Question

Explain the following:

True/False: Two different compounds with the same functional groups will have the same IR spectra?

True/False: IR absorption frequency between functional groups varies greatly?

The mass of the atoms in a bond is directly or inversely proportional to the vibrational frequency?

Will the conjugation of pi bonds increase or decrease the frequency of the peak?

Answer 1

(1) This statement is false. Two different compound with same functional group will also have different IR spectra for example:- In the methanol and phenol both have same functional group but Will have different IR spectra because of the difference in absorption frequency of the other bonds.

(2) This statement is True. IR absorption frequency of functional group varies greatly.For example the value of stretching frequency for OH group is almost 3500-3600 and for NH in NH2 group is between 3200-3300 .

(3) The mass of an atom in bond inversely related to the vibrational frequency because we know the equation. Vibrational frequency= 1/2π√K/u here u= reduced mass hence it is inversely related to the vibrational frequency.

(4) The conjugation of pie bond will decrease the IR frequency of the peak. For example The ketone group have IR frequency between 1600-1700 but after increase in the conjugation of pie bond that related to this group will decrease the absorption frequency.

I hope you understand