1. When (R)-1-chloro-2-methylbutane is subjected to free radical chlorination, five dichloro constitutiona isomers are possible.

a) Draw them and name them with the appropriate R,S-descriptors.

b) Two of the dichlorides are optically inactive. Which ones are they? Explain why and illustrate.

2. An optically-active compound A (C₁₀H₁₆, [α]_D = +124^o) reacts with H₂ in the presence of a catalyst to provide compounds B and C. [Note: Hydrogen adds to double bonds under these conditions. Thus, ethylene is converted into ethane.] Both B and C show no optical rotation, even when the solutions are diluted, both compounds have the formula C₁₀H₂₀, and both compounds are 1,4-disubstituted cyclohexanes. Compound B has an energy difference of 3.9 kcal/mol between its two chair conformations.

a) Determine the structures of B and C. Show your reasoning.

b) What is the energy difference between the two chair conformations of C? Show work.

c) The structure of A cannot be determined from the information provided. There are eight structures?, exclusive of which enantiomer is dextrorotatory, that fit the other data. Two of them are diastereomers. Draw the structures with at least one center of the (R)-configuration.

d) A sample of A is isolated from mandarin oranges and it is found to have [α]_D = +31^o. How much of the l-enantiomer is present in the sample? Show work.

3. Enriched A has an optical purity of 20% while B has an enantiomeric excess of 50%. Both compounds are rich in the (R)-enantiomer. Compounds A and B react to form two diastereomers A_RB_R:A_SB_S and A_RB_S:A_SB_R. One diastereomer is 64% optically pure while the other one is only 33% optically pure.

a) How much of each enantiomer is present in A and B? Show work.

b) What are the percentages of each diastereomer? Show work.

c) Show how the ee of each diastereomer is obtained.

d) What is the optical purity of each diastereomer? Show work.

4. a) 1,2-Dibromoethane is optically inactive yet it has a dipole moment . Explain and illustrate.
b) meso-Tartaric acid exists in three staggered conformations, none of which has a plane of symmetry. Yet the compound is optically-inactive. Explain and illustrate.

5. Which of the compounds on the right are, in principle, capable of resolution? Explain and illustrate.

6. A mixture of enantiomers contains 1-1/2 times more of one and shows [α]_D -25.0^o. What are the rotations of the pure enantiomers? Which one is in excess?

7. On the Lighter Side: The last eleven US Presidents (33-43) are shown below in order of service in addition to their party affiliation and their handedness. [Handedness is "officially" designated as how you write. Ford throwing out the "first pitch" indicates he is a rightie and not a southpaw (leftie). By the way, no photo has been converted to its mirror image by me but I found Truman as both "enantiomers". ] Everyone of these photos has something in common. Place that something (L or R) in the last column and then separate the last two columns as diastereomers and enantiomers. If you can correlate their diastereoisomerism with party affiliation, you are better than I am.

 

President	Affiliation (D = Democrat; R = Republican)	Handedness	Chirality
Truman	D	L
Eisenhower	R	R
Kennedy	D	R
Johnson	D	R
Nixon	R	R
Ford	R	"R"
Carter	D	R
Reagan	R	R
Bush 41	R	L
Clinton	D	L
Bush 43	R	R