Atomic properties, carbon compared with

Quantitative investigations of the effect of the carbon content on the structure and physical properties of boron-rich solids have been restricted to p-rhombohedral boron and boron carbide (56-61). Up to carbon contents of about 1 at.% in p-rhombohedral boron, the carbon atoms substitute statistically for boron atoms at the polar sites of the Bjj icosahedra in the structure with a maximum of one carbon atom per icosahedron. Compared with the boron atom, the... 

The NMR spectral properties of the parent heterocycles are summarized in Table 12. The signal for the pyrrole a-carbon is broadened as a result of coupling with the adjacent nitrogen-14 atom (c/. Section 3.01.4.3). While the frequencies observed for the /3-carbon atoms show a fairly systematic upheld shift with increasing electronegativity of the heteroatom, the shifts for the a-carbon atoms vary irregularly. The shifts are comparable with that for benzene, S 128.7. 

The color of diamond due to nitrogen impurities has been described in Section 9.6.3 It has been found that nitrogen impurities that are located next to a carbon vacancy in diamond thin films endow the solid with quite new properties, somewhat similar to the properties of a solid containing FLi centers compared with ordinary F centers. The diamond structure is built up of carbon atoms each surrounded by four... 

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