JEE Main · 2012 · 29 Apr 2012 · Offline · General Organic Chemistry

2-methylbutane is $\mathrm{C}{\mathrm{H}}_3-\mathrm{CH}(\mathrm{C}{\mathrm{H}}_3)-\mathrm{C}{\mathrm{H}}_2-\mathrm{C}{\mathrm{H}}_3$, and replacing one hydrogen by chlorine can happen at four distinct sites. Substituting on either of the two equivalent methyls attached to C-2 gives $\mathrm{ClC}{\mathrm{H}}_2-\mathrm{CH}(\mathrm{C}{\mathrm{H}}_3)-\mathrm{C}{\mathrm{H}}_2\mathrm{C}{\mathrm{H}}_3$, whose C-2 now carries four different groups and is a stereocentre. Substituting on the C-3 methylene gives $\mathrm{C}{\mathrm{H}}_3-\mathrm{CH}(\mathrm{C}{\mathrm{H}}_3)-\mathrm{CHCl}-\mathrm{C}{\mathrm{H}}_3$, whose chlorinated carbon is also a stereocentre. The other two products — chlorination at the tertiary C-2 and at the terminal C-4 methyl — each leave a carbon bearing two identical methyl groups and so are achiral. Thus two of the monochlorination products are chiral.