Chemical Society. 100 (3): 906–911.
doi:
10.1021/ja00471a041.
^Zhang, J.; Zhu, Z.; Feng, Y.; Ishiwata, H.; Miyata, Y.; Kitaura, R.; Dahl, J. E.; Carlson, R. M.; Fokina, N. A.; Schreiner, P. R.; Tománek, D.; Shinohara, H. (Mar 25, 2013). "Evidence of diamond nanowires formed inside carbon nanotubes from diamantane dicarboxylic acid". Angewandte Chemie International Edition. 52 (13): 3717–3721.
doi:
10.1002/anie.201209192.
PMID23418054.
^Tkachenko, Boryslav A.; Fokina, Natalie A.; Chernish, Lesya V.; Dahl, Jeremy E. P.; Liu, Shenggao; Carlson, Robert M. K.; Fokin, Andrey A.; Schreiner, Peter R. (2006). "Functionalized Nanodiamonds Part 3: Thiolation of Tertiary/Bridgehead Alcohols". Organic Letters. 8 (9): 1767–70.
doi:
10.1021/ol053136g.
PMID16623546.
^Fokin, Andrey A.; Schreiner, Peter R.; Fokina, Natalie A.; Tkachenko, Boryslav A.; Hausmann, Heike; Serafin, Michael; Dahl, Jeremy E. P.; Liu, Shenggao; Carlson, Robert M. K. (2006). "Reactivity of [1(2,3)4]Pentamantane (Td-Pentamantane): A Nanoscale Model of Diamond". The Journal of Organic Chemistry. 71 (22): 8532–8540.
doi:
10.1021/jo061561x.
PMID17064030.