Diamondoids from nature

There exist a number of other methods for the separation of diamondoids from petroleum fluids or natural gas streams (1) a gradient thermal diffusion process [54] is proposed for separation of diamondoids (2) a number of extraction and absorption methods [53,83] have been recommended for removing diamondoid compounds from natural gas streams and (3) separation of certain diamondoids from petroleum fluids has been achieved using zeolites [56, 84] and a number of other solid adsorbents. 

Adamantane and other diamondoids are constituents of petroleum, gas condensate (also called NGL or natural gas liquid), and natural gas reservoirs [52-56]. Adamantane was originally discovered [40] and isolated from petroleum fractions of the Hodonin oil fields in Czechoslovakia in 1933. 

In the analysis of the topology of such nets we can look for a classification scheme that will allow one to uniquely assign equal nets (up to isomorphism) derived from totally different crystal structures. Remember that the topology is not influenced by the metrical properties of the structure (angles, distances), so that a 4-connected diamondoid net is such, even if highly distorted (the geometry around the nodes could be far from tetrahedral), and also, obviously, is not dependent on the chemical nature of each node/vertex. 

As Nature offers diamondoids in large quantities from crude oil [4, 127], one ought to explore their chemistry especially in view of their potential applications in nanoelectronic devices [128]. The first challenge is to understand systematically the reactivity patterns of diamondoids, especially with respect to their selective peripheral C-H bond functionalization. This difficulty is emphasized when one considers that even triamantane (3) reacts with typical electrophiles (e.g., Br2) with very low selectivity [129]. What alternatives are there - will ionic, radical, and radical ionic C-H activation reactions eventually lead to higher C-H bond selectiv-ities These questions can, in part, be answered by computational methods when considering the very different stabilities of the cations, radicals, and radical cations of the respective diamondoids in the first step. These purely thermodynamic stabilities very often translate nicely into selectivities, at least for cationic structures. As this is often not the case for radicals, transition structures also have to be considered which makes the prediction of selectivities far more elaborate [130]. 

Adamantane and other light diamondoids are constituents of petroleum and they deposit in natural gas and petroleum crude oil pipelines causing fouling [13,16,17]. Adamantane was originally discovered and isolated from Czechoslovakian petroleum in 1933. The isolated substance was named adamantane, from the Greek for diamond. This name was chosen because it has the same structure as the diamond lattice, highly symmetrical and strain free. Acmally their carbon atom structure can be superimposed upon a diamond lattice. It is generally accompanied by small amounts of alkylated adamantane 2-methyl- 1-ethyl- and probably 1-methyl- 1,3-dimethyl and others. 

The semiclassical approach heavily relies on the empirical interactions. As in many molecular systems, diamondoids have both intramolecular and intermolecular interactions. Intramolecular interactions reflect the bonding nature of the system. For instance, C-H bonds have very different potential surfaces from those of C-C bonds, to which they are also related whether the bonds are single, double, or triple. The Lennard-Jones potential is probably the simplest one to use. In general, a two-body potential can be expanded as... 

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