7) Compound D exists in solution as two equilibrating isomers. In solution, ¹H NMR

spectroscopic results indicate that TOT exists in two distinct, equilibrating

conformations (each of which is present in two enantiomeric forms): the more

predominant propeller form, and the minor 'helical' form that has one C=O group

orientated in the opposite direction from the other two. The four stereoisomers have

been separated by low temperature chiral HPLC allowing assignment of the absolute

configuration and measurement of the interconversion barrier of 80 kJ mol-¹. It is only

the chiral propeller form that is observed in the crystalline state, adopting the (-)-(M)

conformation (or the enantiomeric (+)-(P) conformation of opposite helicity.

D

a. Based on the barrier to interconversion of isomers, would you expect the ¹H

NMR to show a single set of peaks for compound D?/nb. Compound D forms clathrates with the compounds shown below. Irradiation of

the crystals in the presence of O₂ and a sensitizer affords hydroperoxide

products. However, different crystals, upon dissolving and measuring optical

rotation, give opposite results. What must be true of the clathrate in order to

obtain such results?

OMe

OMe

(+)

(-)

H

H

HO

HO

Me

OMe

Me

OMe

[a] = +120°

546

546

=-146°