The frequency shift of the carbonyl absorption in the cyclohexane carboxaldehyde is -

Concept:

• Carbonyl IR Absorption: The carbonyl group (C=O) has a characteristic absorption frequency in the infrared (IR) spectrum.

  • For aldehydes, the typical carbonyl stretch appears around 1720-1740 cm^-1.

  • For ketones, the carbonyl stretch is typically around 1705-1750 cm^-1.

• Factors Affecting Carbonyl IR Frequency:

  • Conjugation: Conjugation with a double bond or aromatic ring can lower the carbonyl stretching frequency by providing delocalization of electrons, typically shifting it to a lower wavenumber.

  • Substitution Effect: Electronegative substituents (like halogens) can increase the carbonyl stretching frequency by withdrawing electron density, leading to a higher wavenumber.

  • Ring Strain: Ring strain in cyclic structures can also influence the carbonyl stretch; smaller ring sizes generally shift the frequency to higher wavenumbers due to increased ring strain.

Explanation:​

1730 cm^-1:

• This frequency is within the typical range for aldehyde carbonyl absorption, including cyclohexane carboxaldehyde, which typically exhibits a carbonyl stretch around 1720-1740 cm^-1.

Conclusion:

The correct frequency shift of the carbonyl absorption in cyclohexane carboxaldehyde is: 1730 cm^-1