Which of the following choices correctly ranks the molecules shown below in order of increasing stretching vibrational frequency?

Question

Quizplus · Accepted Answer

The stretching frequency of a bond is directly proportional to the bond strength and inversely proportional to the mass of the atoms involved in the bond. The molecule with the lowest stretching frequency is the one with the strongest bond and/or the heaviest atoms. Thus, molecule 3, with the triple bond between two carbon atoms, has the lowest stretching frequency. Molecule 1 has a double bond between two carbon atoms, which is less strong than a triple bond, so it has a higher stretching frequency than molecule 3. Molecule 2 has a double bond between a carbon atom and an oxygen atom, which is weaker than a carbon-carbon double bond, so it has the highest stretching frequency of the three. Therefore, the correct order is 3 < 1 < 2.

Which of the Following Choices Correctly Ranks the Molecules Shown