Chapter 4, Problem 68P

(a)

Interpretation Introduction

Interpretation:

The configuration of the given structure of citric acid has to be determined.

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.

(b)

Interpretation Introduction

Interpretation:

The chirality of citric acid if ${}^{12}C$ is used instead of ${}^{14}C$ has to be determined.

Concept introduction:

Optical activity of a molecule is the interaction between molecule and plane-polarized light.

Molecule having asymmetric center shows optical activity except mesocompounds.

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