Chemical Kinetics and Nuclear ChemistryHard

Question

When secondary alkyl halide undergoes SN reaction, it follows SN1 (first-order) and SN2 (second-order) pathway simultaneously. The dominant pathway depends on large number of factors. An alkyl halide undergoes both pathway with rate constants 3 × 10−4 s−1 and 5 × 10−4 M−1 s−1, respectively. Which of the following is/are correct information for the reaction?

Options

A.If the concentration of nucleophile is 0.1 M, then the dominant pathway of reaction isSN1.
B.If the concentration of nucleophile is 1.0 M, then the dominant pathway of reaction is SN2.
C.The percentage of SN1 product will be 50, when the nucleophile concentration is 0.6 M.
D.The percentage of SN1 product will be 40, when the nucleophile concentration is 0.9 M.

Solution

For SN1 path: r1 = (3 × 10–4 s–1) [RX]

For SN2 path: r2 = (5 × 10–4 M–1 s–1) [RX]

(a) = 0.1 M, then r1 > r2

(b) = 1.0 M, then r1 < r2

(c) = 0.6 M, then r1 = r2

(d) = 0.4 M, then $\frac{r_{1}}{r_{2}} = \frac{2}{3}$

∴ Percentage product by SN1 = $\frac{2}{2 + 3} \times 100\% = 40\%$

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