which compounds below that have a vibration that is infrared inactive. and indicate the specfic vibration that is infrared inactive.
1) acetone
2) 1-butyne
3) 2-butyne
4) water
5) chlorine
To determine which compounds have infrared (IR) inactive vibrations, we need to consider the symmetry of the molecules. IR spectroscopy measures the absorption of infrared radiation by chemical bonds, which causes their vibrations.
1) Acetone (CH₃COCH₃):
This compound has a carbonyl group (C=O) stretching vibration that is IR active. However, the methyl (CH₃) symmetric and asymmetric stretching vibrations should be IR inactive, meaning they do not absorb infrared radiation.
2) 1-Butyne (CH₃C≡CCH₃):
1-Butyne lacks any vibrational motions that are IR inactive. The C≡C triple bond stretching vibration is IR active and will absorb infrared radiation.
3) 2-Butyne (CH₃CH≡CCH₃):
Similar to 1-butyne, 2-butyne has an IR active C≡C triple bond stretching vibration. There are no vibrations in this compound that are infrared inactive.
4) Water (H₂O):
Water has a variety of vibrational modes, including stretching and bending motions. The O-H stretching vibrations are IR active and strongly absorb infrared radiation. Therefore, water does not have any vibrations that are infrared inactive.
5) Chlorine (Cl₂):
Chlorine (Cl₂) is a diatomic molecule, and its movement and vibrations are limited. It only has the stretching and bending vibrations, which are all IR active. Therefore, it does not have any vibrations that are infrared inactive.
In summary, 1-butyne, 2-butyne, water, and chlorine do not have any vibrations that are infrared inactive. Acetone has the methyl stretching vibrations (symmetric and asymmetric) that are infrared inactive, while its carbonyl stretching vibration is infrared active.