Monochlorination of 2-methylbutane in light is carried out with relative reactivities per hydrogen $1^{\circ} : 2^{\circ} : 3^{\circ} = 1 : 3.8 : 5.0$ . Stereoisomers of one constitution are counted together as one product. What percentage of the total monochloro product is chiral (contains a stereocentre)? Give the answer to the nearest integer.

Numerical answer type, tolerance 0.5.

Answer: 63

2-Methylbutane has 6 H on the two C2 methyls, 3 H on C4, 2 H on C3 and 1 H on C2. The chiral products are 1-chloro-2-methylbutane (from the 6 C1-type H, stereocentre C2) and 2-chloro-3-methylbutane (from the 2 C3 H, stereocentre C2). The yields are

6 \times 1 = 6.0

and

2 \times 3.8 = 7.6

. The total is

9 + 7.6 + 5.0 = 21.6

. Chiral fraction

= 13.6/21.6 \times 100 = 63.0

, which is 63 per cent.

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