The oxides and sulphides of carbon

In this molecule, which has a very small (possibly zero) dipole moment, the bond length is M31 A. The length, force constant, and bond energy (Table 21.4) show that it is best represented C=0. 

Bond Length Force constant Bond energy 

The molecules OCO, SCS, and OCS are linear. Bond lengths are given in Tables 21.5 and 21.6. In carbon dioxide the carbon-oxygen bond is intermediate in length between a double and triple bond. The studies of CO2 and CS2 by high resolution infrared spectroscopy provide an example of the use of this method for molecules which cannot be studied by the microwave method because they have no permanent dipole moment. The structure of the CS2 molecule has also been studied in the crystalline state. (C—S, 1-56 A). Under a pressure of 30 kbar CS2 polymerizes to a black solid for which a chain structure has been suggested.  

The third oxide of carbon, the so-called suboxide C3O2, is a gas at ordinary temperatures (it bods at +6°C) and may be prepared by heating malonic acid or its diethyl ester with a large excess of phosphorus pentoxide at 300°C. Its preparation from, and conversion into, compounds containing the —C—C-C- nucleus are consistent with its structure, 0-C—C—C—O. The action of water regenerates malonic acid, ammonia yields malonamide, and HCl malonyl chloride  

Carbon suboxide polymerizes readily at temperatures above —78°C. An e.d. study indicates a linear molecule with C-C, 1-28 A, and C-0, 1-16 but the possibility of small deviations from linearity could not be excluded. 

---