216 F09-Exam #2 Page 2. Name _____Key______________

I. (6 points) There are two types of filtration methods used in organic experiments. These are: (i) gravity filtration using a short-stemmed (glass filter) funnel and fluted filter paper and (ii) vacuum (or suction) filtration using, e.g., a Hirsch funnel and round filter paper to cover the inside bottom of the funnel. For each of the following experimental operations, suggest which of the two filtration methods should be used.

(1) A step to remove insoluble impurities from a solution of a compound in hot solvent in the process of recrystallization of the compound: ___gravity filtration__________________

(2) A step to collect crystals obtained by cooling down the filtered hot solution (see above) of a compound to room temperature: ___suction filtration__________________

(3) A step to collect precipitates formed upon addition of aqueous HCl to the solution of the sodium salt of dilantin (Experiment 6): ___suction filtration__________________

II. (9 points) In a number of experiments you performed in the lab, the product mixtures were extracted with diethyl ether a few times. The combined organic layers were first washed with water and then with brine. The resulting organic solution then was dried over a drying agent such as anhydrous CaCl2, Na2SO4, and MgSO4. Answer in the boxes provided the following questions.

(1) (3 points) What is brine?

saturated aqueous NaCl solution

(2) (3 points) What is the purpose of this washing with brine?

To reduce the amount of water dissolved in (diethyl) ether.

(3) (3 points) Explain the chemical basis for the use of a drying agent? Use MgSO4 as an example. Be specific if any chemical process is involved.

MgSO4 + 7 H2O MgSO4 7H2O

III. (5 points) Ethyl alcohol [CH3CH2OH] quite often is present in technical-grade diethyl ether. If this grade of diethyl ether were used, what effect, if any, would the ethyl alcohol have on a Grignard reagent produced? Explain in the box below using words and a chemical equation with phenylmagnesium bromide [C6H5MgBr] as an example. You need not show the mechanism for this process.

MgBr+ H-O-CH2CH3 + BrMg-O-CH2CH3

is a strong base (the pK a of its conjugate acid is around 40) and it deprotonatesan acidic hydrogen of the HO of ethanol.

216 F09-Exam #2 Page 3. Name______ Key _______________

IV. (16 points) For each of the reactions given below, complete the reaction scheme by drawing in each of the boxes the structure of the expected product. Note: Ph = C6H5

CH3

OCH2CH3Ph3P

O

+ +

3

2

O

ONH

O

H

O

Ph40 °CTHF

(solvent)

H

O

H

OCH3Ph3P

O

+ +

phosphorus-containingproduct

3 2

phosphorus-containingproduct

CH2Cl2(solvent)

(1)

(2)

+

4

(3)MgBr

O

O

(2 mol equiv)

1.

diethyl ether (solvent)

2. H3O+ work-up

2C6H6O

P OPhPhPh

P OPhPhPh

OCH3

O

O

ONH

H

O

PhCH3

OCH3O

HO

HO

Ono point for

V. (6 points) Provide in the box below the structure of the necessary reagent to achieve the following transformation shown, by the use of a Wittig reaction.

H

O

O

O

O

O

+

H

O+

3

3

(1)

(2)

Ph3P O

O

O

OPh3P

Ph3P H

OPh3P O

O1. 2.acceptable:

216 F09-Exam #2 Page 4. Name_________ Key ____________ VI. (10 points) Treatment of diketone 1 with CH3ONa in methanol produced a rearranged product. The IR of the rearranged product indicates the presence of a hydroxyl group and an ester group. Draw in the box below the structure of this rearranged hydroxy ester product. You do not need to show the stereochemistry of the product.

O NN

OO

14

CH3OH (solvent)reflux, 6 h

CH3ONa O NN

HOO OCH3

or O here

Provide in the box below a reasonable step-by-step mechanism that accounts for the formation of this product. Mechanism (use an abbreviated structue of 1 as shown in the box):

O NN

OO

1OCH3

Na

6

CH3OH

O NN

O

OOCH3

O NN

OOCH3O

O NN

HOOCH3O

HOCH3

An alternative mechanism that starts with the addition of OCH3to the other C=O carbon is acceptable.

1 pt for arrows 2 pts for arrows2 pts for the structure

1 pt for the structure

2 pts for the structure

VII. (8 points) Show how many peaks you would expect to observe in the proton-decoupled 13C NMR spectra of each of the following compounds. Indicate your answers in the box provided. Do not count the 13C NMR peaks of the solvent and TMS.

H3CO

NH3O

CH3

O

O N CH3

O

H3C

H3C

CH3H3C(1) (2) (3) (4)

(room temperature)

66 6 6

chiral center!

216 F09-Exam #2 Page 5. Name _____ Key _______________ VIII. (20 points) Fill in the boxes in the following statement.

In the proton NMR spectrum of ethyl bromide [CH3CH2Br], the chemical shifts of the methyl hydrogens

and the methylene hydrogens are δ = 1.72 and 3.25 ppm, respectively, and the coupling constants

between these groups of hydrogens are 7 Hz. The number of peaks given by the methyl hydrogens is

. These methyl hydrogen peaks are separated from each other by Hz and their peak area

ratio, from the most down field peak to the most upfield peak is . The number of peaks given by the methylene hydrogens is . These methylene hydrogen peaks are separated from each

other by Hz and their approximate area ratio from the most down field peak to the most upfield

peak is . The total area of the methyl hydrogen peaks compared with that of the

methylene hydrogen peaks is in the ratio of . Of these two groups of peaks, the

hydrogen peaks are farther downfield. The chemical shift difference between these

groups of peaks of 1.53 ppm corresponds to -Hz difference on a 200 MHz instrument and

to -Hz difference on a 400 MHz instrument.

3 7

1 : 2 : 1

4

7

1 : 3 : 3 : 1

3 : 2

methylene

306

612

IX. (14 points) Consider the chemical equivalency of the hydrogen atoms in the following compounds. (1) Identify the indicated pairs of hydrogens as (H) homotopic, (E) enantiotopic, or (D) diastereotopic Hs. Write the answers as (H), (E), or (D). (2) How many unique (or discrete) hydrogens are there in each of the two compounds? Write the number of unique (or discrete) hydrogens present in each of the following two compounds.

OH

H

Ha

Hc

H

H

Hd

HbH

H

OCH3

OCH3

Ha

Hc

H

H

Hd

HbH

H

Ha and Hc _______

Ha and Hb _______

Ha and Hd _______

Ha and Hb _______

Ha and Hc _______

Ha and Hd _______

Hc and Hd _______

Hb and Hc _______

Hb and Hd _______

Number of unique (or discrete) hydrogens: ________

Number of unique (or discrete) hydrogens:

(a)

(b)3

6

(2 points)

(3 points)_________6

3E

E

H

D

DD

D

E

E

216 F09 Exam #2 Page 6. Name________ Key ____________ X. (11 points) Shown below is the 1H NMR spectrum (at 300 MHz in CDCl3) of a compound whose molecular formula is C5H12O. The IR spectrum of the compound (liquid film) shows a strong peak in the 3400-3300 cm-1 region.

(1) (1 point) What is (are) the unit(s) of unsaturation of this compound? _______zero_______

(2) (2 points) What does the IR spectral information tell you in terms of the presence of an O-containing functional group in this compound? __hydroxyl group___ (3) (8 points) Draw in the box below the structure of this compound and assign the NMR peaks (by reading their chemical shifts) to the corresponding H(s).

HO CH3

CH3

H

HH

HH

0.9 ppm

1.7 ppm

1.45 ppm

3.7 ppm

1.3 ppm

Chemical shift assignments: 1 pt eachStructure: 3 points

216 F09 Exam #2 Page 7. Name _______ Key ____________ XI. (15 ponts) On the basis of its spectroscopic information provided below, answer the questions given on page 8 and draw the structure of the compound (C6H12O2) in the box on page 8. In addition, assign all 1H peaks to the corresponding nuclei. IR spectrum (liquid film)

216 F09 Exam #2 Page 8. Name _______ Key _____________ XI. (continued)

13C NMR spectrum in CDCl3 (proton-decoupled spectrum)

(1) (1 points) What is (are) the unit(s) of unsaturation of this compound? ____one______ (2) (2 points) What does the IR spectrum tell you in terms of the presence of an O-containing functional group in this molecule? __carbonyl group__ (3) (2 points) What does the 13C NMR spectrum tell you in terms of the presence of an O-containing functional group in this molecule? __ester group_____ (4) (5 points) What is the structure of this compound? (no partial)

5

O

O

(5) (5 points) Assign all 1H shifts to the corresponding H atoms in the proposed structure.

5

H3C O CH3

OH H

HH

H H

2.0 ppm

4.0 ppm

0.9 ppm

1.35 ppm

1.6 ppm Chemical shift assignments: 1 pt each