Drawing the Three-Dimensional Structure of an Enantiomer

Draw a tetrahedral representation of (R)-2-chlorobutane

S t r a t e g y

Begin by ranking the four substituents bonded to the chirality center: (1) –Cl, (2) -CH_2CH_3, (3) – CH _{3}, (4) –H. To draw a tetrahedral representation of the molecule, orient the lowest-ranked group (–H) away from you and imagine that the other three groups are coming out of the page toward you. Then place the remaining three substituents such that the direction of travel 1 → 2 → 3 is clockwise (right turn), and tilt the molecule toward you to bring the rear hydrogen into view. Using molecular models is a great help in working problems of this sort.