Conformação e Mecanismo de Trans-Decalinas

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Chapter 18 Suggested solutions for Chapter 18 139 Purpose of the problem Exploration of the relationship between conformation of important trans-decalins and mechanism. Suggested solution mechanism is easy and the conformations of trans-decalins are fixed, so we can start with the Me Me Br H Br H Only the first compound can get the necessary 'attack from the back' angle of 180° between deophile (O⁻), carbon atom, and leaving group (Br) for the intramolecular SN2 reaction to make epoxide. Me oH Me H Br H Br Problem 7 Draw conformational diagrams for these compounds. State in each case why the substituents have the positions you state. To what extent could you confirm your predictions experimentally? oH 0 0 Br H Purpose of the problem exploration of conformation and establishing the link with NMR spectra. This problem uses material from Chapter 19. If you find it too difficult, we suggest you come back to it solution when you have read that chapter. The first two molecules have no choice about their conformation but the third does. Me Br H Confirming the conformations experimentally means measuring coupling constants in the NMR we need to look at the vital protons (marked 'H' on the diagrams below) and whether they can be seen in the spectrum. Fortunately, the interesting protons are all next functional groups so they can be seen. We probably can't see the axial proton at the ring junction the first example but trans-decalins must have axial protons there, so that is not so important. 0 Me 0 Ho Br H He H H H