Part 7: STRUCTURE DETERMINATION

Note that these types of questions are often the most difficult on the examination. This is because they are holistic in that they require a good understanding of the reactions and the concepts and the ability to apply those concepts. They can't be memorised, they require understanding and ability to apply. Hence they help discriminate those who truly understand from those who have memorised and will soon forget.

A schematic of the solution is shown below. The information from the question is given in black. Deductions directly from this information are given in red. Points that provide potential key information are shown in green which leads to the structures.

The logical thought pathway would be based on identifying G from the ozonolysis results (nomenclature) or E from the spectral data. From G, one can deduce F. From E or F give the skeleton which means there are 3 possible isomers of B only one of which undergoes hydroboration / oxidation to give an alcohol D that is achiral. D then leads to A, B to C. The fact that all are achiral and that D can be converted back to A (hence no rearrangement on A-B-D path) can help with the solve. There are, of course, other possible thought pathways or factors that can help complete the solve.

Common mistakes:

• Incorrect structure for G based on nomenclature and hence wrong structure for F from the (retro) Diels-Alder reaction.
• Drawing structures with chirality centers despite the statement that none of the compounds A-G are chiral.
• Incorrect reactions for B to C or D or E.