FINAL EXAMINATION

Organic Chemistry, Chem 220a

9 A.M.; Saturday, December 12, 2009

 

 

NAME (print): ______________________________________________________________

 

TA:_____________________    Section Day:_____________ Section Time:______________

 

 

Take a few moments to look over the exam.  Do problems first with which you are most comfortable.    Important points and unknowns are in bold type.    Do all preliminary work on the worksheets.  The worksheets will not be graded.  The exam is the length of two hour exams with an additional one hour for review.  STOP writing when you are asked to do so.  Put your name on the cover sheet and subsequent pages (except for Work Sheets) where indicated.  There is a Periodic Table on page 15.

 

.Remember: Neatness is to your advantage. 

 

Have a GREAT winter break!

 

 

1.   Spectroscopy/Structure I (30 pts)              ________ 

                                                                                

2.   Reactions I (30 pts; 5 of 6)                        ________ 

                                                                                

3.   Potpourri   (48 pts; 8 of 10)                      ________             

 

4.   Structure II  (30 pts.)                                 ________

 

5.   Synthesis  ( 30 pts.)                                  ________

 

6.  Reactions II (30 pts.; 5 of 6)                      ________

 

7.  The Standard State/Structure (30 pts.)        ________

 

8.  Concepts (22 pts.; 1 of 3)                           ________                    

 

      ______________________________________________

 

Total   (250 pts)                                                                                                        


1.  Spectroscopy/Structure I:  (30 pts.) Compound A (M+ = 86), whose infrared spectrum is shown (Fig. 1, pg. 3), reacts with one equivalent of Grignard reagent B (RMgBr) to form compound C (IR: Fig. 2, pg. 3), whose mass spectrum displays a molecular ion at M+ = 102.  Compound C reacts readily with catalytic H2SO4 to give three isomers (D, E and F), two of which are stereoisomers.  Compounds D and E both form two products upon ozonolysis and dimethyl sulfide reduction, namely, G (C4H8O) and H (C2H4O).  Compound

G is inert to aqueous chromic acid.  Compound D liberates less heat upon combustion than does E. Vigorous permanganate oxidation of F forms A and CO2.  What are the structures of A – H?  Show your reasoning.

 

 

 

Fig. 1

 

Fig. 2

                                                                                   


2.  Reactions I: (5 x 6 pts. = 30 pts.)  Do 5 of 6. Provide structures for the unknown compounds. Be explicit about stereochemistry, optical activity, racemates, etc. No mechanisms required! If you do more than five problems, cross out (with a large X through the solution) the one that you do not want graded.  

 

 

 

 

 

 

 

Écontinued

 


3.  Potpourri: (8 x 6 pts. = 48 pts.) Do 8 of 10 problems. If you do more than eight problems, cross out (with a large X through the solution) the ones that you do not want graded.  

 

 

a) Circle the reagent(s) that will efficiently convert 3-hexene into propionaldehyde.

 

cat. OsO4/H2O2        HIO4       OsO4/cat. HIO4     cat. OsO4/ HIO4      O3/(CH3)2S

 

 

b)  Given the DHfo of CO2 (-94.05 kcal/mol), H2O (-68.3 kcal/mol) and acetylene (+54.5 kcal/mol), determine the heat of combustion of acetylene (C2H2).  Show work.

 

 

 

 

 

 

 

 

 

 

c) Provide a sketch of the molecular ion(s) in the mass spectrum of  1,2,3-tribromobutane.  Include the masses and intensities of the peaks. Show work.

 

 

 

 

 

 

 

 

 

 

d)  The heat of combustion of n-octane is  –1308 kcal/mol.  Predict the heat of combustion of n-decane.  Show work.

 

 

 

 

 

e)  Circle the functional group that has the lowest energy carbonyl frequency (cm-1) in its infrared spectrum.

 

RCOCl          RCO2R             RCHO                R2CO              RCONH2

 

 

f)  Cholesterol contains 27 carbons, a secondary alcohol, a double bond and four rings.  What is its molecular formula?  Show work.

 

 

 

 

 

 

 

g)  A solution of a 2:1 mixture of meso- and (R, R)-tartaric acid ([a]D = +12o) will display what specific rotation? Show work.

 

 

 

 

 

 

 

h)

New York Times, Science Times, 10/19/09 

 

      How Tongues Taste the Carbonation in a Fizzy Beverage

 

By HENRY FOUNTAIN

Published: October 19, 2009

         ÒAside from the natural and artificial flavors and sweeteners, soda and other fizzy beverages have a distinct carbonated taste. It is difficult to describe, but you know it is there when tiny bubbles of carbon dioxide go crazy all over your tongue.Ó

 

WhatÕs wrong with this picture?  What can you tell the author and graphic artist about CO2 to improve the presentation?

          

 

 

 

 

 

 

 

 

 

continued É

i) Circle the greatest number of structures that are at the same oxidation level.

 

 

 

 

 

j)  The compound C17H26Br2ClN3O3S absorbs four equivalents of hydrogen.  How many rings are present in the compound?  Show work.
4.  Structure II:  (30 pts.) Optically active ester A, C10H20O2, reacts with excess Grignard reagent B (RMgBr) to form (R)-C (C9H20O) and (S)-D (C5H12O).  Compound C is inert to PCC oxidation but D forms E (C5H10O) with this reagent.  Exposure of compound C to catalytic H2SO4 readily leads to optically inactive F (C9H18), the major E1 product.  Reduction of A with LiAlH4 affords (±)-D.  What are the structures of A-F?  Explain and illustrate.

 

 

 

 

 

 

5.  Synthesis: (30 pts.) A chemist wishes to synthesize 3-undecanone specifically labeled with deuterium at C6 to study the fragmentation pattern of alkyl ketones in the mass spectrometer.  She has at her disposal 1-hexanol, ethylene, and 1-propanol as sources of carbon to become incorporated into 3-undecanone.  She also has available D2O and LiAlD4 as deuterium sources and all other necessary reagents.  She designs a synthesis of 3-undecanone-d2.  What is her strategy?

 

 

 

 

 

 

 

 

 

 

 

6) Reactions II: (5 x 6 pts. = 30 pts.) Do 5 of 6. Provide reagents for the chemical transformations.  Several steps may be required. Additional sources of carbon may be required. If you do more than five problems, cross out (with a large X through the solution) the one that you do not want graded.  

 

 

 

 

 

 

Écontinued

7.  Standard State/Structure:  (30 pts.) Three achiral and non-racemic isomers A, B and C, two of which (A and B) are stereoisomers, all give the same alkane D (M+ = 86) upon the uptake of one equivalent of hydrogen.  The absolute difference in the heat of combustion of A and B is 0.6 kcal/mol (not 1.0 kcal/mol, which will eliminate two possible carbon skeletons) with A liberating more heat than B upon hydrogenation.  The acid-catalyzed isomerization of C to B liberates -2.0 kcal/mol of heat.  The heats of formation of C and D are

-13.4 kcal/mol and -41.0 kcal/mol, respectively:  a) Draw a Standard State diagram that employs the data given and shows the structures of A-D.  b) Determine the heats of formation of A and B. c) What are the heats of hydrogenation of A and B? Show work. [Hint: What are the possible carbon skeletons for D?  Which one, working backwards, can only be derived from A, B and C given the information provided?]

8.  Concepts: (22 pts.)  Do 1 of 3.  If you do more than one problem, cross out (with a large X through the solution) the ones that you do not want graded.

 

a) Explain and illustrate an example of the role that isotopic labeling plays in establishing the mechanism of a chemical reaction we have studied.

 

b) Using energy diagrams and commentary, distinguish between a kinetic (E2) and a thermodynamically (E1) controlled reaction.  Be sure to indicate which energy differences are relevant.  Use an example of your choosing.

 

c) Explain and illustrate an example of a stereospecific reaction.  How does it differ from one that is stereoselective?


Work Sheets

Work Sheets

Work Sheets

Work Sheets