Chem 238 Final Exam

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CHEM 238 Winter, 2001 FINAL EXAM Name Prof. Sasaki Please circle your TA: Dirk Schweitzer , Tyan Carter, Carla McDowell 175 points TOTAL Good Luck! Note: Only answers in the box will be graded. _______________________________________________________________________ _ 1. (30) (a) Draw a stepwise mechanism for the following reaction. Use curved arrows to indicate the movement of electrons. O O H3 C H+ HO OH CH3 O H3 C O CH3 O

.

(b) Briefly explain the fact that, although hemiacetal formation between methanol and cyclohexanone is thermodynamically disfavored, addition of methanol to cyclopropane goes essentially to completion.

O CH3OH

HO OCH3

O

, cyclopropanone cyclohexanone

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2. (35) A β, γ-unsaturated carbonyl compound rearranges to a more stable conjugated α,β-unsaturated compound in the presence of either acid or base. O H+ or OHO

A !,"-unsaturated carbonyl compound

A #,!-unsaturated carbonyl compound

(a) Propose a mechanism for the base-catalyzed rearrangement.

(b) Propose a mechanism for the acid-catalyzed rearrangement.

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3. (35) Predict the structures of the products or starting materials in the following equations. Show stereochemistry when it is known. (a)

O P + CH3

(b)

H3 CO

1) BH3 :THF 2) H2 O2 , OH-

(c)
H3 C 1) Mg, THF H3 CO Br 2) D2 O

(d)
O H3 C O H N CH3 HNO3 H2 SO4

(e)

O O

O

1) NH2 -NH2 2) NaOH, heat

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4. (35) (a) Provide a reasonable synthesis for the following compounds from the indicated materials. You may use any reagents that you wish to use. (a) CH2 OH from CH2 OH CH3 CH2 O O OCH2 CH3 and compounds with 4 carbons or less O

(b)
O

from benzene and any compounds with 2 carbons or less.

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5. (35) A number of plants produce chemical substances that prevent insects from feeding on them. Some steps in the synthesis of such a compound, called an antifeedant, are shown bellow. Supply reagents for the transformations. (The wavy lines indicate either that stereochemistry is not known or that a mixture of stereoisomers may exist.) H3 C O H3 C O O

A
H3 C H3 C

B
H3 C

H3 CO

O

OH

H

C
H3 CO

O

D
H3 C H CH2 H3 C

H3 CO

O

EtO- Na+ EtOH
H3 C

H3 CO

O

O

H

O

H

E

H3 C

O

H3 C H CH2

A:

B:

C:

D:

E:

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