Question

111111 Juana Scott monitored the rate of the reaction of sodium ethoxide with 2-bromo-2-methyl hexane and with 2-fluoro-2-methyl hexane, The reactions were carried out in two respectively in hexane (CH). different, solvents and at two different concentrations as shown in the table below. King James inspired by the work of JS tried the reaction of 2-Bromobutane and 2-fluorobutane with sodium ethoxide under similar reaction conditions used by Dr. Scott. Rate Solvent JS EXPT. (NaOet) {R-X) 10/sec Hexane X - Br 0.1 0.1 M M 2000/sec Br Formic acid 0.1 0. M 1 M 4000/sec Formic acid 0.2 M 0.1 M 2000/sec 0.1 M 0.2 Formic acid M 200/sec 0.1 M 0.1 formic acid. M 100/sec 0.1 M 0.1 Hexane M KJ EXPT. Rate {R-X) {NaOEt} Solvent 0.1 5000/sec M 0.1 M Hexane 0.1/sec 0.1 Formic acid M 0.2 M 0.1 M Hexane 20000/sec X = Br 0.1 M 0.2 M Hexane 20000/sec X = F 0.1 M 0.1 M Hexane 4950/sec F 0.1 M Formic acid 0.09/sec Which chemist will report an effect of the leaving group, on the rate of the reaction? (a) JS (b). KJ (c) Both (d) Neither Whose reaction is likely a second order reaction? (a) JS (b) KJ (c) Both (d) Neither 0.1 M X = Br 0.1 M 1. Whose experiment was independent of the concentration of sodium? (a) JS (b) KJ (c) Both (d) Neither Whose experiment probed the influence of the nucleophile? (a) JS (b) KJ (c) Both (d) Neither Whose experiment most probably gave optical rotation of -10°C? (a) JS (b) KJ (c) Both (d) Neither 6. whose experiment will be favored if done in ethanol as a solvent? (a) JS (b) KJ (c) Both (d) Neither The rate constant for JS's reaction is? 7.

Answer 1

1) a) JS chemist report an effect on the leaving group on the rate of the reaction.

By comparing the Expt 1 and Expt 6 shows that if the leaving group is F then the rate of the reaction increased by 10 times in hexane solvent, Expt 2 and Expt 5 shows that if the leaving group is F then the rate of the reaction decreased by 10 times in case of formic acid solvent.

Whereas KJ expt does not show any change in rate of the reaction when leaving group changes.

2) b) KJ is second order reaction.

Compare expt 2 and 3 when NaOEt concentration kept constant and R-X concentration doubled, rate doubled, expt 3 and 4 when R-X concentration kept constant and NaOEt concentration doubled, no change in rate of the reaction. This shows that rate of the reaction depends on concentration of R-X only and so First order reaction (S_N¹).

Compare expt 8 and 10 when NaOEt concentration kept constant and R-X concentration doubled, rate increased by four-fold, expt 8 and 11 when R-X concentration kept constant and NaOEt concentration doubled, again rate of the reaction is increased by four-fold. This shows that rate of the reaction depends on concentration of both R-X and NaOEt and so second order reaction (S_N²).

3) a) JS

Compare expt 2 and 3 when NaOEt concentration kept constant and R-X concentration doubled, rate of the reaction gets doubled, expt 3 and 4 when R-X concentration kept constant and NaOEt concentration doubled, no change in rate of the reaction. This shows that rate of the reaction depends on concentration of R-X only and independent of concentration of sodium ethoxide.

4) d) KJ

Though the rate of the reaction of KJ expt depends on NaOEt (Nucleophile) based on the experimental data given.

Compare expt 8 and 10 when NaOEt concentration kept constant and R-X concentration doubled, rate increased by four-fold, expt 8 and 11 when R-X concentration kept constant and NaOEt concentration doubled, again rate of the reaction is increased by four-fold. This shows that rate of the reaction depends on concentration of both R-X and NaOEt and so second order reaction.

5) b) KJ

Inversion of configuration major product. Whereas for JS expt both retention and inversion of configuration is obtain.

6) a) JS

S_N¹ is favoured in presence of polar protic solvents (Eg. Ethanol)

7) Rate for JS reaction = -k[R-X]

Where k is rate constant

[R-X] - concentration of the reactant.