Take the relative reactivities per hydrogen for $Cl X_{2}$ at 25 $^{\circ}$ C as primary : secondary : tertiary = 1 : 3.8 : 5. The alkane shown is monochlorinated at 25 $^{\circ}$ C. What percentage of all monochloro products is chiral (nearest whole number)?

Answer: C

The alkane is pentane. Weights: C-1/C-5

6 \times 1 = 6

; C-2/C-4

4 \times 3.8 = 15.2

; C-3

2 \times 3.8 = 7.6

; total 28.8. Only 2-chloropentane has a stereocentre (1-chloropentane and 3-chloropentane are achiral), so the chiral share is

15.2/28.8 = 52.8%

, about 53%.