Carbon in Space

Carbon has of course a much longer history than can be traced back to our ancestors use of charcoal for ore reduction or soot for writing. 

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The remarkable stability of the cage structure makes fullerenes Important candidates for survival and wide distribution in space. Fullerenes of astronomical origin have been detected in meteorites and in and around an impact crater on the Long Duration Exposure Facility spacecraft (39). Laboratory simulations in combination with interstellar observations support the idea that the predominant fraction of carbon in space is present as solid macromolecular carbon (40) or amorphous and hydrogenated amorphous carbon (41). 

This paper should not end without giving some information on present and future applications of this anisotropic polymer carbon. In space technology, carbon fibre reinforced composites are the unique structural material. In aircraft industry all military planes make use of this revolutionary material. Fig. 26 shows the model of a future fighter which combines wings and stabilizers in one structural element. The whole structure consists of advanced composites. Only small parts, i.e. the engines are still made from metals. In today s commercial aircrafts only secondary and tertiary parts are made from CFRP, as shown in fig. 27. There is... 

Buckminsterfullerene is a superb modem example of the value of fundamental research to science in general and to applied areas in particular. Buckminsterfullerene was discovered by chemists doing experiments trying to determine the role of carbon in space and in the distant stars. The result was dynamic new paths in chemistry, physics, and materials science here on earth. 

Unlike the forces between ions which are electrostatic and without direction, covalent bonds are directed in space. For a simple molecule or covalently bonded ion made up of typical elements the shape is nearly always decided by the number of bonding electron pairs and the number of lone pairs (pairs of electrons not involved in bonding) around the central metal atom, which arrange themselves so as to be as far apart as possible because of electrostatic repulsion between the electron pairs. Table 2.8 shows the essential shape assumed by simple molecules or ions with one central atom X. Carbon is able to form a great many covalently bonded compounds in which there are chains of carbon atoms linked by single covalent bonds. In each case where the carbon atoms are joined to four other atoms the essential orientation around each carbon atom is tetrahedral. 

Electronic-Grade MMCs. Metal-matrix composites can be tailored to have optimal thermal and physical properties to meet requirements of electronic packaging systems, eg, cotes, substrates, carriers, and housings. A controUed thermal expansion space tmss, ie, one having a high precision dimensional tolerance in space environment, was developed from a carbon fiber (pitch-based)/Al composite. Continuous boron fiber-reinforced aluminum composites made by diffusion bonding have been used as heat sinks in chip carrier multilayer boards. 

Because a hexose contains four chiral carbon atoms, there are 2 = 16 different possible arrangements of the hydroxyl groups in space, ie, there are 16 different stereoisomers. The stmctures of half of these, the eight D isomers, are shown in Figure 1. Only three of these 16 stereoisomers are commonly found in nature D-glucose [50-99-7] D-galactose [59-23-4] and D-mannose [3458-28-4]. 

Stereochemistry refers to chemistry in three dimensions. Its foundations were laid by Jacobus van t Hoff" and Joseph Achille Le Bel in 1874. Van t Hoff and Le Bel independently proposed that the four bonds to carbon were duected toward the corners of a tetrahedron. One consequence of a tetrahedral ariangement of bonds to carbon is that two compounds may be different because the ariangement of their atoms in space is different. Isomers that have the same constitution but differ in the spatial ariangement of their- atoms are called stereoisomers. We have already had considerable experience with certain types of stereoisomers—those involving cis and bans substitution patterns in alkenes and in cycloalkanes. 

This illustrates an important distinction in chemical enumeration that between the enumeration of "structural" isomers, in which only the connections between the atoms are considered, and that of stereoisomers, in which the situation of a molecule in space is important, so that as above we can have right- and left-hand forms of a molecule. This distinction will occur, for example, when a carbon atom is bonded to four distinct substituents (it can occur in many other ways). Such a carbon atom is said to be asymmetrical. 

Structural isomers have identical molecular formulas, but their atoms are linked to different neighbors. Geometrical isomers have the same molecular and structural formulas but different arrangements in space. Molecules with four different groups attached to a single carbon atom are chiral they are optical isomers. 

A most important early addition to organic structure theory was made by the first Nobel Laureate in Chemistry, van t Hoff, who in 1874 recognized that the optical activity of carbon compounds can be explained by the postulate that the four valence bonds of the carbon atom are directed in space toward the comers of a tetrahedron. 

Composition. Air is a mixture of a large number of species with concentrations varying in space and time. Of particular interest are ozone and compounds of sulfur, nitrogen, and carbon, and their chemical interactions. 

The properties described above have important consequences for the way in which these skeletal tissues are subsequently preserved, and hence their usefulness or otherwise as recorders of dietary signals. Several points from the discussion above are relevant here. It is useful to ask what are the most important mechanisms or routes for change in buried bones and teeth One could divide these processes into those with simple addition of new non-apatitic material (various minerals such as pyrites, silicates and simple carbonates) in pores and spaces (Hassan and Ortner 1977), and those related to change within the apatite crystals, usually in the form of recrystallization and crystal growth. The first kind of process has severe implications for alteration of bone and dentine, partly because they are porous materials with high surface area initially and because the approximately 20-30% by volume occupied by collagen is subsequently lost by hydrolysis and/or consumption by bacteria and the void filled by new minerals. Enamel is much denser and contains no pores or Haversian canals and there is very, little organic material to lose and replace with extraneous material. Cracks are the only interstices available for deposition of material. 

The valence bonds of carbon have bxed directions and are equidistant in space, pointing from the center to the corners of a tetrahedron forming an angle of 109°. Thus, in propane, which we usually write as CH3-CH2 CH3, the carbon atoms are not connected in a straight line, but are actually as shown in the above three-dimensional diagram. 

Because of the atoms freedom to rotate about single bonds, a chain of carbon atoms can achieve various positions in space. On one extreme is the zig-zag extended chain and on the other is a coil. Such spatial structures become particularly important in determining properties of very long chained compounds known as polymers (Chapter 5). 

This drawing has a carbon in the center with four different groups ethyl, methyl, bromine, and chlorine. Therefore, we have a stereocenter. Anytime you have four different groups connected to a carbon atom, there will be two ways to arrange the groups in space (always two never more and never less). These two arrangements are different configurations ... 

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