CHEMISTRY Section A4. MIDTERM October 22, Dr. John C. Vederas. 150 Points - 80 Minutes

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1 CEMISTRY Section A4 MIDTERM ctober 22, Dr. John C. Vederas 150 Points - 80 Minutes Part Points PRIT LAST AME: I 56 KEY II 16 ID UMBER (If Known): III 24 IV 30 SIGATURE: V 24 Total 150 Before you begin be sure that your exam has 13 consecutively numbered pages including this cover sheet. Do not begin until told to do so. When you begin, please print your name on each page of this exam in the upper right hand corner. Loose pages without names will be discarded. Illegible answers will be marked as incorrect. o books, notes, or unauthorized communications are permitted. If you have any questions or problems, please raise your hand. Do not leave your seat without permission. Models are permitted but may not be handed to another and CALCULATRS or other electronic devices are to be used. o otes or books. GD LUCK "othing is so firmly believed as that which is least known - a persuasion of certainty is a manifest testimony of foolishness." Michael Eyquem, Sieur de Montaigne "The reason why we have two ears and only one mouth is that we may hear more and talk less." Zeno of Citium (Cyprus) ca BC It must not be assumed that atoms of every sort can be linked in every variety of combination. -from n the ature of the Universe by Titus Lucretius Carus ( BC)

2 2 AME KEY I. Structure and omenclature - 54 Points A. Draw structures for which names are given, or name the given structures by any correct (systematic or common) nomenclature. Be sure to give cis or trans (Z or E), or if appropriate R or S, assignment to the isomer where indicated by asterisks (***). (4 points each) 1. dibenzyl ether 2. glycerol 3. ethylene glycol 4. 4-hydroxy-3-methoxybenzaldehyde (Available in Safeway as a food additive) C *** 5. C 3 (a C16 compound) (a pheromone which induces interspecies mating of male cotton bollworms with female tobacco budworms thereby killing both) cis-11-hexadecen-1-ol (or Z-11-hexadecen-1-ol) *** 6. (perfume constituent from apples) trans,trans (or E,E)-3,7,11 trimethyl-1,3,6,10-dodecatetraene

3 3 AME KEY 7. para-hydroxyaniline (a photographic developer) 2 8. (R)-trans-2-phenyl-3-octene (use part structure below in your drawing to assist grading) B. Determine whether the following pairs of structures are identical, structural isomers, diastereomers or enantiomers. (4 points each) 1. and 2. Enantiomers and Enantiomers 3. 2 and 2 Identical 4. C C and C C Diastereomers

4 4 AME KEY C. Zoroastrians utilized the common hemp plant, Cannabis sativa (marijuana), as a mind-altering drug more than 2500 years ago. owever the most common use of the plant was to make rope, and it was first imported to Canada in The major active compound in cannabis is Δ 1 -tetrahydrocannabinol (Δ 1 -TC) whose structure is shown below. Examine its structure and answer the questions which follow. Be sure to write your answer clearly inside the boxes where provided. (8 points total - 1 points each) chiral center 1. The number of carbons in Δ 1 -tetrahydrocannabinol (Δ 1 -TC) is: 21 1 point each 2. The number of hydrogens in Δ 1 -tetrahydrocannabinol is: The number of stereogenic centers in Δ 1 -tetrahydrocannabinol is: 2 4. The stereochemistry of the indicated chiral center in Δ 1 -TC is: R 5. The total number of possible stereoisomers of Δ 1 -tetrahydrocannabinol is (include Δ 1 -tetrahydrocannabinol in the number) 4 6. Draw an arrow (---->) to the most acidic hydrogen in the above structure of Δ 1 -TC 7. The approximate pka of this most acidic hydrogen in Δ 1 -TC is about: (round off to integral value) 8. The experimental pka of water is about (round off to integral value) 10 16

5 5 AME KEY II. Physical Properties and Reactivity - 16 points A. In the group below circle all compounds that have a pka below (less than) that of water. 2 pts C 3 C 2 C 3 C 2 C 2 C 3 C 3 C B. ne of the two species below is aromatic and the other is not. Circle the aromatic one. Then give the number of π electrons that both of them have and list the key criteria that make a molecule or ion aromatic. (4 pts this question: 1 pt for correct circle, 1 pts correct number electron, 2 pts for requirements for aromaticity below ) 8 π electrons Key Requirements for Aromaticity are: (2 pts) 6 π electrons cyclic planar fully conjugated 4n+2 π electrons

6 6 AME KEY C. In the group below use an arrow to indicate position(s) on the aromatic ring which would be most likely to be attacked by bromine in the presence of AlBr 3 (4 pts - 1 pt each) Example: C 3 Br C 3 SC 3 S 3 3 C K, but hindered D. Circle the most acidic of the two alcohols shown below. Draw the extra resonance structure of the corresponding anion to show what makes your choice especially acidic. (6 pts: 1 pt for correct circle) 2 2 2

7 AME KEY III. Definitions and Applications - 24 Points A. Define each of the following terms in 10 words or less (no example necessary) 2 points each 16 pts 1. tautomers rapidly interconverting structural isomers 7 2. LUM lowest unoccupied molecular orbitals 3. diasteromer a stereoisomer of a compound that is not an enantiomer 4. concerted reaction process in which all bonds form and break at same time 5. inductive effect donation or withdrawal of negative charge through single bonds 6. Lewis acid a substance that accepts a pair of electrons 7. steric effect a repulsive non-bonded interaction between atoms with inert gas configuration 8. resonance forms depictions of same molecule made by moving electrons without change of atom positions

8 C 2 C2 n Rubber (1) AME KEY _ 8 B. The compounds shown below were discussed in class. Identify them by common name and briefly (10 words or less) describe their importance or use. (8 points total - 2 pts each) 1. 3 C Tires (or similar application) (1) 2. 3 C Quinine (1) Antimalarial (1) 3 4. β-carotene (1) occurs in all plants (eg orange of carrots) DDT (1) Insecticide or Environmental Contaminant (1)

9 AME KEY IV. Reactions - 30 Points 9 A. Show the structure of the major organic product of each of the following reactions. Show stereochemistry where indicated by asterisks (***). (3 points each - 15 points total) 1. KMn 4 (hot 2 ) 2 C C 2 2. F Al 3 F and/or ortho isomer *** 3. eat 4. Al C 3 heat C 3

10 10 AME KEY B. Show reagents that will do the required transformations. In some cases two steps may be necessary. 1. Zn / (g optional) (3 pts each - 15 pts total) 2. C 3 C 2 or other acid C 2 C , 2 S , Al 3 or other Lewis acid , Fe 3 2. C 3 C Al 3 or other Lewis acid 5. 2 S 4 2 or other acid

11 AME KEY V. Synthesis and Mechanism - 24 Points 11 A. The common fabric dye avy Blue can be synthesized from benzene, naphthalene and the naphthalene derivative shown in several steps. Provide the missing reagents and intermediates to show how to complete the synthesis of avy Blue. (11 points). 3 S S 3 avy Blue From S 3 2 S 4 S 3 3 S 2 S S 4 3 Combine Final Product 3 S Sn 2 Sn 2 3 S 3 S 2 a 2 a 2 3 S 3 S 2

12 AME KEY 12 B. Versalide has a strong musk odor and is commercially synthesized for use in perfumes. utline a short synthesis of versalide from benzene, inorganic reagents. Several steps will be required. (6 points ) 2,5-dichloro-2,5-dimethylhexane, and any other necessary organic or from and Al 3 Al 3 Al 3

13 13 AME KEY C. The first steps of a mechanism for the acid-catalyzed polymerization of butadiene are shown below, but it is missing curved arrows to indicate the movement of electrons as well as charges. Complete the mechanism by putting in the correct arrows and charges. Check carefully each one is worth points. (7 Points Total) verall Reaction: 2 C C C C2 2 S Mechanism: ( add missing charges and curved arrows ) S 4 S 4 S 4 C C C C2 2 S 4 S 4