Chapter 4, Problem 67P

(a)

Interpretation Introduction

Interpretation:

The number of stereoisomers present in given structure of ephedrine has to be determined.

Concept introduction:

Stereoisomers are isomers which have different spatial arrangement in spite of same bond connectivity.  Stereoisomers are due to the presence of stereocenter.

Asymmetric center is a stereocenter which arises to hydrocarbons if the carbon is bonded to four different groups.

The equation for finding Stereoisomers from number of asymmetric centers in compounds is $2^n$, in which ‘n’ is the number of asymmetric centers.

(b)

Interpretation Introduction

Interpretation:

The configuration of each of asymmetric centers has to be given.

Concept introduction:

According to Cahn-Ingold-Prelog system,

The group attached to asymmetric center should be ranked based on the atomic number of atom which directly connected to asymmetric center.  The higher the atomic number of atom, higher the priority.  If there is tie, then consider the next atoms attached to the connected atom and so on.

Check the direction of arrow drawn in the direction of decreasing priority.  If the arrow points clockwise direction, then the compound has R configuration.  If the arrow points counterclockwise direction, then the compound has S configuration.  If the group with lowest priority is not bonded by a hatched wedge, then interchange this group (lowest priority) by group bonded to hatched wedge and draw the arrow in priority order but the configuration is assigned as just reverse.