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Question
How do polar solvents help in the first step in SN1 mechanism?
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Solution
The SN1 mechanism proceeds through the formation of carbocation. It involves breaking of C-halogen bond for which energy is obtained through the salvation of halide ion with the proton of the protic solvent. Thus, polar solvents help in ionisations step by stabilizing the ions by solvation.
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| (I) |  |
| (II) |  |
| (III) |  |
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| Column I | Column II | |
| (i) |  |
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| (ii) | \[\begin{array}{cc} \ce{CH3 - CH = CH2 + HBr -> CH3 - CH - CH3}\\ \phantom{............................}|\phantom{}\\ \phantom{.............................}\ce{Br}\phantom{} \end{array}\] |
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| (iii) |  |
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| (iv) |  |
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| (v) | \[\begin{array}{cc} \ce{CH3 CH2 CH CH3 ->[alc.KOH] CH3 CH = CH CH3}\\ \phantom{}|\phantom{..........................}\\ \phantom{}\ce{Br}\phantom{........................} \end{array}\] |
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\[\begin{array}{cc}\ce{CH3CH2CHCH3}\\
\phantom{.....}|\\
\phantom{......}\ce{Br}\\
\end{array}\] or \[\begin{array}{cc}\phantom{.......}\ce{CH3}\\
\phantom{...}|\\
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\phantom{...}|\\
\phantom{.......}\ce{CH3}\\
\end{array}\]
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(i) \[\begin{array}{cc}
\phantom{}\ce{\underset{}{(CH3)2CH - CH2Br} ->[C2H5OH] \underset{}{(CH3)2CH - CH2OC2H5 + HBr}}\\
\end{array}\]
(ii) \[\begin{array}{cc}
\phantom{}\ce{\underset{}{(CH3)2CH - CH2Br} ->[C2H5O-] \underset{}{(CH3)2CH - CH2OC2H5 + Br-}}\\
\end{array}\]
The mechanisms of reactions (i) and (ii) are respectively:
