Unit 2 - Conformations Flashcards
Why do different conformations occur?
Rotation about bonds
Which is the highest energy conformation? Why?
Eclipse. Unfavourable interactions between close together groups.
Which is the lowest energy conformation? Why?
Staggered. All of the groups are as far apart as possible, therefore unfavourable interactions are reduced.
What are gauche interactions? What is their relative energy?
Unfavourable interactions between larger molecules in a staggered conformation. Depending on the group and interaction, they are more favourable than eclipse but less favourable than perfect staggered.
What happens to axial groups in a ring flip?
They become equatorial
Why do groups prefer to be equatorial in a chair conformation?
When they are axial they have unfavourable gauche interactions between axials Hs. 1,3 diaxial clashes
What is the smallest ring size and why is it so unstable?
3 membered rings, very strained 60 degrees bond angle
How many conformations are there for trans decalins and why?
Only one single conformation because the rings are both equatorial and opposite each other
Which is the more stable decalin?
Trans, cis decalins have an axial group which is higher in energy
What type of conformations do epoxides form?
Half chair.
