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Assignment UV-VIS 1. The Ultraviolet spectrum of benzonitrile shows a primary absorption band at 224nm and a secondary band at 271nm. a. If a solution of benzonitrile in water with a concentration of 1x 10 -4 molar, is examined at a wavelength of 224nm, the absorbance is determined to be 1.30. the cell length is 1cm. What is the molar absorptivity of this absorption band? b. If the same solution is examined at 271nm, what will be the absorbance reading ( =1000)? What will be the intensity ratio I ɛ o/I? 2. The UV spectrum of acetone shows absorption maxima at 166, 189 and 279nm. What type of transition is responsible for each of these bands? 3. Chloromethane has an absorption maximum at 172nm, bromomethane shows an absorption at 204nm, and iodomethane shows a bond at 258nm. What type of transition is responsible for each band? How can the trend of absorptions be explained? 4. Which of the following compounds would you expect to have a - ππ * UV absorption in the 200 to 400 nm range? (CH3)2C=C=O 5. Would you expect allene, 2HC=C=CH2, to show a UV absorption in the 200 to 400 nm range? Explain? 6. Which of the following compounds would you expect to show UV absorptions in the 200 to 400nm range? 7. Arrange the following molecules according to the wavelength that they would absorb (from lowest to highest) in the UV VIS spectra. Explain your answer. a. CH 2 =CHCH=CH 2 b. CH 3 CH 2 CH 2 CH=CH 2 c. CH 2 =CHCH=CHCH=CH 2 d. CH 2 =CHCH 2 CH 2 CH=CH 2
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Assignment UV-VIS
1. The Ultraviolet spectrum of benzonitrile shows a primary absorption band at 224nm and a secondary band at 271nm.
a. If a solution of benzonitrile in water with a concentration of 1x 10-4 molar, is examined at a wavelength of 224nm, the absorbance is determined to be 1.30. the cell length is 1cm. What is the molar absorptivity of this absorption band?
b. If the same solution is examined at 271nm, what will be the absorbance reading (ɛ=1000)? What will be the intensity ratio Io/I?
2. The UV spectrum of acetone shows absorption maxima at 166, 189 and 279nm. What type of transition is responsible for each of these bands?
3. Chloromethane has an absorption maximum at 172nm, bromomethane shows an absorption at 204nm, and iodomethane shows a bond at 258nm. What type of transition is responsible for each band? How can the trend of absorptions be explained?
4. Which of the following compounds would you expect to have a π-π* UV absorption in the 200 to 400 nm range?
(CH3)2C=C=O
5. Would you expect allene, 2HC=C=CH2, to show a UV absorption in the 200 to 400 nm range? Explain?
6. Which of the following compounds would you expect to show UV absorptions in the 200 to 400nm range?
7. Arrange the following molecules according to the wavelength that they would absorb (from lowest to highest) in the UV VIS spectra. Explain your answer.
a. CH2=CHCH=CH2
b. CH3CH2CH2CH=CH2
c. CH2=CHCH=CHCH=CH2
d. CH2=CHCH2CH2CH=CH2
8. Determine which molecule would have the longer wavelength of absorption and why?
a. CH2CHCH2CH2COCH3
b. CH3CH2CH=CHCOCH3
9. State the two primary UV-Vis excitations and give an example for each.10.An energy of approximately 340 kJ mol-1 is needed to excite an electron in
compound X. Can UV-Vis spectrometry be used to experimentally measure compound X?
11. Consider the following compounds and state which compounds can be detected using UV-Vis spectrometry and whether you would expect any shift in the position of λmax.
a.
b.
c.
d.
