Question

An infrared spectrum shows energy absorbed by a molecule that corresponds to the energy needed for a bond in that molecule to vibrate. Explain why the carbonyl stretching vibration (C=O) varied for the molecules (benzophenone, salicylic acid, ethyl butyrate, hexanal) used in this part of the experiment. Why do certain compounds show a higher vibrational frequency for C=O, while others show a lower vibrational frequency? Clearly explain your reasoning.

Answer 1

The vibrational frequency of the carbonyl stretching vibration (C=O) in molecules varies depending on factors such as the polarity of the bond and the strength of IR absorption.

Step-by-step explanation:

The energy absorbed by a molecule in an infrared spectrum corresponds to the energy needed for a bond in the molecule to vibrate. The carbonyl stretching vibration (C=O) varies for different molecules due to factors such as the polarity of the bond and the strength of IR absorption.

The carbonyl bond is very polar and absorbs IR light strongly, leading to a higher vibrational frequency. On the other hand, the carbon-carbon triple bond in alkynes is less polar and absorbs IR light weakly, resulting in a lower vibrational frequency.

Overall, the vibrational frequency of a bond in a molecule depends on the dipole moment of the bond and the energy associated with the wavelength of absorbed radiation.