1. One should always carefully consider which solvent to choose for a reaction.
ID: 961912 • Letter: 1
Question
1. One should always carefully consider which solvent to choose for a reaction. Which of the following solvents are inappropriate for the reduction of an ester using lithium aluminum hydride (LiAlH4)? (Select all correct answers for full credit.)
A) Tetrahydrofuran B)Water C)Ethanol D) Diethyl Ether
2. Shown below is the IR spectrum of the product obtained from the reduction of cyclopentanone. Which of the following statements about this particular reduction reaction is true?
A) One can not conclude anything about the reduction from the infrared spectrum shown. The product is obvously "wet" and contains methanol, ethanol, or water
B) The strong absorption near 1700 wavenumbers and the absence of strong absorption centered at 3300 wavenumbers indicated the reduction was a dismal failure.
C) The reductions was ony partially compleate becasue 1) the strong absorption at 2800-3000 wavenumbers is due to the O-H stretch in the product and 2) the strong absorption number near 1700 wavenumbers is due to the C=O group in the starting material.
3. Which of the following may be a potential drawback when reducing aldehydes or ketones using lithium aluminum hydride, LiAlH4? (Select all correct answers for full credit.)
A) potentially violent reactions with ether and tetrahydrofuran
B) reduction of aromatic rings to cyclohexane
C) reduction of other functional groups that may be present
D) potentially violent reactions with moisture
Explanation / Answer
1. B)Water C)Ethanol
Because lithium aluminum hydride is highly reactive towards proton (H+) releasing substances and displaces hydrogen from water and alcohol.
2. C) The reductions was ony partially compleate becasue 1) the strong absorption at 2800-3000 wavenumbers is due to the O-H stretch in the product and 2) the strong absorption number near 1700 wavenumbers is due to the C=O group in the starting material.
3. C) reduction of other functional groups that may be present
sodium borohydride does not reduce amide functional group, but lithium aluminum hydride does. lithium aluminum hydride is a powerful reducing agent than sodium borohydride for this reason specific functional group transformation can be acieved by sodium borohydride in presence of other functional groups.
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