Question

How many stereo-isomers of following compound are predicted by the 2${}^n$ rule?

$C_2{H}_5-\underset{|}{C}H-\underset{|}{C}H-C{H}_3$

$Cl$ $Br$

• A. $2$
• B. $4$
• C. $8$
• D. $16$

Answer 1

The correct option is B $4$

$C_2{H}_5-{\underset{|}{C}}^{\ast }H-{\underset{|}{C}}^{\ast }H-C{H}_3$

$Cl$ $Br$

The 2 chiral $C$ atoms are marked by ${}^{\ast }$

When 2 chiral carbon atoms are present, the number of stereoisomers are $2^n=2^2=4$.

So, 4 stereoisomers are predicted by the $2^n$ rule.