CHM 234: Worksheet #13
Chapter 10
Spring 2011
Dr. Halligan
The “-OH” group makes a “lousy LG” and so we use the following regents to convert an alcohol
to a more reactive substrate for future substitution and elimination reactions.
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HI, HBr or HCl with ZnCl (SN1 mech for 2° and 3° ROH, SN2 mech for 1° ROH)
PBr3, PCl3 or SOCl2 (all with pyridine) (Used with 1° and 2° ROH, SN2 mech, get RX
product)
TsCl, MsCl, or TfCl (all with pyridine) (Used with 1° and 2° ROH, Results in an OTs,
OMs or OTf LG, then subsequent SN2 reactions provide substitution products).
1. Write a mechanism leading to the major product of each of the following reactions. Keep in
mind that 1° alcohols undergo SN2 reactions and 2° and 3° alcohols proceed by the SN1
mechanism.
2. PCl3, PBr3, PI3 and SOCl2 are used to convert 1° and 2° alcohols to alkyl halides. Write a
mechanism and give the major product of each of the following reactions.
3. Show how to convert trans-4-methylcyclohexanol to cis-1-iodo-4-methylcyclohexane via a
tosylate. Write a mechanism for this transformation and use the chair form of the
cyclohexane derivatives.
4. Design a synthesis for the following compounds from 1-butanol. Show all reagents and
intermediates. In order to maximize yields, first convert the alcohols to either alkyl halides
by PCl3, PBr3, PI3 and SOCl2 or convert them to sulfonate esters by TsCl, MsCl or
trifluoromethanesulfonyl chloride.
5. Alcohols can be dehydrated by concentrated acid to give alkenes (prone to carbocation
rearrangements). However, 1° and 2° alcohols are especially problematic since side since
side reactions occur so we typically use POCl3 to convert OH to a better LG and then
conduct an E2 reaction with pyridine as the base. Propose a mechanism for each of the
following reactions.
6. Predict the products of the following oxidation reactions.
7. Ethers are typically cleaved by an SN1 mechanism unless a stable carbocation cannot be
formed, then they proceed via an SN2 mechanism. Write mechanisms for the following
reactions that involve ethers and 1 equiv. of HI.