chemistry 51 - city university of new...

Brooklyn College, CUNY Chem. 51 NAME______________________ Recitation Instructor____________________

Chemistry 51 Spring 2008 Final Exam

1. This is a two hour and fifteen minute, closed book exam. All answers are to be put on the

question sheets. 2. Use the backsides of these pages for scratch paper. None other permitted. 3. At the end of the exam pass in all exam material. 4. There are 18 questions. Make sure you have all of them. All questions are worth 6 points. 5. Write your name on all pages of this exam. Do it now! What are the products or missing reactants of the following reactions? Indicate stereochemistry and make use of templates where provided. 1.

O

H2, NiCN -

O

H2, Ni

2

Ph

Ph

O

Ph

Ph

H2SO4, heat

product having nmr shown below

012345678PPM

5

1


3.

C(CH3)3

cold, dilute KMnO4 HIO4

4. A free radical chlorination of phenyl ethane was performed and products isolated as shown below. Using the yields shown calculate the reactivity of a benzylic hydrogen relative to a methyl hydrogen

Cl2

light

Cl

Cl

+

1.0 grams 4.0 grams. 5.

excess H2, catalyst

all unique products


6 For 2,3,4 trichloropentane how many pairs of enantiomers and how many meso structures are there?

Pairs of enantiomers

Meso structures

7. Methyl acetate can be protonated at two sites, A and B. Present a cogent argument for which site is the preferred site for protonation

O

O

A

B

Brook

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9. Present a detailed argument for which of the following two isomers, A or B, will undergo E2 reaction faster? Some templates are provided for your convenience if you care to use them.

C(CH3)3 C(CH3)3

A B

Br Br


10. Consider cis and trans decalin. Calculate the expected energy difference between the two isomers.

trans cis

11. Given the splitting constant, J = 10 Hz, of the substituted cyclohexane below complete the template to show the stereochemistry of the compound. Explain your answer.

H

H

Cl

C(CH3)3

H3C

H3CCH3

doublet with J = 10 Hz


12. How could you distinguish between the following isomers of C4H8O by mass

spectrometry

O

O

OH

A B C

=============================================================== Provide a synthesis of the following compounds. Use only ethyne as the source of all carbon atoms in the target molecules. In later problems you may also use as starting material target molecules of earlier problems even if you were not able to solve the earlier problem. Do not repeat synthetic work. You may reference a compound prepared in an earlier problem by a symbol such as 14A referring to compound A in Problem 14. 13 acetic acid, CH3CO2H 14 ethyl acetate

15. oxirane,

O


16.

OH

but-3-yn-1-ol 17.

OH

OH

hex-3-yne-1,6-diol ============================================================ 18 Give the mechanism for the following reaction. Show all important resonance

structures. Clearly indicate the expected stereochemistry of the products. Use curved arrow notation.

Ph

Cl2, H2O

chlorohydrins

Brook

klyn Collegee, CUNY

Chem Rec

m. 51 citation Ins

NAME___structor___

___________________

____________________

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Brook

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Chem Rec

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NAME___structor___

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chemistry 51 - city university of new...

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