a.Which of the following statements regarding IR spectroscopy is wrong? Infrared radiation is higher in energy than UV radiation. Infrared spectra record the transmission of IR radiation. Molecular vibrations are due to periodic motions of atoms in molecules, and include bond stretching, torsional changes, and bond angle changes. Infrared spectra give information about bonding features and functional groups in molecules. b.Which is the correct order of decreasing wave number of the stretching vibrations of (1) C-H (alkane), (2) C-H (alkene), (3) C-H (alkyne), and (4) C=O? (1) > (2) >(3) >(4) (4) < (3) < (2) < (1) (3) < (4) ≈ (2) < (1) (1) < (4) <(2) < (3) c. To check that a secondary alcohol has been completely oxidised to a ketone you can... check that the IR spectrum has no absorption around 3500cm-1 check that the IR spectrum has absorptions at 3500cm-1 and 1650cm-1 check that the IR spectrum has no absorption around 1650cm-1 check that the IR spectrum no absorptions at 3500cm-1 and 1650cm-1
Spectroscopic Analysis
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Spectroscopic Analysis-1
a.Which of the following statements regarding IR spectroscopy is wrong?
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Infrared radiation is higher in energy than UV radiation. |
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Infrared spectra record the transmission of IR radiation. |
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Molecular vibrations are due to periodic motions of atoms in molecules, and include bond stretching, torsional changes, and bond angle changes. |
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Infrared spectra give information about bonding features and |
b.Which is the correct order of decreasing wave number of the stretching vibrations of (1) C-H (alkane ), (2) C-H (alkene ), (3) C-H (alkyne ), and (4) C=O?
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(1) > (2) >(3) >(4) |
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(4) < (3) < (2) < (1) |
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(3) < (4) ≈ (2) < (1) |
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(1) < (4) <(2) < (3) |
c. To check that a secondary alcohol has been completely oxidised to a ketone you can...
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check that the IR spectrum has no absorption around 3500cm-1 |
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check that the IR spectrum has absorptions at 3500cm-1 and 1650cm-1 |
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check that the IR spectrum has no absorption around 1650cm-1 |
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check that the IR spectrum no absorptions at 3500cm-1 and 1650cm-1 |
d.Proton nmr is useful for investigating the structure of organic compounds because...
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organic compounds contain carbon atoms |
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organic compounds are mostly covalent |
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hydrogen atoms are found in nearly all organic compounds |
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organic compounds have low boiling points |
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it produces a single peak at 10ppm |
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it is inert |
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it is volatile and can be easily distilled off and used again |
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it is used to provide a reference against which other peaks are measured |
f.What is the predicted multiplicity of the indicated protonin the 1H NMR spectrum?
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Septet of triplet |
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quartet of doublet |
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quartet of triplet |
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quartet of setet |
g.In a triplet, the relative peak areas are in the ratio...
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1:1:1 |
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1:2:1 |
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1:3:1 |
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1:4:1 |
h.The proton nmr of 2-bromo-2-methylpropane will consist of...
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three quartets and a singlet |
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two doublets and a singlet |
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two singlets |
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one singlet |
i.Which one of the following pieces of information cannot be obtained from an infra-red spectrum?
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Presence or absence of C=O |
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Presence or absence of O-H |
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The molar mass of the molecule |
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the identity of a compound through comparison with other spectra |
j.The isomer of C4H8 which produces an nmr spectrum with four different signals is...
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CH2=CHCH2CH3 |
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CH3CH=CHCH3 |
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CH3)2C=CH2 |
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cyclobutane |
Hand out:
Experiment 23
Spectroscopic Analysis
PURPOSE
To determine the identity of an unknown using IR and NMR spectroscopy
LEARNING OBJECTIVES
Students will learn to:
- Obtain and analyze Infrared Spectra
- Analyze NMR spectra
READING ASSIGNMENT
Please read the following material in “Laboratory Techniques in
Chapter 21 – Infrared Spectroscopy (Sections 21.1-21.5, 21.7-21.9)
Chapter 22 – Nuclear Magnetic Resonance (Sections 22.4-22.7)
BACKGROUND AND DISCUSSION
In this experiment, students will be assigned an unknown and determine the identity of the unknown using IR and NMR spectroscopic data. There are 20 possible unknowns for this experiment. Students will collect their own IR data using the IR spectrometer. NMR spectra will be provided for the unknown you have been assigned.
Possible Unknowns
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1-propanol
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2-propanol |
methyl ethyl ether
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propanal |
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acetone |
2-butanone |
ethyl acetate |
methyl propanoate |
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2-methyl-benzaldehyde |
2-methyoxy-benzaldehyde |
2-methyl-acetophenone |
2-methoxy-acetophenone |
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3-methyl-benzaldehyde |
3-methoxy-benzaldehyde |
3-methyl-acetophenone |
3-methoxy-acetophenone |
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4-methyl-benzaldehyde |
4-methoxy-benzaldehyde |
4-methyl-acetophenone |
4-methoxy-acetophenone |
The IR spectrum should be used to identify the functional groups present in the molecule using a table of IR absorption bands. The NMR spectrum will provide specific structural data, which should narrow things down to one possible structure.
SAFETY INFORMATION
Many of the organic compounds used in this experiment are flammable. Use gloves and proper eye protection when working with unknown compounds.
PROCEDURE
Obtain an IR spectrum of your assigned unknown. Place 1-2 drops of the unknown solution on one of the salt plates and sandwich them together. Place the salt place in the spectrometer and collect the IR data. Your instructor will provide instructions on data collection, depending upon the equipment available. The salt plates can be cleaned with acetone following use. Obtain a paper copy of a simulated NMR spectrum of your unknown. Use the two spectra to determine the identity of your unknown.
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