Carbon: atomic number color, 6 compounds

The other members of the series are prepared in a similar manner. Increasing the number of carbon atoms in the cation increases the solubility of the corresponding compound in ethanol. If the solid product does not separate when the alkylammonium chloride is added to the blue solution of chromium(ll), the excess solvent should be removed from the flask by distillation. At the point where the crystals begin to appear, the oil bath is lowered and the solution (deep-blue color) is allowed to cool slowly. Beautiful shiny platelet crystals separate. An alternative procedure is to start with a smaller volume of solvent and saturated solutions of alkylammonium chlorides (e.g., in the case of (C2HsNH3)2[CrCl4], 40 mL of EtOH). 

Figure 1-3 Concentrations of alkanes (hydrocarbons with the formula CnH2n+2) found in rainwater in Hannover, Germany, in the winter and summer in 1989 are measured in parts per billion (= jutg hydrocarbon/L of rainwater). Summer concentrations are higher, and compounds with an odd number of carbon atoms (colored bars) predominate. Plants produce mainly hydrocarbons with an odd number of carbon atoms. [From K. Levsen,...

Molecular model 20A shows that the two hydrogen atoms on one terminal carbon (the CH2 unit) are perpendicular to the hydrogen atoms on the other terminal carbon (the other CH2 unit). The electron density map of allene (see 20C) shows the higher concentration of electron density (red color) is between the carbon atoms, but in different planes. This model confirms that the two 7t-bonds are perpendicular to one another. Substituted allenes are also named as dienes. For example, compound 21 has the C=C=C unit as part of a seven-carbon chain, so it is a heptadiene. Giving the cumulative diene unit the lower numbers leads to 2-methyl-2,3-heptadiene as the name for 21. 

Properties Dark-colored crystals (the octahedral form in which the atoms have the diamond arrangement). The amorphous form is a dark-brown powder (see silicon, amorphous). D 2.33, mp 1410C, bp 2355C, Mohs hardness 7, dielectric constant 12, coordination number 6. Soluble in a mixture of nitric and hydrofluoric acids and in alkalies insoluble in water, nitric acid, and hydrochloric acid. Combines with oxygen to form tetrahedral molecules in which one silicon atom is surrounded by four oxygen atoms. In this respect it is similar to carbon. It is also capable of forming -Si=Si- double bonds in orga-nosilicon compounds. 

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