Download Organic Chemistry Test: CHEM 231A, Whittier College, November 2002 - Test #4 and more Exams Organic Chemistry in PDF only on Docsity!
Name: Whittier College
Organic Chemistry: CHEM 231A
Test # 4
120 Points Total November 25, 2002
- Answer the following questions: (24 points – 6 pts each)
1a. What is the shape of cyclohexane? Draw it and explain briefly why it is this shape.
1b. What is a diastereomer? Provide two structures that demonstrate what a diastereomer is. Explain briefly.
1c. What are the experimental / physical differences between diastereomers? Explain briefly.
1d. What makes a base a good base for the E2 Reaction? Explain briefly.
- Consider the following reactions. Predict one major product for each reaction and explain your rationale: (35 points – 7 points for each)
t-butanol / heat
H Br
O
2a.
2b.
2c.
2d.
2e.
CH 3 O-^ Na+
CH 2 Cl 2?
NaOCH 3 / Et 2 O
I
O (^) K DMF
Br
Br
S
O
O
O
Et 2 O
3d. One of the diastereomers reacts at a significantly faster rate than the other diastereomer. Predict which diastereomer reacts faster and explain. Use of appropriate energy diagrams and structures is strongly encouraged. (7 points)
3e. If any stereoisomer of 3-bromo-2,2,4,5-tetramethyl hexane is mixed with t-butanol and heated, only one product is formed and each stereoisomer reacts at the same rate. What is the one product (draw the structure and name it) and explain these results? Draw a mechanism(s) using an arrow-pushing formalism that helps us understand why the reaction is different than the previous example. (5 points)
- For each of the following structures, draw the two most stable conformers and state which one is the most stable. Explain very briefly. (26 pts total: 4a – 4c = 6 pts; 4d = 8 pts)
4a.
4b.
4c.
F
Br
4d. The optical rotation of enantiomerically pure (1R, 2R, 3R) 2,4-dimethyl-1- tert butylcyclohexane (compound in 5c) is +78°. A bottle of the chemical is found in the stockroom. By GC-MSD, only one peak is observed and the molecular ion peak has a mass of 168 m/z. The optical rotation of the bottle is –62°. 4d1. What is the optical purity for the substance? (2 points)
4d2. What is the major stereoisomer present (by name) and what percent of the total bottle is represented by this stereoisomer? Show your work. (6 points)
