Chemistry 2050 Introduction to Organic Chemistry Fall Semester 2011 Dr. Rainer Glaser

Transcription

1 Chemistry 2050 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: 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 1

2 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, C, and 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 #2 #3 #4 (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) 2

3 Question 2. Alcohol and Ether Chemistry. (20 points) (a) Phosphorous tribromide, PBr 3, is the tribromide of phosphorous acid, H 3 PO 3. Draw complete Lewis structures of phosphorous tribromide and of two isomers of phosphorous acid. (6 points) PBr 3 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 O 2 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) 3

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 solution (give formula of solvent). Provide the full name of PCC. (4 points) (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 Na 2 Cr 2 O 7 in aq. H 2 SO 4 affords 1,4-benzoquinone. Its isomer catechol (1,2-dihydroxybenzene) undergoes a similar oxidation with Na 2 Cr 2 O 7 in aq. H 2 SO 4. 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) 4

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. 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 D 2 O. (6 points) (c) What is the product expected from the reaction between ethylmagnesium bromide and 3- pentanone 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) The alcohol C 6 H 5 CH(OH) CH 3 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) 5

6 Question 5. Acidity and Basicity. (20 points) (a) The Ka value of ethanol is and, hence, the pka of ethanol is. (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 OH + NaH (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) 6