Complete the skeleton below to show the following structure: (1R,2R,5S)-2-bromo-5-ethylcyclohexanol. (6 Marks)
The Correct Answer and Explanation is:
To complete the skeletal structure of (1R,2R,5S)-2-bromo-5-ethylcyclohexanol, start by identifying the base molecule: cyclohexane, which is already provided.
Step-by-Step Completion:
- Number the cyclohexane ring:
Assign carbon 1 to the carbon bearing the hydroxyl (-OH) group. Number the ring clockwise to give the lowest possible locants to the substituents at positions 2 and 5. - Add substituents:
- At C1: Attach the hydroxyl group (-OH) with R configuration. In a chair conformation, the equatorial position is generally more stable, but stereochemistry determines orientation. The R configuration here will place the OH axial up if the viewer assigns priorities accordingly.
- At C2: Attach a bromine atom (Br) with R configuration. Based on stereochemistry rules, this places the Br group equatorial down.
- At C5: Attach an ethyl group (-CH₂CH₃) with S configuration, which typically goes axial down.
- Maintain 3D stereochemistry:
Use solid wedges (coming out of the plane) and dashed wedges (going behind the plane) to indicate chiral centers:- C1: OH on a solid wedge up
- C2: Br on a solid wedge down
- C5: Ethyl group on a dashed wedge down
Final Answer Description:
- The ring is cyclohexane.
- OH group is on carbon 1 with R configuration (solid wedge).
- Br is on carbon 2 with R configuration (solid wedge or placed to reflect spatial orientation).
- Ethyl group is on carbon 5 with S configuration (dashed wedge).
This ensures the structure reflects the stereochemistry (1R,2R,5S) and matches the molecular name 2-bromo-5-ethylcyclohexanol. The skeletal structure should be a proper 3D representation with appropriate wedges to reflect chirality.
