Question

How many stereoisomers exist for 1,4 -cyclohexanediol?

Short answer

Answer: There are 4 possible stereoisomers for 1,4-cyclohexanediol.

Step-by-step solution

Identify the chiral centers

Chiral centers are carbons that have four different groups attached and result in non-superimposable mirror images. In 1,4-cyclohexanediol, carbons 1 and 4 are chiral centers because they are connected to four distinct groups (hydroxyl (OH), hydrogen, and two different carbon branches).

Determine stereoisomer possibilities for each chiral center

For each chiral center, there are two possible configurations: R and S. Combining these configurations for both chiral carbons 1 and 4, we have four possible combinations: 1. R configuration at carbon 1 and R configuration at carbon 4 (RR) 2. R configuration at carbon 1 and S configuration at carbon 4 (RS) 3. S configuration at carbon 1 and R configuration at carbon 4 (SR) 4. S configuration at carbon 1 and S configuration at carbon 4 (SS)

Count the stereoisomers

We can count the four possible combinations from Step 2 as distinct stereoisomers. So, there are 4 stereoisomers for 1,4-cyclohexanediol.

Key concepts

Chiral Centers

To understand stereoisomers, one must begin by grasping the concept of chiral centers. These centers, also known as stereocenters, are atoms within a molecule that have four different groups or atoms attached to them, making the molecule non-superimposable on its mirror image, much like your left hand is a non-superimposable mirror image of your right hand.

In organic chemistry, the most common chiral centers are carbon atoms that are bonded to four distinct substituents. This unique bonding environment creates two different spatial arrangements of the atoms, leading to different three-dimensional configurations called enantiomers, which are types of stereoisomers. In the case of 1,4-cyclohexanediol, both carbon atoms at positions 1 and 4 have distinct substituent groups, classifying them as chiral centers and providing the potential for chirality in the molecule.

R and S Configuration

With chiral centers identified, it's crucial to assign their spatial configurations, known as 'R' (from the Latin 'rectus', meaning right) and 'S' (from the Latin 'sinister', meaning left). This nomenclature system is standardized by the Cahn-Ingold-Prelog priority rules, which assign priorities to the substituents attached to a chiral center based on their atomic number. The highest priority group is given the number 1 and the lowest the number 4.

To determine the configuration, one looks at the molecule such that the lowest priority group is oriented away from view. If the remaining substituents decrease in priority in a clockwise manner, the chiral center is assigned as 'R'. If they decrease counterclockwise, it's 'S'. This method helps chemists to accurately describe the spatial arrangement of the molecules. Applying this rule to both chiral centers in 1,4-cyclohexanediol gives us the possible combinations of stereoisomers, vital for understanding the molecule's full structural possibilities.

1,4-Cyclohexanediol

Putting our understanding into practice, consider 1,4-cyclohexanediol. A cyclohexane ring is a six-membered ring notorious for its flexibility and the ability to adopt various shapes, like chairs and boats. The diol part means there are two hydroxyl ('OH') groups attached at carbons 1 and 4 of the ring.

Due to the presence of hydroxyl groups at these positions, and the aforementioned chiral centers at these carbons, 1,4-cyclohexanediol exhibits chiral properties. By combining the possible 'R' and 'S' configurations at the two chiral centers, we see that there are four distinct stereoisomers. Each isomer has different optical properties and could have different biological activities, a point of great interest in fields such as pharmacology. Counting stereoisomers is thus not only academically engaging but also has practical applications in the real world.