# Bond angles and intermolecular forces present?

May 30, 2016

Here's what I got.

#### Explanation:

You can give the approximate value of those angles by looking at the hybridization of the two adjacent carbon atoms.

For angle $\alpha$, the carbon atom, which belongs to a carboxyl group, $- \text{C"("O")"OH}$, is surrounded by three regions of electron density

• a single bond to the oxygen atom that belongs to the hydroxyl group, $- \text{OH}$
• a double bond to the other oxygen atom
• a single bond to another carbon atom

This means that the carbon atom has a steric number equal to $3$, and thus uses $3$ hybrid orbitals to form the aforementioned bonds.

As a result, this carbon atom will be ${\text{sp}}^{2}$ hybridized, which implies that the $\alpha$ angle is approximately ${120}^{\circ}$.

For angle $\beta$, the carbon atom, which belongs to a methyl group, $- {\text{CH}}_{3}$, is surrounded by four regions of electron density

• a single bond to another carbon atom
• three single bonds to hydrogen atoms

This carbon has a steric number equal to $4$, and thus uses $5$ hybrid orbitals to form the aforementioned bonds.

As a result, this carbon atom will be ${\text{sp}}^{3}$ hybridized, which implies that the $\beta$ angle is approximately ${109.5}^{\circ}$.

This can be seen by looking at a molecule of pyruvic acid

Now, a pyruvic acid molecule is polar because of the presence of the carboxyl group and of the carbonyl group, $- \text{C=O}$.

This means that it exhibits dipole - dipole interactions due to the existence of permanent dipoles.

Moreover, because pyruvic acid has a hydrogen atom directly bonded to an oxygen atom in the hydroxyl group, it can act as a hydrogen bond donor.

The molecule can also act as a hydrogen bond acceptor due to the presence of the carbonyl group, which means that pyruvic acid can form hydrogen bonds.

Finally, all molecules, regardless if they are polar or non-polar, exhibit London dispersion forces due to random variations in the distribution of their electron clouds.