# Organic Problem Class 7. 2005

The question for this set and its answer are available as Acrobat files. Molecular models corresponding to the various systems are below.

## Question 1. The synthesis of a [16] Mobius Annulene

Total energies (kcal/mol) based on AM1 calculations
A: 245.2 B: 138.1 (=383.3) C: 330.8
D: 262.5 D: 281.2 E: 217.1
E: 216.2 F: 221.9 (Huckel) F: 230.4 (Mobius)
Electrocyclic TS, 4n+2 Electrons, a plane of symmetry
Energy (B3LYP/6-31G*) -464.3514, Huckel aromaticity in 6-ring
NICS(0) -11.1/+0.3 for 6/8 ring (Benzene = -10)
Electrocyclic TS, 4n Electrons, an axis of symmetry
Energy -464.3718 (-12.8 kcal), Mobius aromaticity in 8-ring.
NICS(0) +2.5/-9.5 for 6/8 ring (Benzene = -10)
Electrocyclic TS, 4n+2 Electrons, a plane of symmetry
Energy (B3LYP/6-31G*) -309.5374, Huckel aromaticity in 6-ring
NICS(0) -12.4/+0.2 for 6/4 ring (Benzene = -10)
Electrocyclic TS, 4n Electrons (but the axis of symmetry is only approx)
Energy -309.4782 (+41.8 kcal) Mobius aromaticity in 4-ring.
NICS(0) for +0.4/-5.1 6/4 ring (Benzene = -10)

## Question 2.

Question 2a: For models of the norbornyl cation, see earlier tutorial
Question 2b Initial carbocation: 238.9 kcal/mol First WM shift: 219.0
Second WM shift: 201.3 kcal/mol Third WM shift: 182.3
Fourth WM shift: 163.5 kcal/mol Fifth WM shift: 143.6
Question 2b product Question 2c. Eschenmoser fragmentation
using MeO as a model for TsO.
Question 2c. Proton removed to form anion Epoxide opened. Note linear conjugation of chain.
B3LYP/6-311+G(3d) Transition state for Eschenmoser elimination. -794.7344/-794.7326