Chemistry 2030 Introduction to Organic Chemistry Fall Semester 2017 Dr. Rainer Glaser

Size: px

Start display at page:

Download "Chemistry 2030 Introduction to Organic Chemistry Fall Semester 2017 Dr. Rainer Glaser"

James Fowler
6 years ago
Views:

1 Chemistry 2030 Introduction to Organic Chemistry Fall Semester 2017 Dr. Rainer Glaser Examination #3 Nucleophilic Substitutions & Eliminations, Alcohols, and Ethers Thursday, November 2, 2017, 8:25-9:15 am Name: Question 1. Nucleophilic Substitution and Elimination Reactions 20 Question 2. Reactions of Organic Halides with Nucleophiles 20 Question 3. Chemistry of Alcohols 20 Question 4. Oxidation of Alcohols 20 Question 5. Chemistry of Ethers and Epoxides 20 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). 1

2 Question 1. Mechanisms of Nucleophilic Substitution and Elimination Reactions. (20 points) (a) Provide a perspective drawing of the transition state structure for the S N 2 reaction of the bromide nucleophile with 1-chloropropane. Use dashed lines for partial bonds. Draw the C---Nuc and C---L bonds horizontally in the paper plane with the leaving group on the right, and draw the C CH 2 CH 3 bond also in the paper plane and up. In this S N 2 transition state structure, the (H C H) angle is approximately (90, 109, 120 ), the (Br---C---Cl) angle is approximately (90, 109, 120, 180 ), and the (H C---Cl) angle is approximately (90, 109, 120 ). (7 points) (b) Consider the E1 reaction of (S)-3-bromo-2,3-dimethylpentane with sodium methoxide in methanol. First: Provide a perspective drawing of the substrate and pay attention to the chirality. This substrate has (1, 2, 3) types of β-hydrogens and a total of β-hydrogens. (2 points) Second: Draw the intermediate formed in the first step of the E1 reaction; the (Me C Et) angle is about (90, 109, 120 ) and the hybridization of the cationic center is (sp, sp 2, sp 3 ). (2 points) Third: Draw the structure of the major product of the E1 reaction. The major product is a (mono-, di-, tri-, tetra-) substituted alkene, the so-called (name of a chemist) product (2 points; 13 points overall) Perspective Drawing of the Substrate (3 p.) Intermediate Cation (2 p.) Major Product (2 p.) 2

3 Question 2. Reactions of Organic Halides with Nucleophiles. (20 points, 5 points each part) (a) Using complete structural formulas (all atoms, all valence electrons, formal charges, actual charges), show the substrate, the reagent, and the major product of the reaction of the sodium cyanide NaCN with 1-chloropropane. Product formed by (S N 1, S N 2). (b) Using abbreviated structural formulas, show the substrate, the reagent, and the major product of the reaction of sodium ethoxide with 3-bromo-3-ethylpentane. The nucleophile is (strong, weak). Major product formed by (S N 1, S N 2, E1, E2). (c) Using abbreviated structural formulas, show the substrate, the reagent, and the major product of the reaction of propanol with 1-bromo-1-methyl-cyclohexane. The nucleophile is (strong, weak). Major product formed by (S N 1, S N 2, E1, E2). (d) Using complete structural formulas (all atoms, all valence electrons, formal charges, actual charges), show the substrate, the reagent, and the product of the S N 2 reaction of (a huge excess of) ammonia with 1-chlorobutane. 3

4 Question 3. Chemistry of Alcohols. (20 points) (a) The boiling point of ethanol is +78.5ºC and much higher than the boiling point of -42ºC of propane. An ethanol molecule (can, can not) act as hydrogen bond donor and/or it (can, can not) act as hydrogen bond acceptor. Draw the complete Lewis structure of a reasonable aggregate formed by two molecules of ethanol. Show a hydrogen bond as a dotted line. (4 points) (b) The pk a value of H 2 O is about 16. The pk a of ethanol is about (give value). The pk a of phenol is about (give value). Hence, it (is, is not) possible to convert ethanol quantitatively to ethoxide by reaction of ethanol with NaOH, and it (is, is not) possible to convert phenol quantitatively to phenoxide by reaction of phenol with NaOH. (4 points) (c) Complete the following reaction for the formation of sodium propoxide with correct stoichiometry. Provide the stoichiometry factor even if it is one. (4 points) _ H 3 C CH 2 CH 2 OH + _ Na (d) Thionyl chloride is the dichloride of sulfurous acid. Draw complete Lewis structures of thionyl chloride and of the OS(OH) 2 isomer of sulfurous acid. (4 points) OSCl 2 OS(OH) 2 (e) Thionyl chloride is an excellent reagent to convert aliphatic alcohols to alkyl chlorides. For the reaction of (S)-2-pentanol with thionyl chloride, show the Lewis structure of the intermediate chlorosulfite ester and of the reaction product (with stereochemistry). (4 points) \ 4

5 Question 4. Oxidation of Alcohols. (20 points) (a) Provide structural formulas and the names of the products formed by oxidation of ethanol. Provide the structures of hydroquinone and its oxidation product 1,4-benzoquinone. (4 points) Aldehyde from EtOH Carboxylic Acid from EtOH Hydroquinone 1,4-Benzoquinone (b) Jones reagent is a solution of chromium trioxide (CrO 3 ) or a dichromate salt (i.e., Na 2 Cr 2 O 7 ) in dilute aqueous H 2 SO 4. The active reagents are chromic acid and dichromic acid, respectively. Draw their complete Lewis structures. (4 points) H 2 CrO 4 H 2 Cr 2 O 7 (c) 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) (d) Provide the structure of the product of Jones oxidation of 4-tert.-butylcyclohexanol. (3 points) (e) Which of the following molecules is expected to function as an antioxidant? Circle all that may serve as antioxidants. (4 points) 5

Question 5. Chemistry of Ethers and Epoides. (20 points) (a) Consider the formation of methyl phenyl ether by Williamson Ether Synthesis.

This reaction will form phenol. (yes, no) B. This reaction will form methanol. (yes, no) C. This reaction will form iodobenzene. (yes, no) D. This reaction will form methyl iodide. (yes, no) E.

This reaction involves initial formation of an oxonium ion. (yes, no) (c) Draw the complete structure of peracetic acid (a.k.a. peroxyacetic acid) and draw curved arrows to show how this reagent functions as a source of oxygen atoms.

6 Question 5. Chemistry of Ethers and Epoides. (20 points) (a) Consider the formation of methyl phenyl ether by Williamson Ether Synthesis. Show the structures of the substrate, the reagent, the product and of the inorganic product. (6 points) (b) Consider the ether cleavage of methyl phenyl ether with HI. (4 points, 0.5 points each) A. This reaction will form phenol. (yes, no) B. This reaction will form methanol. (yes, no) C. This reaction will form iodobenzene. (yes, no) D. This reaction will form methyl iodide. (yes, no) E. This reaction follows an S N 1 mechanism. (yes, no) F. This reaction follows an S N 2 mechanism. (yes, no) G. This reaction follows an E1 mechanism. (yes, no) H. This reaction involves initial formation of an oxonium ion. (yes, no) (c) Draw the complete structure of peracetic acid (a.k.a. peroxyacetic acid) and draw curved arrows to show how this reagent functions as a source of oxygen atoms. Provide a perspective drawing of the product formed by the reaction of cis-2-butene with peracetic acid in the box to the very right. (6 p.) Peracetic Acid, an O -source Cis-2-butene + Peracetic Acid (d) Consider the cleavage of 1-butene oxide with methanol. This reaction can be performed with acid-catalysis. Draw the structure of the product and pay attention to the regiochemistry. (4 points) 1-butene oxide, H 2 SO 4, and H 3 C OH 6

Chemistry 2030 Introduction to Organic Chemistry Fall Semester 2015 Dr. Rainer Glaser

Chemistry 2030 Introduction to Organic Chemistry Fall Semester 2015 Dr. Rainer Glaser Examination #3 Nucleophilic Substitutions & Eliminations, Alcohols, and Ethers Thursday, November 5, 2015, 8:25-9:15