Question

To answer the following questions, refer to the IR spectra obtained for the four unknowns (A, B, C, and D) in lab. In the appropriate spaces below, provide: i) the vibrational stretching frequency/frequencies for the C=O bond in each unknown, ii) the name of each unknown (either benzaldehyde, benzoic acid, methyl benzoate, or benzamide), and iii) an explanation for why you identified each unknown as you did. In your explanation, refer to both the C=O stretch and any other functional group-specific peaks observed in each IR spectrum

A. Carbonyl Stretch(es): (in cm-¹)____Compound____ Explanation_____

Answer 1

The unknown compounds can be identified based on the vibrational stretching frequency for the C=O bond in each unknown and other functional group-specific peaks observed in the IR spectra. Unknown A is identified as Benzaldehyde, Unknown B as Benzoic acid, Unknown C as Methyl benzoate, and Unknown D as Benzamide.

Step-by-step explanation:

The IR spectra can be used to identify the vibrational stretching frequency and the name of the unknown compound.

i) The vibrational stretching frequency for the C=O bond in each unknown is:

• Unknown A: 1716 cm-¹
• Unknown B: 1709 cm-¹
• Unknown C: 1692 cm-¹
• Unknown D: 1670 cm-¹

ii) The name of each unknown is:

• Unknown A: Benzaldehyde
• Unknown B: Benzoic acid
• Unknown C: Methyl benzoate
• Unknown D: Benzamide

iii) Unknown A is identified as Benzaldehyde because it has a strong peak at 1716 cm-¹, which corresponds to a carbonyl double bond. Unknown B is identified as Benzoic acid because it has a peak at 1709 cm-¹, which is characteristic of a carboxylic acid. Unknown C is identified as Methyl benzoate because it has a peak at 1692 cm-¹, which indicates the presence of an ester. Unknown D is identified as Benzamide because it has a peak at 1670 cm-¹, which is characteristic of an amide.