Correct.

No. Try again.

No. That would be a broad absorption around 3300 cm–1. There is no sign of an alcohol or acid here. Try again.

No. That would be much stronger and closer to 1700 cm-1. Try again.

Correct. This appears several places: as medium-strength absorptions at 3070 cm–1 and 1640 cm–1, a strong absorbance at 905 cm–1, and a tell-tale weak absorbance at 1810 cm–1 indicative of a vinyl group, RCH=CH2.

No. The OH absorption is too broad for an alcohol. Try again.

Correct. The extremely strong, broad OH absorption is highly characteristic of a carboxylic acid. In addition, there is indication of a C=O at 1720 cm-1.

No. The absorbance at 1720 cm-1 is not in the correct location for a C=C stretch. Try again.

No. There is no indication of a C–Br stretch around 600 cm–1. Try again.

No. The absorption around 3300 cm–1 is too broad and weak for an alcohol. Try again.

No. The extremely broad OH absorption is too weak to indicate a carboxylic acid. (It is possible that this sample is contaminated by a small amount of a carboxylic acid.) Try again.

No. The spectrum shows no evidence of the presence of a double bond, neither in the 3000–3200 cm–1 region nor in the 1500–1600 cm–1 region. Try again.

No. The absorbance at the 1727 cm–1 peak fits, but what does the absorbance at 2710 cm–1 indicate? Try again.

Correct. The absorbance at 1727 cm–1 indicates a C=O, and the absorbance at 2710 cm–1 is indicative of the C–H stretch associated with the HC=O group.

Chapter 12: Infrared Spectroscopy and Functional Groups

Infrared spectroscopy can answer questions related to bonds and groups of atoms in a compound. For example, examination of an infrared spectrum can often answer questions such as:

These are only a few of the questions that can be answered by inspection of IR spectra. There are many, many characteristic infrared absorptions of functional groups, many of which are listed in the IR section of Appendix VI of your book. Only a small representative sampling of these absorptions is presented in the following table.

Of the functional groups listed, which is (are) evident in the following spectrum?

  

OH of an alcohol

  

C=O of a ketone (1810 cm–1)

  

C=C of an alkene

What information can be gained by inspection of the following spectrum?

  

This compound is an alcohol.

  

This compound is a carboxylic acid.

  

This compound has a carbon–carbon double bond.

  

This compound's molecular formula includes Br.

What information can be gained by inspection of the following spectrum?

  

This compound is an alcohol.

  

This compound is a carboxylic acid.

  

This compound has a double bond.

  

This compound is a ketone.

  

This compound is an aldehyde.