conformers

Question 1

Are all staggered conformations same in energy?

Answer 1

No

• staggered anti conformer most stable ( when bulky sub. 180 degrees apart)
• staggered gauche more unstable/higher in energy (when bulky substituents very close to each other)

Question 2

as a flat molecule is cyclopentane or cyclohexane more stable?

Answer 2

cyclopentane is more stable as the bond angles are smaller than the large bond angles of cyclohexane

• cyclopentane is slightly greater than the ideal bond angle of 109.5
• cyclohexane is MUCH greater than 109.5

Question 3

why in reality is cyclohexane very stable?

Answer 3

• molecules can twist/rotate their bonds to reduce angle strain/torsional strain
• cyclohexane can go into a chair conformation to relieve torsional strain and angle strain - the atoms pinch in together to decrease the bond angle
• the angles become 109 degrees

Question 4

why would it be better for cyclopentane to be in a envelope/puckered position when angle strain is already pretty good in flat form?

Answer 4

• although angle strain is quite good in flat form torsional strain is HUGE
• envelope form has increase angle strain but much less torsional strain T.F good compromise

Question 5

what are the rules of ring flip?

Answer 5

Up stays up and down stays down