# Distinguish between the pair of compounds by their infrared spectra: Compound A CH3CH2CH2N(CH3)2...

## Question:

Distinguish between the pair of compounds by their infrared spectra:

Compound A CH3CH2CH2N(CH3)2 and Compound B CH3CH2CH2NH2

a. Compound A will show an NH absorption while Compound B will not.

b. Compound B will show an NH absorption while Compound A will not.

c. The infrared spectra will be the same for both compounds.

d. There is no way to differentiate between the two compounds using IR.

## Infrared Spectroscopy

Infrared spectroscopy is a powerful tool used in organic chemistry to determine what functional groups are present in a compound. Bonds are constantly vibrating; stretching and bending. The frequency at which these vibrations occur are different for different bonds. The two factors that change the frequency at which a bond vibrates are the stiffness of the bond i.e. bond order, and the mass of the atoms within a bond.

The equation which relates the frequency of light that a molecule will absorb in order to vibrate, and also shows how the stiffness of a bond and mass can affect this frequency, is:

{eq}\nu\ =\ \frac{1}{2\pi}\ \sqrt\frac{k}{\mu} {/eq}

k is the force constant of a bond, measured in N/cm, which corresponds to the stiffness of a bond. {eq}\mu {/eq} is the reduced mass of the bond measured in kg, and {eq}\nu {/eq} is the frequency of vibration given in cm{eq}^-1 {/eq}

Compound A and B differ in that the nitrogen (N) atoms are bonded to different species. In compound A, the nitrogen is bonded to two CH{eq}_3 {/eq}...

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