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Chapter 16: Ethers, Epoxides and Sulfides |  |
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Chapter 16: Ethers, Epoxides and Sulfides | |
| Qu1: | Ethers are cleaved by strong acids like HBr and HI to give an alcohol and an alkyl halide. |
| However, in the presence of excess HI, alcohols react to give alkyl
iodides.
(a) 2 moles CH3CH2I (b) (CH3)3CI and CH3I (c) I-CH2CH2CH2CH2-I (d) I-CH2CH2-I |
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| Qu2: | The challenge is the synthesis of the ether from toluene. First question, how do we make ethers ? |
A Williamson ether synthesis requires and alkoxide and an alkyl halide.
In this case, it is necessary to make the alcohol from the halide by a
simple substitution since the halide can be obtained from the toluene
via a radical substituion. The retrosynthesis and the synthesis are shown
below:
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| Qu3: | In an SN2 process we normally get inversion, and in SN1 racemisation. |
Since we don't have racemisation it can't be SN1, so it must be SN2.
In order to get overall retention, this could indicate 2 sequential SN2
reactions. The process is that the 1,2-halohydrin forms an epoxide via
an intramolecular SN2 displacement of chloride, followed by ring opening
of the epoxide under basic conditions via another SN2 reaction.
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