Chem 225b
Problem Set 8
Chapter 9
Due: Monday, April 3, 2006
Potassium cation solvated by the cyclic polyether, 18-crown-6 [18-membered ring; 6
oxygen atoms]. Each of the ethano groups is in a staggered conformation with each of the
O-C- C-O dihedral angles at ~60o [gauche]. For a dynamic version, click here. Note that the
six oxygen atoms occupy the same spatial arrangement as do the six carbon atoms in chair
cyclohexane. The discovery of the crown ethers by Charles Pedersen of DuPont earned him
a share in the 1987 Nobel Prize in Chemistry.
1. In the following problems, provide the missing information. Provide explanations for
your choices.
2. Cartoon A represents the cross-linking a disulfide bond in hair. This property gives hair
its natural curl or an artificial "permanent wave". When a solution of ammonium
thioglycolate at alkaline pH is applied to the hair, it goes straight to form a dithiol
(cartoon B) and disulfide C, which is water soluble and is rinsed away. To restore the
curl, the hair is washed with a mild oxidant. Provide a mechanism for the formation of B
and C from A, and the formation of A from B.
