Name___________Key_______________ 216 H W13-Exam No. 1 Page 2 I. (10 points) The goal of recrystallization is to obtain purified material with a maximized recovery. For each of the following cases, indicate as to which of the two goals, (A) maximum recovery and (B) purity, would be adversely affected by the recrystallization method indicated. Write (A) or (B) for each of the questions. (1) In the initial dissolution step, an unnecessarily large volume of solvent is used. Answer__(A)__ (2) After dissolving a solid in a solvent at high temperature, the solution is not filtered. Answer__(B)__ (3) The hot solution obtained by gravity filtration after dissolving a solid in a solvent at high temperature is cooled to room temperature using an open beaker. Answer__(B)__

(4) Crystallization is accelerated by immediately placing the flask of hot solution in an ice-water bath.

Answer__(B)__

(5) The crystals obtained after recrystallization are collected by gravity filtration. Answer__(B)__ II. (11 points) In connection with our research directed at probing the molecular mechanism of chemical carcinogenesis, we carried out a series of synthetic reactions shown below. Consider the relative Rf values of the compounds shown in the following reaction scheme when analyzed by thin-layer chromatography (TLC) on silica gel-coated plates.

O OHHO

OH

NaBH4

C2H5OH CH3OHcat. HCl

Δ

1. AgOCOCH3 I2, Δ

2. NaOCH3 CH3OH

1 2 3 4

(1) (2 points) Which one should show the lowest Rf among all of the compounds 1 through 4? Answer ____4_____ (2) (2 points) Which of compounds 1 and 2 should show a higher Rf? Answer ____1______ (3) (2 points) Which of compounds 1 and 3 should have a higher Rf? Answer ____3______ (4) (2 points) Which of compounds 2 and 3 should have a higher Rf? Answer ____3______ (5) (3 points) Compound 1 is shown to have a high Rf value (~0.8) when a mixture of 3 : 1 ethyl acetate/hexanes is used as an eluent. How would you change the solvent system in order to have a considerably lower Rf value for this compound? Answer: ___Increase the fraction of hexanes in the mixture of the two solvents, e.g., 1 : 3 ethyl acetate/hexanes

Name____________Key______________ 216 H W13-Exam No. 1 Page 3 III. (17 points plus 3 bonus points) N-Benzylaniline can be prepared by reaction of benzyl chloride and aniline in the presence of aqueous sodium bicarbonate (NaHCO3).

Cl NH2NaHCO3 N

HNaCl H2O CO2+++

benzyl chloride aniline N-benzylaniline

++

The procedure calls for 372 g of aniline, 127 g of benzyl chloride, and 105 g of sodium bicarbonate dissolved in 100 mL of water, and produces 160 g of N-benzylaniline.

Write an answer in the box provided to each of the following questions.

(1) (3 points) Calculate as to how many moles of each of the reagents are used in this procedure. Use the following atomic weights: C = 12, H = 1, N = 14, O = 16, Na = 23, Cl = 35.5

benzyl chloride: _1.00___ moles; aniline: _4.00__ moles; NaHCO3: _1.25___ moles

(2) (3 points) What is the limiting reagent?

benzyl chloride

(3) (3 points) What is the theoretical yield of N-benzylaniline? Show your work.

183 g; 1.00 moles x 183 g/mole = 183 g

(4) (2 points) What is the percentage yield of N-benzylaniline? Show your work.

_______ %;87 (160 g / 183 g) x 100 = 87%

(5) (3 points) About 260 g of aniline can be recovered from the reaction. Does this affect the calculation of theoretical yield? Explain.

The recovered amount of aniline corresponds to 2.80 moles. Since in this experiment,4 mol equiv of aniline is used relative to the limiting reagent, benzyl chloride, it doesnot affect the calculation of theoretical yield.

(6) (3 points) What volume of benzyl chloride (density 1.10 g/mL) is required for the reaction?

________________ mL115.4

(7) (3 points; bonus question) Why is it necessary to use such a large excess of aniline for the reaction? Explain.

As N-benzylaniline is more nucleophilic than the starting aniline, it can undergomultiple benzylations. By the use of a large excess of aniline, the overallreaction can be directed toward the monobenzylation of aniline.

Name__________Key_________________ 216 H W13-Exam No. 1 Page 4 IV. (15 points) On the basis of its spectroscopic information provided below, answer the following questions given and draw the structure of an unknown compound (C7H16O2; a strong IR absorption in the 3400-3250 cm-1 region) in the box below. In addition, assign all 1H and 13C peaks to the corresponding nuclei. Please note that one of the 1H peaks may be assignable to the OH hydrogen(s).

!

300 MHz 1H NMR spectrum in CDCl3 (δ ppm) Proton-decoupled 13C NMR spectrum in CDCl3 (δ ppm)

16 7 15 22integrationvalues

The letter s, t, or q on top of each peak denotes the splitting pattern, singlet, triplet, or quartet, respectively, when the spectrum is run in the proton-coupled mode.

(1) (1 points) What is (are) the unit(s) of unsaturation of this compound? ____zero______ (2) (2 points) Does this compound have an ether (R-O-R’) group? _____NO______ (3) (4 points) What is the structure of (4) (8 points) Assign all 1H and 13C chemical shifts to

the compound? (no partial) the corresponding H and C nuclei in the proposed structure.

4

8

HO

HOC

CO

OC C C

CC

H H H

HHHHHH H

H

H

H

HH

H

0.8 ppm2.8 ppm

3.55ppm

3.55ppm

1.35 ppm

1.35 ppm

41ppm

7.2ppm

22ppm68 ppm

1 pt for each chem shift assignment

Name___________Key_________________ 216 H W13-Exam No. 1 Page 5

V. (15 points) An unknown compound, C9H12O, has the following spectral properties.

IR (neat): 3400-3200 (broad and strong), 3100-2850 (many medium strength peaks); no absorption peaks in the 2800-1640 cm-1 region. 1H NMR in CDCl3: δ 1.89 (2H, quintet, J = 7.0 Hz), 1.98 (1H, s), 2.65 (2H, t, J = 7.0 Hz), 3.60 (2H, t, J = 7.0 Hz), and 7.05-7.40 ppm (multiplets, 5 Hs). 13C NMR in CDCl3: δ 32.06 (t), 34.15 (t), 61.85 (t), 125.79 (d), 128.39 (d), 128.39 (d), and 141.91 (s) ppm. The letters s, d, and t indicate splitting patterns when the spectrum is run under a proton-coupled mode.

(1) (1 points) What is (are) the unit(s) of unsaturation of this compound? _____4______ (2) (2 point) Does this compound have a benzene ring? Yes No (circle the one that applies) (3) (2 point) What does the IR spectrum tell you in terms of the presence of an O-containing functional group in this molecule? __OH (or hydroxyl) group__

(4) (4 points) What is the structure of the (5) (6 points) Draw in the box below the structure compound? (no partial) you drew in (4) and assign all non-aromatic 1H peaks

and the 13C peaks at 61.85 and 141.91 ppm to the corresponding nuclei in the proposed structure.

4

6

OH

OH

H H

H H

H H

1.89 ppm (quintet)

1.98 ppm (s)

3.60 pm (t)2.65 ppm

(t)

61.85 ppm

141.91 ppm

1 pt for each chem shift assignment

VI. (15 points) On the basis of its spectroscopic information provided below, answer the questions given on page 6 and draw the structure of an unknown compound (C6H12O2; IR a strong peak at 1743 cm-1; no peaks in the 4000-3100 cm-1 region) in the box on page 6. In addition, assign all 1H peaks to the corresponding nuclei.

!

Name__________Key_________________ 215 HH W13-Exam No. 1 Page 6 VI. (continued) 13C NMR spectrum in CDCl3

! (1) (1 points) What is (are) the unit(s) of unsaturation of this compound? _____one______ (2) (2 point) What does the IR spectral information tell you in terms of the presence of an O-containing functional group in this molecule? __carbonyl group___ (3) (2 points) What do the 13C NMR spectral data tell you in terms of the presence of an O-containing functional group in this molecule? ___ester group_____ (4) (4 points) What is the structure of the (5) (6 points) Draw in the box below the structure

compound? (no partial) you drew in (4) and assign all 1H peaks and the 13C peak at 64.38 ppm to the corresponding nuclei in the proposed structure.

4

6

O

O

H3C O CH3

OH H

HH

H H

2.0 ppm

4.0 ppm

0.9 ppm

1.35 ppm

1.6 ppm 64.38 ppm

1 pt for each chem shift assignment

Name____________Key_______________ 215 HH W13-Exam No. 1 Page 7 VII. (8 points) For each of the following reactions, draw in the box provided the structure of the expected major product.

ClO

AlCl31.

2. H3O+ work-up

4

(1)

(2)

O

OHCs2CO3CH3CH2-I

50 °C, DMF

2. H3O+ work-up

4

1.

O

O

OCH2CH3

VIII. (9 points) The 1H NMR data for H4 and H5 of diol 5 are shown below. Please note that two hydroxy H’s are not involved with 1H – 1H couplings.

δ 3.72 ppm (dd, J = 12.0 and

3.4 Hz)

δ 3.88 ppm (dd, J = 3.4 and

2.5 Hz)

5Si

O

H

H O

OCH3

O

HHOHO

H1

2345 6

H

H

Si

OCH3O

O

O

1 2

345

6

H

H

HOHO

(1) On the basis of the NMR data above, show the stereochemistry of alcohol 5 at C-4 and C-5 by writing in the boxes above right Hs and OHs (6 points).

(2) Indicate below the coupling constants for each of the following (3 points): 3J3,4 = __12.0__ Hz; 3J4,5 =__3.4__ Hz; 3J5,6 = __2.5__ Hz