Organic:Model answers

Mandatory Examples

• 2.1 Chair: 2.87 kJ, twist-boat 55.49. No pure boat form is normally locatable, although many a text book on organic chemistry implies that it is a true minimum, albeit somewhat higher in energy than the twist-boat. As noted in the references, it is of course a racemisation transition state connecting the two enantiomeric twist-boat forms.
• 2.2 RS/SR = 7.70 (all trans conformation). RR/SS = 6.44 (halogens syn, not anti)
• 2.3
  • 2.3.1 cis-decalin. chair/chair: 17.2. boat/chair: 77.7, boat/boat 131.9
  • 2.3.3 Trans: 14.1, cis 12.9. It appears cis is actually the more stable? Woodward states in his paper that in fact he only isolates 40% of the trans isomer, and comments that the energy difference between cis and trans is likely to be small. So the present result pretty much bears this out!
  • 2.3.4 all-app 29.9, syn 29.7
• 2.4
  • 2.4.1 Axial energies: Me, 12.96, t-Butyl, 77.73, OH, 2.95. Equatorial energies: Me, 2.64, t-Butyl, 32.4, OH, 3.55. The OH appears anomalous in preferring an axial orientation. One presumes the alkoxide will however be heavily solvated, and hence far larger and more akin to t-Butyl.
  • 2.4.4 Thiomethyl, Chair, axial -7.51, equatorial -6.91. Oxamethyl, chair, axial, -2.90, equatorial 1.20
• 2.5 38.5 (obs), 62.8 (unobs)

Additional Examples

• 3.1 Caryophyllene ketone. Trans: 323.9, Cis 334.9
• 3.2 Germacrene. Divinyl trans: 29.44, cis 39.2,
• 3.3 Xestoquinone: Formed isomer, c + (a/b), 139.4 (global minimum?)

• 3.4 Aldol: Ha+Oa, 323.6, Hb+Ob, 45.4. The third possibility is the formation of a cyclopropene.
• 3.5 Hydride reduction of ketone: 7.19(unobs), 0.89 (obs)
• 3.6 NMR: lhs conformation: 32.98 H23 43° (approx 6Hz), H34 160.3° (approx 11.5 Hz) rhs conformation 30.2 H23 43.4° (6 Hz), H34 92° (1Hz)
• 3.7 1-sulfonic acid: 46.6. 2-sulfonic acid 26.2. Wheland intermediate: 1- 29.8. 2- 43.9