If the ends of the bonds are connected, the structure is that of a tetrahedron, a three-sided pyramid of four faces (including the base).
Every carbon atom is covalently bonded at the four corners of the tetrahedron to four other carbon atoms.
Of the stable nuclides, the isotope carbon-13 is of particular interest in that its nuclear spin imparts response in a device called a nuclear magnetic resonance spectrometer, which is useful when investigating the molecular structures of covalently bonded compounds containing carbon.The crystal structure of graphite is of a kind that permits the formation of many compounds, called lamellar or intercalation compounds, by penetration of molecules or ions.Graphitic oxide and graphitic fluoride are nonconducting lamellar substances not obtained in true molecular forms that can be reproduced, but their formulas do approximate, respectively, the compositions of carbon dioxide and carbon monofluoride.carbon-13 (1.07 percent); 14 radioactive isotopes are known, of which the longest-lived is carbon-14, which has a half-life of 5,730 ± 40 years.The rate of conversion of diamond to graphite is so slow, however, that a diamond persists in its crystal form indefinitely.As temperature rises, the rate of conversion to graphite increases substantially, and at high temperatures it becomes (thermodynamically) favourable if the pressure is sufficiently high.(They received the 2010 Nobel Prize in Physics for their work.) The greater degree of compactness in the diamond structure as compared with graphite suggests that by the application of sufficient pressure on graphite it should be converted to diamond.