GENERAL CHEMISTRY WORKSHOP

SPECTROSCOPY

1. A sample of steel from a bicycle frame is to be analyzed to determine its manganese

content. A sample of the steel weighing 0.1523 g was dissolved, and the unknown amount of manganese was converted to MnO4

-1. Water was then added to give a solution with a final volume of 100.0 mL. A portion of this solution was placed in a spectrophotometer, and its absorbance was found to be 0.780 in a 1.00 cm cuvette. Given that ε for MnO4

-1 in aqueous solution is 2.48 x 103 L/mol · cm, calculate the percent manganese in the steel.

2. The molar extinction coefficient of lysozyme at a pH of 6.1, for an incident frequency

of 1645 cm-1, is 2.0 x 104 L mol-1 cm-1. An aqueous solution containing 80. mg/mL of this enzyme has an 8.3% transmittance at 1645 cm-1 in a cuvette of 0.100 mm light path. What is the approximate molar mass of lisozyme?

3. The absorption of ultraviolet light of wavelength 280 nm by proteins is caused almost

entirely by the aromatic amino acids tryptophan and tyrosine. Suppose that a protein of molar mass of approximately 26,000 amu contains two residues of tryptophane (εtry = 5.0 x 103 L mol-1 cm-1) and six residues of tyrosine (εtyr = 1.1 x 103 L mol-1 cm-1). The absorbance is recorded from a cuvette of 1.00 cm path length, holding the protein concentration at 1.00 mg/mL. Calculate the absorbance and the percent transmittance of this solution at 280 nm.

4. Absorption by H35Cl occurs near 200. cm-1, and the spacing between neighboring

lines is 20.89 cm-1. Find the moment of inertia and the internuclear distance in H35Cl. 5. The infrared spectrum of X16O shows the υ = 0 to υ = 1 transition at 1877 cm-1. If the

force constant of X16O is 1550. N m-1 and the atomic mass of 16O is 15.9995 amu, determine the identity of the isotope X.

6. Draw the idealized NMR spectra for the following compounds: a) CH2Cl2, b) CH3-CHI2,

c) CH2F-CO-CHBr2, d) CH3 -O- CH3, e) CH2=CBr-CH3.

7. Draw the idealized NMR spectra for the following compounds. (Assume that the five hydrogen atoms in the benzene are equivalent with no spin-spin coupling)

8. Draw the idealized NMR spectra for the following compounds: a) bromoethane, b) 2-butanone, c) ethylmethyl ether, d) toluene, (Assume that the five hydrogen atoms in the benzene are equivalent with no spin-spin coupling), e) methyl acetate.

9. Draw the idealized NMR spectra for the following compounds: a) CH3CH2CH2Br,

b) CH2=CHCH2CH3, c) CH3CH2-O-CH2CHFCH3. 10. The NMR spectra below are for the alkene C6H12 and for the alkane C4H10O. Deduce

the structures for these compounds. Please notice that the TMS reference has been omitted in each spectrum.