Question

Problem #9. In addition to the chair conformations, cyclohexane derivatives also have half-chair, twist boat, and boat conformations. These are all higher energy than chair conformations. In fact, the half- chair is the transition state between the chair and the twist boat, and the boat is the transition state between two different twist boat conformations. See p. 201 - 203 of your textbook for a detailed discussion. Cyclohexane Chair Flip Energy Diagram half chair (10 kcal/mol) half chair (10 kcal/mol) boat (6.5 kcal/mol) kcal/mol 6 twist boat 5.5 kcal/mol twist boat 5.5 kcal/mol chair chair a) Why do you think the half-chair structures are so high in energy? Is it because of angle strain or torsional strain, or both? b) The boat structure has angle strain, torsional strain, and an additional destabilizing interaction that the other cyclohexane conformations do not have. Describe this additional destabilizing interaction. A drawing may help.

Answer 1

W WWWASSA eclipsed e-c bord A angle 120 I H (1) Tho eclipped C-C Creates the torsional Sorment strain . (2) Bond angle (e-c-e) > 10994" creates angle strain which is also found in half chair form I (3) Half chair has least amount of symmetry eclipsed Half Chair conformatim Those three reasons stable conformation . Half chair is tard least or for exclohexane. - flagpole Hydrogen Interaction H Apart from torsimal strain and angle strain there is another destabilizing energy in boat ostenatting conformation which is a fagpole o hydrogen interaction. This is a one kind of sterie interaction which makes system destabilize.