Question 8.2: predicting Shape in Molecules with More than One central ato...
Predicting Shape in Molecules with More Than One Central Atom
Pyruvic acid is a key substance in the metabolism of both carbohydrates and several amino acids. Describe the geometry around each of the central atoms in pyruvic acid, and draw the overall shape of the molecule.
\begin{matrix} & \underset{|}{ H} && \underset{||}{O} && \underset{||}{O} & & \\ H-& C&-&C&-&C&-& O&-&H \\ & \overset{|}{H} &&&&& \end{matrix} \\ \quad \quad \quad \text{Pyruvic acid}
STRATEGY
Use the VSEPR model to predict the geometric arrangement of charge clouds around each of the three carbon atoms. Draw the overall molecule showing the bond angles predicted by VSEPR and using dashed lines and wedges to represent three-dimensional shape.
The carbon on the left has four charge clouds (four single bonds) and tetrahedral geometry with 109.5° bond angles. Both the carbon in the middle and on the right have three charge clouds (two single bonds and one double bond) and trigonal planar geometry with 120° bond angles.
