Chemistry - STEREO ISOMERISM Question with Solution | TestHub
Identify the chair or boat six-membered rings in the following structures and say why that particular shape is adopted.
Options:
Answer:
Solution:
The first three are relatively simple :
1st structure : a simple chair with all substituents equatorial - the chair is strain-free and the substituents choose equatorial positions.
2nd structure : a boat locked in the cage molecule with no choice - a chair is impossible because the one-atom bridge holds the two bridgehead carbons close together.
3rd structure : a chair inside a cage molecule with some choice - the starred carbon can move, so the six-membered ring adopts the chair.
The next two have several rings each, all boats in the first of them (the bicyclo[2.2.2] cage has three boat rings and no choice); the sixth molecule also has a boat (norbornane contains one boat ring) and neither cage has any choice.
The rings are all chairs in the fifth molecule, adamantane - a tiny fragment of the diamond lattice. The rings do not all look very chair-like in flat diagrams; making a model is the only way to appreciate this beautiful, symmetrical structure and to see all four chairs.
