Observations for Part B: Silver Nitrate in Ethanol. Deg of Test Tube Alkyl Halid
ID: 1064125 • Letter: O
Question
Observations for Part B: Silver Nitrate in Ethanol. Deg of Test Tube Alkyl Halide Heat in Time Observations substitution g? (YIN) 2-chlorobutane Unreachve N Cloudy nite 20 sec 2-bromobutane 1-chlorobutane unreachve Top acar Bottom cloudy 2 min 1-bromobutane 5 t-butyl chloride N cloudy nhite Isec Ally l 6 crotyl chloride N Cloudy white osec N Cloudy white 12 sec Benzylic 7 benzyl chloride Un reactive Aromatic 8 bromobenzene 9 bromocyclohexane N Cloudy white 30 sec "primary (10), secondary (20), tertiary (30), ally/benzylic, or arylExplanation / Answer
When halides are treated in AgNO3/ethanol, SN1 reaction occurs. In SN1 reaction, a carbocation is formed in the rate determining step. Greater the stability of the carbocation , greater will be the rate of the reaction. The stability order of the carbocation is tert->benzyl>allyl>sec> primary.
An allyl and benzyl carbocation stabilizes a carbocation by resonance. Among the alkyl halides, tertiary carbocation is most stable as, it has greater number of hyper conjugative strucre , followed by secondary carbocation and least stable will be primary carbocation which does not have any hyperconjugative structure.
Thus the rate is highest in test tube 5, then 6 and then 7. No, reaction is possible in 1-chlorobutane (primary) and 2-chlorobutane (secondary).
However primary and secondary alkyl halides can give SN1 reaction if a better leaving group (-Br) is used as observed in test tube 2, 4 and 8.
Bromobenzene does not undergo SN1 reaction as phenyl cation thus formed is very unstable (phenyl cation can not assume a planar structure).
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