In chemistry, diamondoids are variants 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. These species are of interest as molecular approximations of the diamond cubic framework, terminated with C−H bonds. Cyclohexamantane may be thought of as a nanometer-sized diamond of approximately 5.6×10−22 grams.
- Adamantane (C10H16)
- Iceane (C12H18)
- BC-8 (C14H20)
- 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
- Cyclohexamantane (C26H30)
- Super-adamantane (C30H36)
One tetramantane isomer is the largest ever diamondoid prepared by organic synthesis using a keto-carbenoid reaction to attach cyclopentane rings. Longer diamondoids have been formed from diamantane dicarboxylic acid. The first-ever isolation of a wide range of diamondoids from petroleum took place in the following steps: 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. This allows their anchorage to a gold surface and formation of self-assembled monolayers (diamond-on-gold). Additionally, functionalized diamondoids (adamantanes) have been proposed as molecular building blocks for self-assembled molecular crystals.
Organic chemistry of diamondoids even extends to pentamantane. 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 pentamane 1 with bromine exclusively gives the medial bromo derivative 2 which on hydrolysis in water and DMF forms the alcohol3.
In contrast nitroxylation of 1 with nitric acid gives the apical nitrate4 as an intermediate which is hydrolysed to the apical alcohol5 due to the higher steric demand of the active electrophilicNO−
3 species. This alcohol can react with thionyl bromide to the bromide 6 and in a series of steps (not shown) to the corresponding thiol. Pentamantane can also react with tetrabromomethane and tetra-n-butylammonium bromide (TBABr) in a free radical reaction to the bromide but without selectivity.