Question 8.6: Phosgene is a colorless, highly toxic gas. When dilute with ......
Phosgene is a colorless, highly toxic gas. When dilute with air, it has an odor resembling newly mown hay. Thionyl chloride is used as a chlorinating agent in organic synthesis and as a solvent in some lithium batteries. Compare the shapes of the phosgene, COCl_{2}, and the thionyl chloride molecules, SOCl_{2}.
The Lewis formulas for these two molecules are
\begin{matrix} ^{.^{.}}O^{^{.}.} \\ _{_{\diagup }} \overset{||}{C}_{_{\diagdown }} \\ _{^{.}.}^{.^{.}}Cl_{.^{.}} \quad _{^{.}.}Cl_{.^{.}}^{^{.}.} \\ phosgene \end{matrix} and \begin{matrix}:\overset{..}{\underset{..}{Cl}}-\overset{\ \ ..^{\oplus }}{S}-\overset{..}{\underset{..}{Cl}}: \\ :\overset{|}{\underset{\ \ .._{\circleddash }}{O}}: \\ thionyl\ chloride \end{matrix}
A phosgene molecule belongs to the class AX_{3} and therefore is trigonal planar, like a formaldehyde molecule. The lone pair on the sulfur atom in a thionyl chloride molecule puts this molecule in the AX_{3}E class. Thus, a thionyl chloride molecule is trigonal pyramidal, with the two chlorine atoms and the oxygen atom lying in a plane and the sulfur atom lying above the plane.
Notice that even though the chemical formulas for a phosgene molecule and a thionyl chloride molecule are similar, the shapes of the two molecules are different because of the lone electron pair on the central sulfur atom in the thionyl chloride molecule.