Problem Set I: IR Spectroscopy

(covered in class 01/10/2007–01/12/2007) Source: Paula Y. Bruice, Organic Chemistry

1. a) Light of what wavenumber has a wavelength of 4 μm? b) Light of what wavelength has a wavenumber of 200 cm–1?

Source: John E. McMurry, Organic Chemistry

2. Because IR absorptions can be expressed either in micrometers or in wavenumbers, it’s useful to be able to interconvert between units. Do the following conversions:

a. 3.10 μm to cm–1, b. 2250 cm–1 to μm, c. 5.85 μm to cm–1, d. 970 cm–1 to μm.

Source: Paula Y. Bruice, Organic Chemistry

3. Which will occur at a greater wavenumber? a. C–O stretch or C=O stretch? b. C–H stretch or C–H bend? c. ≡C–H stretch or =C–H stretch?

Source: Paula Y. Bruice, Organic Chemistry

4. Assuming that the force constants are the same, which will occur at a greater wavenumber?

a. C–O stretch or C–Cl stretch? b. C–O stretch or C–C stretch?

Source: Paula Y. Bruice, Organic Chemistry

5. Which will occur at a greater wavenumber? Think about resonance forms! a. C–N stretch of an amine or C–N stretch of an amide? b. C–O stretch of phenol or C–O stretch of cyclohexanol? c. C=O stretch of a ketone or C=O stretch of an ester? d. C–O stretch of ethanol or C–O bend of ethanol?

Source: John E. McMurry, Organic Chemistry

6. How would you use IR spectroscopy to distinguish between: a. CH3CH2OH and CH3OCH3?

b. Cyclohexane and 1-hexene? c. CH3CH2COOH and HOCH2CH2CHO (aldehyde)?

Source: Paula Y. Bruice, Organic Chemistry

7. How would you use IR spectroscopy to distinguish between: a. A primary amine and a tertiary amine? b. A cyclic ketone and an open-chain ketone? c. Cyclohexene and cyclohexane?

Source: Paula Y. Bruice, Organic Chemistry

8. Which one of the following compounds has a vibration that is infrared-inactive: acetone, CO2, CO, 1-butyne, 2-butyne, H2, H2O, Cl2, ethene?

Source: John E. McMurry, Organic Chemistry

9. The infrared spectrum of phenylacetylene is shown. What absorption bands can you identify?

Source: Paula Y. Bruice, Organic Chemistry

10. How could you determine by IR spectroscopy that the following reaction had occurred?

OH

O H CH3

OH

Source: John E. McMurry, Organic Chemistry

11. Where might the following compounds have IR absorptions? O

O CH3O

H

Source: Paula Y. Bruice, Organic Chemistry

12. How could you determine the relative strengths of the double bonds in the following compounds?

CH2CH2

Source: John E. McMurry, Organic Chemistry

13. How might you use IR spectroscopy to distinguish among the three isomers 1-butyne, 2-butyne, and 1,3-butadiene?

Source: John E. McMurry, Organic Chemistry

14. Two infrared spectra are shown. One is the spectrum of cyclohexane, the other is the spectrum of cyclohexene. Identify them and explain your answer.

Source: Paula Y. Bruice, Organic Chemistry

15. Which of the following four compounds is responsible for the spectrum given below?

O

O

O

OH

O

HO

Source: Paula Y. Bruice, Organic Chemistry

16. Which of the following five compounds is responsible for the spectrum given below?

OH OH O OH

O

Source: Paula Y. Bruice, Organic Chemistry

17. Which of the following five compounds is responsible for the spectrum given below?

OH OHO O OH OH

Source: Paula Y. Bruice, Organic Chemistry

18. Which of the following five compounds is responsible for the spectrum given below?

O O OH OO

Source: John E. McMurry, Organic Chemistry

19. How might you use IR spectroscopy to distinguish among the three isomers 1-butyne, 2-butyne, and 1,3-butadiene?

Problems from the textbook: 12.1a, 12.2, 12.3, 12.4, 12.5, 12.6, 12.7, 12.8, 12.9, 12.10, 12.11.