Question

Which of the following regarding the characteristics of IR is false?

A. Compounds that are capable of hydrogen bonding will typically have a broad O-H or N-H peak present in the IR spectrum
B. The fingerprint region is between 500-1500 cm⁻¹
C. The intensity of an IR peak is dependent on the dipole moment of the bond its representing
D. Compounds with similar functional groups have perfectly identical IR spectra
E. Conjugation (alternating pi bonds) can decrease the wavenumber at which a C=O bond is observed

Answer 1

The false statement is that the intensity of an IR peak is solely dependent on the dipole moment of the bond it represents. In truth, intensity is linked to the polarity change during vibration, and conjugation does decrease the wavenumber for a carbonyl bond's absorption in IR spectroscopy.

Step-by-step explanation:

The false statement regarding the characteristics of Infrared (IR) spectroscopy is that the intensity of an IR peak is dependent on the dipole moment of the bond it's representing. In reality, the intensity of an IR absorption peak is closely related to the change in dipole moment that occurs during the vibrational motion of the bond. Vibrations that lead to a larger change in the dipole moment tend to have stronger absorption peaks.

Moreover, conjugation, which involves alternating pi bonds, has a noticeable effect on absorption. Specifically, conjugation can decrease the wavenumber at which a carbonyl (C=O) bond absorbs. This happens because the conjugation allows for a greater delocalization of electrons, effectively lowering the energy required for the vibration and thus reducing the wavenumber.

In summary, the statement that the intensity of an IR peak solely depends on the dipole moment is false, as it is also influenced by other factors like the polarity change during vibration. Additionally, conjugation indeed causes a shift to lower wavenumbers for the C=O absorption.