Chemistry
205 0 “Introduction
to
Organic
Chemistry”
Fall
Semester
2011
Dr.
Rainer
Glaser
Examination #3
“Alcohols, Ethers, Aldehydes & Ketones.”
Wednesday, October 26, 2011, 10 – 10:50 am
Name:
Answer Key
Question 1. Names, Bonding and Properties
20
Question 2. Alcohol and Ether Chemistry
20
Question 3. Oxidations of Alcohols and Aldehydes
20
Question 4. Chemistry with Organometallic Compounds
20
Question 5. Acidity and Basicity
20
Total
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1
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100
Question 1. Names, Bonding and Properties. (20 points)
(a) Provide abbreviated structural formulas. (4 points)
Glycerol
Propylene Oxide
(b) The electrostatic potential (ESP) maps are shown for ethanol, dimethyl ether, and acetaldehyde.
In row #1, provide the name of the compound whose ESP map is shown on top of the column. In row
#2, provide the boiling points of these three compounds; the values are -24 °C, +20.2 °C, and +78.5 °C.
In row #3, mark whether the above compound is a hydrogen bond donor (write “Donor” or “No
Donor”). In row #4, mark whether the above compound is a hydrogen bond acceptor (write “Acceptor”
or “No Acceptor”). (12 points)
#1
Dimethyl ether
Acetaldehyde
Ethanol
#2
-24 °C
+20.2 °C
+78.5 °C
#3
No Donor
No Donor
Donor
#4
Acceptor
Acceptor
Acceptor
(c) Acetone is soluble in ethanol. In an
aggregate formed by one acetone and one
ethanol molecule, acetone can act as hydrogen
bond _________ (acceptor, donor) and ethanol
will act as hydrogen bond _________ (acceptor,
donor). Draw the complete Lewis structure of
this aggregate. Use a dotted line to indicate the
hydrogen bond. (4 points)
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2
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Question 2. Alcohol and Ether Chemistry. (20 points)
(a) Phosphorous tribromide, PBr3, is the tribromide of phosphorous acid, H3PO3. Draw complete Lewis
structures of phosphorous tribromide and of two isomers of phosphorous acid. (6 points)
PBr3
P(OH)3
HPO(OH)2
(b) Phosphorous tribromide is an excellent reagent to convert alcohols to alkyl bromides. For the
reaction of 2-propanol with phosphorous tribromide, show Lewis structures of the substrate and the
organic products (no need to provide the inorganic products). (4 points)
(c) Ethers are prone to oxidation by
air by way of radical reactions.
The O2 molecules in air are
diradicals and they can initiate
radical chemistry by H-abstraction
from a C-atom directly connected
to the ether-O. Provide the Lewis
structures requested. (4 points)
Hydroperoxide formed by Air Oxidation of Diethyl Ether
(d) Provide abbreviated structural formulas for the substrates and the product of the acid-catalyzed
ether cleavage of ethylene oxide by glycol. (6 points)
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3
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Question 3. Oxidation of Alcohols and Aldehydes. (20 points)
(a) The oxidation of primary alcohols
aldehydes is possible with the reagent PCC
___CH2Cl2___ solution (give formula
solvent). Provide the full name of PCC.
points)
to
in
of
(4
Pyridinium chlorochromate
(b) Provide abbreviated structural formulas of the substrate 1,6-hexandiol and of the products of its
oxidations with Jones’ reagent and with PCC. (6 points)
1,6-hexandiol
Product of Jones’ oxidation
Product of PCC oxidation
(c) Oxidation of hydroquinone
(1,4-dihydroxybenzene)
with
Na2Cr2O7 in aq. H2SO4 affords
1,4-benzoquinone.
Its isomer
catechol (1,2-dihydroxybenzene)
undergoes a similar oxidation
with Na2Cr2O7 in aq. H2SO4.
Draw the complete Lewis
structures of both oxidation
products. (6 points)
Hydroquinone Oxidation
Catechol Oxidation
(d) Butylated hydroxyanisole BHA is used as an antioxidant in foods. Briefly explain how BHA
functions as an antioxidant. (4 points)
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4
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Question 4. Chemistry of Organometallic Compounds. (20 points)
(a) Grignard reagents are made in very dry ether
solvent. The ether solvent is important to stabilize
the Grignard compound. Ether acts as a Lewis
________ (acid, base) when it complexes the
magnesium ion of the Grignard reagent. The same is
true for organolithium compounds.
Provide a
perspective drawing of phenyl lithium solvated by
three dimethyl ether molecules. (4 points)
(b) Complete the following reaction equation by providing abbreviated Lewis structures of the two
intermediates and of the final product formed after workup with D2O. (6 points)
(c) What is the product expected from the reaction
between ethylmagnesium bromide and 3pentanone followed by hydrolysis. This reaction
exemplifies the general approach for the synthesis of
a ______________ (primary, secondary, tertiary)
alcohol by reaction of a _______________ (aldehyde,
ketone) with a Grignard reagent and subsequent
hydrolysis. (4 points)
(H5C2)3COH
(d) The alcohol C6H5−CH(OH)−CH3 can be synthesized by reaction of a Grignard reagent with a
carbonyl compound and there are two options. In the boxes below, provide the Grignard reagent and the
carbonyl compound for the two synthetic options. (6 points)
C6H5MgBr and CH3CHO
C6H5CHO and CH3MgBr
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5
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Question 5. Acidity and Basicity. (20 points)
(a) The Ka value of ethanol is 1.0⋅10-16 and, hence, the pKa of ethanol is __16__. (2 points)
(b) The pKa values of HCN and phenol are 9.2 and 10.0, respectively, and hence ___________ (HCN,
phenol) is the stronger acid. (2 points)
(c) For each pair, select the more acidic compound. (4 points)
H3C−CH2−OH
or
H3C−COOH
phenol
or
para-nitrophenol
(d) Complete the following equations for reactions of phenol. (6 points)
H5C6−OH + NaOH  H5C6−O- Na+ + H2O
H5C6−OH + NaH  H5C6−O- Na+ + H2
(e) Draw the complete structural formula of the
enol form of cyclohexanone. (2 points)
(f) Draw the complex formed between the Lewis
base acetone and the Lewis acid AlCl3. (4 points)
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6
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