Chapter 25.10, Problem 30P

(a)

Interpretation Introduction

Interpretation:

Structural difference between cholic acid and chenodoxycholic acid has to be explained.

(b)

Interpretation Introduction

Interpretation:

Three OH groups of cholic acid is either axial or equatorial has to be identified.

Concept Introduction:

Axial:

The bonding to non-ring atom with $90°$ to the plane of the ring.  Other hand, the bond is perpendicular to the plane of the ring.

Equatorial:

The bonding to non-ring atom with some angle which is small than with the ring plane.  Other words, the bond is parallel to the plane of the ring.