Here is the chart for the reactivity order. Table l: Sodium lodide in Acetone (5
ID: 695465 • Letter: H
Question
Here is the chart for the reactivity order.
Table l: Sodium lodide in Acetone (5,2) Structure room Precip. forms after 10 min at Precip. after 10 min in warm water bath? Reactivity Rank (1-fastest) Compound 1-chlorobutane 6 min 2-chlorobutane No rxn 2-chloro-2- methylpropane No rxn 1-chloro-2 methylpropane 2.5 min 2-bromobutane 10 min Allyl chloride (TA will demol) 1 sec Table Il: Silver Nitrate in Ethanol (S.1) Precip. forms after 10 min at Precip, after 10 min in Reactivity Rank structure room temp? warm water bath? 1-chlorobutane No Rxn 6 2-chlorobutane No Rxn 2-chloro-2- methylpropane 10 sec 1-chloro-2 methylpropane 8 min 4. 2-bromobutane 30 sec Allyl chloride (TA will demo!) 1 sec
Explanation / Answer
according to the experiment
1-chloro-2-methylpropane is most reactive alkylhalide under SN2 condition and 2-chloro-2-methylpropane is least reactive under SN2 condition.
The SN2 reaction rates of alkyl halides RX , follow the order Allyl> METHYL> 10> 20> 30 . The SN2 reaction is very much less affected by the electrical effects of the group at the reaction centre. Steric effects has considerable influence on the rates of SN2 reaction. The transition state of SN2 pathway is tetrahedrally surrounded , as crowding increases the transition state energy increses and so on reaction rate decreases. that is tertiary substrate i.e. 2-chloro-2-methylpropane is least reactive under SN2 condition, the double bond of allyl chloride increases the stability of the transition state. that is why it is more reactive under SN2 condition.
The rates of SN2 reactions are influenced by the nature of the leaving group. The leaving group ability of halide ions decreases as I- > Br-> Cl-> F- . So. 2-bromobutane is more reactive than 2-chlorobutane.
High temperature increases reaction rate of all the halides by increasing collision frequency.
Polar aprotic solvents like DMF, DMSO are suitable for SN2 reaction. However the reaction rate markledly change from aprotic to protic solvents.
As SN2 reaction rates of alkyl halides RX , follow the order METHYL> 10> 20> 30 1-chlorobutane should be most reactive it is primary halide and do not have bulky group but experiment shows that 1-chloro-2-methylpropane is most reactive among the alkyl halide. This is due to following reason.
In presence of good nucleophile and polar solvent like water 10 alkyl halide i.e. 1-chloro-2-methylpropane is most reactive SN2 reaction, because it do not suffer to much steric hindrance and the transition energy reduced by polar solvent like H2O.