Chemistry2030 “IntroductiontoOrganicChemistry...
Transcript of Chemistry2030 “IntroductiontoOrganicChemistry...
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Chemistry 2030 “Introduction to Organic Chemistry”
Fall Semester 2013 Dr. Rainer Glaser
Examination #3
“Alcohols, Ethers, Aldehydes & Ketones.”
Thursday, October 24, 2013, 8:25 - 9:15 am
Name:
Question 1. Names, Bonding and Properties 30 Question 2. Alcohol and Ether Chemistry 20 Question 3. Oxidations of Alcohols and Aldehydes 18 Question 4. Chemistry with Organometallic Compounds 20 Question 5. Acidity and Basicity 12 Crossword Extra Point Opportunity 10
Total 100 ALLOWED: Periodic System of the Elements (printed, w/o handwriting on it). Molecular models (you can bring pre-made models). Simple, non-programmable calculator (not really needed). NOT ALLOWED: Books. Notes. Electronic devices of any kind (other than a simple calculator).
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Question 1. Names, Bonding and Properties. (30 points) (a) Provide complete structural formulas showing all atoms and all lone pairs. Provide the missing systematic IUPAC names or the missing trivial names of the four compounds. (8 points)
Trivial Name: ______________ Trivial Name: glyceral
Syst. IUPAC Name: 1,2,3-propanetriol Syst. IUPAC Name: ______________________
Trivial Name: _______________ Trivial Name: propylene glycol
Syst. IUPAC Name: 1,2-ethanediol Syst. IUPAC Name: ____________________
(b) Ethanol is soluble with water in any ratio. In an aggregate formed by one ethanol molecule and one water molecule, ethanol can act as hydrogen bond acceptor or as a hydrogen bond donor. Draw the complete Lewis structures (all atoms, all lone pairs) of both aggregates. Use dotted line to indicate hydrogen bonds. (4 points)
Water Aggregate with Ethanol as HB Acceptor
Water Aggregate with Ethanol as HB Donor
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(c) Electrostatic potential (ESP) maps of nitrobenzene and aniline. (18 points) Nitrobenzene is planar and the electrostatic potential is the same on both faces of the molecules. Aniline contains a pyramidal amino group and the two faces of aniline are not the same. Row #1: Provide a perspective drawing of the compound whose ESP map is shown on top of the column. Draw the structure in the same orientation as was used to generate the ESP map. Row #2: Provide the name of the compound whose ESP map is shown on top of the column.
Row #3: Write whether the above compound is “activating “ or “deactivating” in electrophilic aromatic substitution.
Row #4: Mark whether the above ESP map contains a hydrogen bond donor region (write “Donor” or “No Donor”). In the image on top of the column, draw an arrow to point to the center of each HB donor region. Row #5: Mark whether the above ESP map contains a hydrogen bond acceptor region (write “Acceptor” or “No Acceptor”). In the image on top of the column, draw an arrow to point to the center of each HB acceptor region.
#1
#2
#3
#4
#5
(18 points total: 1 point for each cell and 3 points for drawing the arrows in the images)
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Question 2. Alcohol and Ether Chemistry. (20 points) (a) Phosphorous tribromide, PBr3, is the tribromide of H3PO3, ________________ (phosphoric, phosphorous, hypophosphorous) acid. The acid “H3PO3” occurs as two isomers and these are P(OH)3 and HPO(OH)2. The isomer P(OH)3 contains a _________ (pyramidal, trigonal planar) P-atom with three OH groups attached and ______ (no, one, two, three) lone pair(s) at P. The isomer HPO(OH)2 contains a pyramidal P-atom with two OH groups attached, one P–H bond, one P=O bond, and _____ (no, one, two, three) lone pair(s) at P. (4 points) (b) For the reaction of 1-hexanol with thionylchloride, show Lewis structures of the organic product and of the inorganic products. (4 points)
Organic Product
Inorganic Products
(c) Suggest a practical synthesis of dibenzyl ether, O(CH2–Ph)2, by Williamson Ether Synthesis. Show Lewis structures of the substrate, the reagent, the ether product and of the inorganic product. (4 points) (d) 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 Dipropyl Ether
Hydroperoxide formed by Air Oxidation of Dipropyl Ether
(e) Draw the Lewis structure of MCPBA in the box to the immediate right and provide its full name. Provide a perspective drawing of product formed by the reaction of cis-2-butene with MCPBA in the box to the very right. (4 points)
MCPBA
cis-2-butene + MCPBA
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Question 3. Oxidation of Alcohols and Aldehydes. (18 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. Draw the structures of the cation and of the anion of this salt. (5 points)
(b) An alternative to PCC is PDC, pyridinium dichromate. PDC is the pyridinium salt of dichromate and can be obtained by addition of pyridine to a solution of chromium trioxide in water. Draw the structures of the cations and of the anion of this salt. (3 points)
(c) Provide abbreviated structural formulas of the substrate butane-1,4-diol and of the products of its oxidations with Jones’ reagent and with PCC. (6 points)
butane-1,4-diol
Product of Jones’ oxidation
Product of PCC oxidation
(d) Phenol and its derivatives function as antioxidants. Briefly explain (i) how phenol reacts with hydroxyl radical and (ii) why the product of that reaction is less harmful than hydroxyl radical. (4 p.)
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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. Provide a perspective drawing of phenyl magnesium bromide solvated by two diethyl ether molecules. (4 points)
(b) What are the structure and the name of the product obtained by reaction of phenylmagnesium bromide and ethylene oxide and subsequent hydrolysis? This reaction exemplifies a rather general approach to two-carbon elongation in synthesis. (4 points)
(c) Starting with allyl bromide (H2C=CH–CH2–Br), show the reaction to prepare the Grignard reagent and then show how the Grignard reagent reacts with D2O. Provide structures of the Grignard intermediate and of the product of hydrolysis. (4 points) (d) Consider the reaction of benzaldehyde with ethylmagnesium bromide. Provide structures of the substrate, of the initial addition product, and of the product formed after hydrolysis. (4 points) (e) Consider the reaction of cyclopentanone with sodium cyanide. Provide structures of the substrate, of the initial addition product, and of the product formed after hydrolysis. (4 points)
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Question 5. Acidity and Basicity. (12 points) (a) Consider the acidities of water, alcohols, phenols, and of alkanes. (6 points: 1 point for each blank)
à The pKa value of ethanol is about 16 and, hence, the Ka of ethanol is ______.
à The pKa value of phenol is about ____.
à Ethanol is a __________ (weaker, stronger) acid compared to phenol.
à Considering the acidities of ethanol and phenol, it is clear that ethoxide is a _____________ (weaker, stronger) base compared to phenoxide.
à The pKa value of methane is about 50. Considering the acidities of methane and water, it is also clear that the carbanion in methyl magnesium bromide ________ (can, cannot) be protonated by water.
à 2,2,2-trifluoroethanol (F3C–CH2–OH) is _______ (more, less) acidic compared to 3,3,3-trifluoropropanol (F3C–CH2–CH2–OH).
(b) Complete the following equations. (6 points)
HO−CH2−CH2−OH + 2 K à
HO−CH2−CH2−OH + 2 NaH à
H3C−H2C−SH + NaOH à
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Extra Point Opportunity
Across (5 pts) 1) __________ is used to oxidize a primary alcohol to it corresponding aldehyde. 2) 2,2-‐diethoxy pentane can be synthesized via acetal formation using a carbonyl compound, 2-‐pentanone, and an appropriate alcohol, __________. 3) Provide name of (dash is not needed) 4) Common name of the smallest ketone is____________. 5) Oxidation with peroxyacid of cis-‐alkene, eg cis-‐2-‐butene, gives _____ isomer of epoxide. 6) _____________ (common name of cyclic ether) undergoes cleavage in acidic water, giving butane-‐1,4-‐ diol. 7) When mix water and acetone, hydrogen bond is formed between two molecules. Water acts as the hydrogen bond_________. 8) Epoxides (eg. ethylene oxide) are synthesized from corresponding alkenes (eg. ethylene) by using __________ (use abbreviation of an oxidizing agent). 9) Jones’ reagent cannot be used to oxidize ________ alcohol to its corresponding aldehyde, because further oxidation take place and the aldehyde is converted to its corresponding acid. 10) 1-‐phenyl propanol could be made from a Grignard reagent, ethyl magnesium bromide, and an aldehyde, ______________(common name). Down (5 pts) 1) Ethanol could be converted to ethyl chloride by using _____________ which gives HCl and SO2 gases as byproducts. 2) An ether could be made via Williamson Synthesis where an alcohol and an alkyl halide are used as starting materials. To synthesize phenyl propyl ether, one may use _________ and chloro propane. 3) Ethanol and propylene oxide can form hydrogen bond where the cyclic ether acts as a hydrogen bond ____________. 4) 1-‐phenyl propanol could be made from an aldehyde, propanal, and a Grignard reagent, R-‐MgX where R = __________. 5) Cyclohexanone is converted to 1-‐methyl cyclohexanol by using Grignard Reagent (R-‐MgBr) where R = _________. 6) trans-‐alkene undergoes epoxidation with m-‐Chloroperoxybenzoic acid to give _______-‐epoxide. 7) 2-‐hydroxy-‐1-‐phenylpropane is formed when propylene oxide undergoes ring opening where phenyl magnesium bromide ___________ at carbon number 1 of the epoxide ring. 8) The common name of the smallest aldehyde is ________________. 9) Provide common name of 10) ______________ alcohol (eg. tert-‐butyl alcohol) can’t be oxidized by neither PCC nor Jones’ reagent.
OH
O2N
OH