Question

For Polarimetry and Infrared Spectrometry in chemistry lab, please answer the following:

a. If a bond stretches in the forest, and the dipole moment doesn't change, does it make an absorption?

b. A sample gives strong peaks at both 3300 and 1750. What kind of compound might it be? Would it make a difference whether the peak at 3300 is described as very broad or just broad?

c. Someone said that IRs of aromatic compounds are "more spiky" than those of the corresponding aliphatics. Recast this description in less colorful, more boring, but perhaps more accurately detailed terms

Answer 1

Ans . a. No, if there is only bond stretching and no change in dipole moment ,it does not make it an absorption.For eg in the case of acetylene there is C-C bond stretching ,but no change in dipole moment and the compound is optically inactive.Thus we get a zero wavenumber of the absorbance .

b. As the compound gives a strong peak at 3300 cm^-1 , it surely contains C-H sp hybridized and for the peak at 1750 cm^-1 , chances are it would be an ester with the carbonyl carbon conjugated with the alkyne .

Yes it would make a difference as , if the the peak is described as very broad at 3300 cm^-1 then it surely contains an O-H bond that is undergoing hydrogen bonding.