Chem 210 - Sample Exam #4 Solutions

Sample Exams are designed to give you an idea of the types of questions you can expect.  Exam numbers may not exactly agree with currently assigned material, so you may need to examine other sample exams to see questions that might be similar to the upcoming exam. I have made every effort to show correct answers, but there might be an incorrect answer, so if in doubt, you are probably right.

NOTE: All NMR spectra refer to ¹H NMR spectra.

1. Which one of the following compounds is most consistent with the infrared spectrum given in Figure 1? What structural groups are likely responsible for the peaks in the 1500-1600, 3000 and 3400 cm^-1 regions?

a.			b.				c.
	 CH3			 OH				
	 |			 |				-CH2OH
	-C=O			-C=O


Answer: ________
1500-1600 cm-1 peak:	 _______________________________
3000 cm-1 peak:	 _______________________________
3400 cm-1 peak:	 _______________________________

2. What is the most plausible structure for the IR spectrum shown in Figure 2? The empirical formula is C₆H₁₂O. Please also indicate the probable structural group which leads to the peaks near 3000 cm-1 and 1700 cm-1.

Probable structure: _______________________________

3000 cm^-1 peak: _______________________________

1700 cm^-1 peak: _______________________________

6 3. What is the most plausible structure for the IR spectrum shown in Figure 3? The empirical formula is C₆H₁₄O. Please also indicate the probable structural group which leads to the peaks near 3400 and 2800-3000 cm^-1.

Probable structure: _______________________________

3400 cm^-1peak: _______________________________

2800-3000 cm^-1 peak: _______________________________

6 4. The IR and NMR spectra for compound A (C₈H₁₀O) is shown in Figure 4. The numbers above the NMR peaks represents the relative number of protons which give those peaks. Since there are 4 different types of protons, indicate which protons in the structure give rise to each set of peaks.

Probable structure for Compound A:

The IR and NMR spectra for compound B (C₅H₁₀O) is shown in Figure 5. The numbers above the NMR peaks represents the relative number of protons which give those peaks. Since there are 4 different types of protons, indicate which protons in the structure give rise to each set of peaks.

Compound B:

6. Figure 6 presents the NMR spectrum of a hydrocarbon, compound C. The molar mass of compound C is 134 g/mole. What is the structure of this compound?

Compound C:

7. Describe the appearance of the NMR spectrum of each of the following compounds. How many signals would you expect to find, and into how many peaks will each signal split? Indicate the approximate regions that each set of peaks will appear (in the order of Signal Location).

                No. of Signals   Approx. Signal Location        Peaks per Signal

CH3CH2OCH3	_______________  ________________________	______________

CH3CH2OCH2CH3	_______________  ________________________	______________

ClCH2CH2OCH3	_______________  ________________________	______________

ClCH2CClCH2CH3	_______________  ________________________	______________

8. How many signals would you expect to find in the NMR spectrum of each of the following compound? Ignore splitting effect for this problem. (Use blank space to draw structures, showing different hydrogens)

1-Bromobutane __________

2,2-Dibromobutane __________

1,4-Dibromobutane __________

1,1,4-Tribromobutane __________

1,1,1-Tribromobutane __________

9. Each of the following compounds is characterized by a NMR spectrum that consists of only a single peak having the chemical shift indicated. Identify each compound.

C₈H₁₀,  d = 0.9 ppm:

C₆H₁₂,   d  = 1.5 ppm:

C₈H₈,  d = 5.8 ppm:

C₄H₉Br, d = 1.8 ppm:

10. Deduce the structure of each of the following compounds on the basis of the NMR spectra and molecular formulas:

C₈H₁₀

d= 1.2 ppm (triplet, 3H)
d= 2.6 ppm (quartet, 4H)
d= 7.1 ppm (broad singlet, 5H)

C₆H₁₄

d= 0.8 ppm (doublet, 12H)
d= 1.4 ppm (heptet, 2H)

C₄H₆Cl₂

d = 2.2 ppm (singlet, 2H)
d= 4.1 ppm (doublet, 2H)
d= 5.7 ppm (triplet, 1H)

11. Draw the approximate NMR spectrum for p-xylene (CH₃- -CH₃)

12. Give an example when you would use fractional distillation, and why fractional distillation is used in place of simple distillation.

13. What is meant by reflux?

14. Show the balanced equation for the reaction of isopentyl alcohol with acetic acid to produce isopentyl acetate. Then, show the mechanism by which this nucleophilic reaction proceeds.

15. Usually, you use the separatory funnel to extract an organic component into an organic solvent. How can you determine whether the top or the bottom layer is the desired organic layer?

17. Show the reaction by which cyclohexanol is converted into cyclohexene. Include the necessary reactant for this dehydration to occur. Why did you reflux and perform a distillation at the same time?

18. Describe a gas chromatograph. Why do similar compounds (such as bromo- and chloro- derivatives) separate from each other?