Question

Which absorbs at higher frequencies: a C-H or C-D bond? Explain.

a) C-H bond
b) C-D bond
c) Both absorb equally
d) Neither absorbs

Answer 1

The C-D bond absorbs at higher frequencies compared to the C-H bond due to its greater polarity.

Step-by-step explanation:

The C-D bond absorbs at higher frequencies compared to the C-H bond.

Bonds absorb infrared light based on the change in dipole moment of the molecule. The greater the polarity of the bond, the stronger its infrared (IR) absorption. Since the C-D bond is less polar than the C-H bond, it absorbs at higher frequencies. This is because the C-D bond has a larger difference in electronegativity compared to the C-H bond, resulting in a stronger IR absorption.

For example, let's consider the stretching vibration of the C-D and C-H bonds. The C-D bond has a higher frequency and absorbs at around 2200 cm⁻¹, while the C-H bond has a lower frequency and absorbs at around 3000 cm⁻¹.