Question

Bromo-4-fluorohexane has two chiral carbon atoms; therefore, the maximum number of possible stereoisomers that can be formed is four (determined by using the formula 2n, where n is the number of chiral carbon atoms). draw the four possible stereoisomers of 3-bromo-4-fluorohexane.

Answer 1

Here we have to draw the four isomers of the compound 3-bromo-4-fluorohexane.

The four isomers of the compound is shown in the figure.      

In an organic molecule the chiral -C center is that where four (4) different groups are present. In 3-bromo-4-fluorohexane the 3 and 4 positions are chiral centers. The possible isomers of a molecule can be obtained from the formula 2n. As here 2 chiral centers are present thus number of stereoisomers will be 2×2 = 4.

The four different isomers as shown in the figure are 3R-, 4R-; 3S-, 4S; 3R, 4S and 3S-, 4R- 3-bromo-4-fluorohexane.

In the 3-bromo-4-fluorohexane the functional groups are -Br, C₂H₅, -C₃H₆F and -H for 3-position and -F, -C₂H₅, -C₃H₆ and -H for 4-position respectively.

The priority of the -3 position will be Br > C₃H₆F > C₂H₅ > H and for -4 position F > C₃H₆Br > C₂H₅ > H. If the rotation from the higher priority group to lower is clockwise and anticlockwise then the S- and R- notation are used respectively. However if the -H atom is present at the horizontal position then the notation will be reverse.

Thus the four isomers of the compound is shown.