—  1  —  

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).

—  2  —  

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

—  3  —  

(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)

—  4  —  

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

—  5  —  

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.)

—  6  —  

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)

—  7  —  

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

—  8  —  

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