Question

Which of the following vibrational mode shows no IR absorption bands:

• A. symmetric $CO_2$ stretch
• B. antisymmetric $CO_2$ stretch
• C. CH3C≡ CHstretch
• D. symmetric O=C=S stretch

Hint:

Vibrational modes that involve a change in dipole moment are IR active, while those that do not, like symmetric CO2 stretch, are IR inactive.

Answer 1

The Correct Option is A

The symmetric stretching of \(CO_2\) does not alter the dipole moment; therefore, it does not absorb infrared (IR) radiation. Conversely, other vibrational modes, such as the antisymmetric stretch and the CC stretch, induce a change in the dipole moment and exhibit IR absorption.