Diamondoid

, diamantane, triamantane and one isomer of tetramantane Examples include: • 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 M enantiomers 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: 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. 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 alcohol 3. In contrast nitrooxylation of 1 with nitric acid gives the apical nitrate 4 as an intermediate which is hydrolysed to the apical alcohol 5 due to the higher steric demand of the active electrophilic 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. == Origin and occurrence ==

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. == 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. 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. 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. Diamondoids have been found to exhibit a negative electron affinity, making them potentially useful in electron-emission devices. ==See also==