CHEMISTRY 220a
Friday, November 9, 2001
NAME (print): ______________________________________________________________
TA:_____________________ Section Day:_________________ Section Time:__________
Take a few moments to look over the exam. Answer each question on the exam paper.
Important clues and instructions are in bold.
Do all preliminary drawing or computations on the work sheets at the end of the exam. The work sheets will not be graded. There is a Periodic Table on the last page of the exam.
The exam is 55 minutes.
STOP writing and hand in your exam when you are asked to do so.
REMEMBER: Neatness is to your advantage.
1. (20 pts) ______
2. (20 pts) ______
3. (20 pts) ______
4. (25 pts) ______
5. (15 pts) ______
__________________________
Total (100 pts)
1. (20 pts.) Compound A (C7H12) reacts with O3 followed by dimethyl sulfide reduction to provide a single compound E, which contains a ketone and aldehyde group, i.e., ketoaldehyde E. When A reacts with HBr in the presence of peroxide, two stereoisomeric bromides, B and C, are formed. Bromide B reacts with KOH to give mainly A and some D, whereas bromide C affords only compound D upon reaction with KOH. Ozonolysis of D provides dialdehyde F. What are the structures A-E? Provide a very brief conformational rationale for the assignment of structures to B and C. Place the structures in the appropriate boxes. [Hint: F is a good place to start.]
2. (20 pts.) Design a synthesis of meso [achiral and not (±)] epoxide 1 from 1-butyne and ethylene as your two sources [Note: 4 + 2 = 6] of carbon. All other reagents are available to you.
3. (20 pts.) Provide reagents and/or the structure of products in 4 of 5 of the following questions. Pay attention to stereochemistry where applicable.
4. (25 pts.) Circle the best answer(s) for each of the following questions:
a) The compounds that are deprotonated by 1-lithio-1-propyne (CH3CCLi)
NH3 ethanol ethane CH3NH2 ethylene
b) Given DHfo (pentane) = -35 kcal/mol and the DHo (hydrogenation) of 2-pentyne to n- pentane is -66 kcal/mol, what is the best estimate for the DHfo (kcal/mol) of 2- pentyne?
-31 +4 -100 +32 -4
c) The hexene with the smallest heat of combustion
d) The terms that describe the product derived from the reaction of OsO4 with (Z)-3-hexene.
oxidation 1,2-diol stereospecific achiral meso
e) The compound(s) with degree of unsaturation = 3.
C8H18OS C8H10ClN C12H19Br2N
5. (15 pts.) Provide a mechanism, curved arrow formalism, for one, and only one, of the following chemical transformations. Pay attention to stereochemistry where applicable.
a) The reaction of HBr with 1-butene in the presence of a peroxide
b) The conversion of 1-butene to n-butyl alcohol (1-butanol) via hydroboration.
c) The epoxidation of (E)-2-butene via the halohydrin route.