Reaction of methoxide ion with the Z- and E-isomers of O-methylbenzohydroximoyl cyanide. Theoretical calculations on the conformations of the tetrahedral intermediate
✍ Scribed by James E. Johnson; Issam Jano; Michael A. McAllister
- Publisher
- John Wiley and Sons
- Year
- 1999
- Tongue
- English
- Weight
- 93 KB
- Volume
- 12
- Category
- Article
- ISSN
- 0894-3230
No coin nor oath required. For personal study only.
✦ Synopsis
31 G*) were carried out on the tetrahedral intermediate RC(CN)(OCH 3 )-NOCH 3 À
, where R = C 6 H 5 , CH 2 =CH or H, generated by nucleophilic attack of methoxide ion on (Z)-or (E)-O-methylhydroximoyl cyanide [RC(CN)=NOCH 3 ]. These calculations indicate that the staggered conformation 4C, which would lead to an E-substitution product, is approximately 7 (R = H) or 8 kcal mol À1 (R = CH 2 =CH) less stable than conformation 4A, which leads to a Zsubstitution product. Furthermore, the lowest energy transition state leading to a Z-substitution product is approximately 5 kcal mol À1 lower in energy than the lowest energy transition state leading to an E-substitution product. These results provide an explanation for the experimental results reported recently that (Z)-O-methylbenzohydroximoyl cyanide gives only the less thermodynamically stable Z-substitution product under conditions where the purported tetrahedral intermediate should have a long enough lifetime to establish an equilibrium between all the staggered conformations.