1. An O-H stretch occurs at 3650 cm³¹. What is the expected vibrational wavenumber of an O-D bond?

Principles of Modern Chemistry
8th Edition
ISBN:9781305079113
Author:David W. Oxtoby, H. Pat Gillis, Laurie J. Butler
Publisher:David W. Oxtoby, H. Pat Gillis, Laurie J. Butler
Chapter20: Molecular Spectroscopy And Photochemistry
Section: Chapter Questions
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Vibrational Spectroscopy
When an atom in a bond is replaced with a different isotope of the same element, the reduced mass of
the bonded atoms change the absorption of the vibration in the infrared (vibrational) spectrum.
The wavenumber of a vibration is given by v = ¹, where k = force constant of the bond, μ =
2π
reduced mass.
Reduced Mass: μ =
1
"
where m₁ and m2 are the mass of each attached atom.
Assuming the force constant of a particular pair of atoms does not change when one or the other atom
is substituted with an isotope, the magnitude of the vibrational shift can be determined from a ratio of
the two vibrations.
V₁
V₂
1 k₁
2π √1
1 k₂
2π√√1₂
1. An O-H stretch occurs at 3650 cm¹. What is the expected vibrational wavenumber of an O-D bond?
2. An NH3 stretch occurs at 3337 cm¹. At what wavenumber does the ND3 vibration occur?
3. An IR spectrum of a complex containing an Ru-O bond is
depicted to the right. When 0-16 is substituted with 0-18, the
vibration at 887 cm¹ appears to decrease and a new vibration
appears at 841 cm2. Show that this shift is consistent with an Ru-O
bond.
* Prediction based on calculation.
see if the expected shift is consistant with
the calculation
4. The IR spectrum to the right is also of an Ru-O complex
which has been substituted with O-18. Determine the shift
expected for each 0-16 labeled vibration after substitution
with O-18. Do either agree with the new peak und 887
after 0-18 substitution?
30-
36-
1000
1000
'b 887
950
950 900
20
wow
"b887
926
¹941
841
000
800 750 700
Wavenumber (cm)
850 800 750 700
Wavenumbers (cm)
Transcribed Image Text:Vibrational Spectroscopy When an atom in a bond is replaced with a different isotope of the same element, the reduced mass of the bonded atoms change the absorption of the vibration in the infrared (vibrational) spectrum. The wavenumber of a vibration is given by v = ¹, where k = force constant of the bond, μ = 2π reduced mass. Reduced Mass: μ = 1 " where m₁ and m2 are the mass of each attached atom. Assuming the force constant of a particular pair of atoms does not change when one or the other atom is substituted with an isotope, the magnitude of the vibrational shift can be determined from a ratio of the two vibrations. V₁ V₂ 1 k₁ 2π √1 1 k₂ 2π√√1₂ 1. An O-H stretch occurs at 3650 cm¹. What is the expected vibrational wavenumber of an O-D bond? 2. An NH3 stretch occurs at 3337 cm¹. At what wavenumber does the ND3 vibration occur? 3. An IR spectrum of a complex containing an Ru-O bond is depicted to the right. When 0-16 is substituted with 0-18, the vibration at 887 cm¹ appears to decrease and a new vibration appears at 841 cm2. Show that this shift is consistent with an Ru-O bond. * Prediction based on calculation. see if the expected shift is consistant with the calculation 4. The IR spectrum to the right is also of an Ru-O complex which has been substituted with O-18. Determine the shift expected for each 0-16 labeled vibration after substitution with O-18. Do either agree with the new peak und 887 after 0-18 substitution? 30- 36- 1000 1000 'b 887 950 950 900 20 wow "b887 926 ¹941 841 000 800 750 700 Wavenumber (cm) 850 800 750 700 Wavenumbers (cm)
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