—  1  —  

       

Chemistry  2030      “Introduction  to  Organic  Chemistry”      

Fall  Semester  2012      Dr.  Rainer  Glaser      

Examination #3

“Alcohols, Ethers, Aldehydes & Ketones.”

Posted 10/25/12 @ 8 am; Return 10/26/12 @ 1pm (DoCh Office)

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 100

—  2  —  

Question 1. Names, Bonding and Properties. (20 points) (a) Provide abbreviated structural formulas. (4 points)

Glycerol

Glycol

Propylene Oxide

THF

(b) The electrostatic potential (ESP) maps are shown for propylene oxide, glycol, and acetic acid. In row #1, provide the name of the compound whose ESP map is shown on top of the column. Find the boiling points of these compounds (in °C) and provide them in row #2. 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 pts)

#1 glycol propylene oxide acetic acid

#2 197.3 °C 34 °C 118-119 °C

#3 Donor No Donor Donor

#4 Acceptor Acceptor Acceptor

(c) Propylene oxide is soluble in water. In an aggregate formed by one propylene oxide molecule and one water molecule, propylene oxide can act as hydrogen bond _________ (acceptor, donor) and water 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)

—  3  —  

Question 2. Alcohol and Ether Chemistry. (20 points) (a) For the reaction of 1-propanol with phosphorous tribromide, show Lewis structures of the substrate, the reagent, the organic product and of the inorganic product. (4 points)

HP(O)(OH)2 is fine as well

(b) Suggest a practical synthesis of anisole (methoxybenzene) by Williamson Ether Synthesis. Show Lewis structures of the substrate, the reagent, the ether product and of the inorganic product. (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)

Radical formed by H-abstraction from Diethyl Ether

Hydroperoxide formed by Air Oxidation of Diethyl Ether

(d) Consider the acid-catalyzed cleavage of propylene oxide with 1-propanol. Provide abbreviated structural formulas for the protonated epoxide substrate and of 1-propanol, of the intermediate formed by the addition of 1-propanol to the epoxide, and of the final product. Use curved arrows to describe the mechanism. (8 points)

—  4  —  

Question 3. Oxidation of Alcohols and Aldehydes. (20 points) (a) The oxidation of primary alcohols to aldehydes is possible with the reagent PCC in ____CH2Cl2__ solution (give formula of solvent). Provide the full name of PCC and provide the names of the three compounds that are combined to form PCC. PCC is a salt; draw the structures of the cation and of the anion of this salt. (4 points)

pyridinium chlorochromate

(b) Provide abbreviated structural formulas of the substrate butane-1,3-diol and of the products of its oxidations with Jones’ reagent and with PCC. (6 points)

butane-1,3-diol

Product of Jones’ oxidation

Product of PCC oxidation

(c) Show the Lewis structures of the products of oxidation of hydroquinone (1,4-dihydroxy-benzene) and its isomer catechol (1,2-dihydroxybenzene) with Na2Cr2O7 in aq. H2SO4. Provide the names of the products of oxidation. (6 points)

Hydroquinone Oxidation

1,4-benzoquinone “benzoquinone”

Catechol Oxidation

1,2-benzoquinone

(d) Vitamin E (α-tocopherol) functions as an antioxidant. Briefly explain how Vitamin E functions as an antioxidant. (4 points)

Vitamin E contains a phenol. A reactive radical can abstract a hydrogen atom from the OH group of the phenol. The resulting radical (shown) is stabilized because it can be delocalized.

—  5  —  

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. Provide a perspective drawing of phenyl magnesium bromide solvated by two diethyl ether molecules. (4 points)

(b) Starting with 2-bromopropane, show the reaction to prepare the Grignard reagent and then show how the Grignard reagent reacts with D2O. Provide structures of the substrate, the Grignard intermediate, and of the product of hydrolysis. (6 points)

(c) What is the product expected from the reaction between methylmagnesium bromide and 2-butanone 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)

(d) Consider the reaction of cyclohexanone with sodium acetylide. Provide structures of the substrate, of the initial addition product, and of the product formed after hydrolysis. (6 points)

—  6  —  

Question 5. Acidity and Basicity. (20 points) (a) The pKa value of phenol is 10 and, hence, the Ka of phenol is __10-10_. (2 points) (b) The pKa value of ethanol is about _16_, and hence __________ (ethanol, phenol) is the stronger acid. (2 points) (c) For each pair, select the more acidic compound. (4 points)

H3C−COOH or

F3C−COOH

para-nitrophenol

or 2,4,6-trinitrophenol

(d) Complete the following equations for reactions of ethanol. (6 points)

H3C−H2C−OH + Na à H3C−H2C−O- Na+ + ½ H2

H3C−H2C−OH + NaH à H3C−H2C−O- Na+ + H2

H3C−H2C−OH + NaOH à { H3C−H2C−O- Na+ + H2O } very little, NaOH is not strong enough

(e) Draw the complete structural formula of the enol form of acetone. (2 points)

(f) Draw the complex formed between the Lewis base acetone and the Lewis acid AlCl3. (4 points)