There are three carbon–oxygen bonds in methyl acetate.

a.What are their relative bond lengths?

b.What are the relative infrared (IR) stretching frequencies of these bonds?

In a molecule, when an electric charge is spread over more than one atom, delocalization happens.In chemistry, delocalized electrons are electrons in a molecule or ion that are not associated with a single covalent bond.

The value of stretching vibration frequency of bond can be calculated using Hooke’s Law.

According to Hooke’s law, vibrational frequency of a bond is directly proportional to bond strength and inversely proportional to masses at the end of the bond. Hooke’s law is mathematically represented as $\overline{v}=\frac{1}{2\pi c}\sqrt{\frac{K}{\mu }}$,where K is force constant or bond strength and $\mu$is reduced mass$\mu =\frac{m_1{m}_2}{m_1+m_2}$

The bond between oxygen and methyl group is longest (3), because it is a pure single bond, whereas other two carbon-oxygen bonds have some double bond character due to localization.

The shortest bond is between carbon and the carbonyl oxygen (1), because it has the most double bond character as compared to the other (C-O) (2).

We know from step 2 that the longer the bond, the lower its IR stretching frequency.

1 = Highest frequency, because it has shortest bond length.

2 = Medium frequency, due to delocalization which decreases its bond length.

3 = Lowest frequency, because the bond between oxygen and methyl group is longest.