216 S10-Exam #1 Page 2. Name

Size: px

Start display at page:

Download "216 S10-Exam #1 Page 2. Name"

Godwin Montgomery
5 years ago
Views:

2 216 S10-Exam #1 Page 2. Name I. (3 points) Arrange the following four compounds in order of their R f values when analyzed by thinlayer chromatography (TLC) on silica gel-coated plates using C 2 Cl 2 as the developing solvent. No partial credit is given to this question Answer: < < < lowest R f highest R f II. (9 points) Silica gel thin-layer chromatography (TLC) is often used to monitor the progress of an organic reaction. For the following ester hydrolysis reaction, a solvent system is selected to give the starting material an R f value of about 0.5. (1) Provide in the box below the structure of the expected product 7. (2) Fill in the spots that would be expected when the reaction is 50% compete and 100% complete. Make sure to assign each spot you draw to the corresponding compound number (5, 6, or 7). Consider only the compounds that can be visualized as a spot on TLC upon exposure of each solventdried plate to a 254 nm-uv lamp. C 3 2 S 4 (cat) 2 Δ (heat) % completion solvent front 100% completion n each TLC plate, a student has placed a sample of the starting material (5) as a reference on the left of the plate, a spot of the reaction mixture (after acidic workup) on the right, and a co-spot in the center of each. Co-spotting is where some of 5 and some of the reaction mixture are spotted together in order to make better comparisons. 5 co-spot 5 co-spot reaction mixture reaction mixture

3 216 S10-Exam #1 Page 3. Name III. (17 points) N-Benzylaniline can be prepared by reaction of benzyl chloride and aniline in the presence of aqueous sodium bicarbonate (NaC 3 ). Cl + N 2 + NaC 3 N + NaCl C 2 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, = 1, N = 14, = 16, Na = 23, Cl = 35.5 benzyl chloride: moles; aniline: moles; NaC 3 : moles (2) (2 points) What is the limiting reagent? (3) (3 points) What is the theoretical yield of N-benzylaniline? g (4) (2 points) What is the percentage yield of N-benzylaniline? % (5) (2 points) About 260 g of aniline can be recovered from the reaction. Does this affect the calculation of theoretical yield? Explain. (6) (2 points) What volume of benzyl chloride (density 1.10 g/ml) is required for the reaction? ml (7) (3 points) Why is it necessary to use such a large excess of aniline for the reaction? Explain.

4 216 S10-Exam #1 Page 4. Name IV. (18 points) For each of the following reactions, provide in the box below a step-by-step mechanism through the use of the curved-arrow convention. (1) C 3 NaB 4 ethanol Mechanism including the 3 + workup step: C workup (i.e., protonation) C 3 B Na C 3 7 (2) Mechanism: Ts * = Ts * (catalytic) benzene, reflux 4 h 3 C S (pka = ) + 2 Ts 11

5 216 S10-Exam #1 Page 5. Name V. (6 points) For each of the following sets of compounds, match the expected IR frequencies for the C= bond stretching vibration to the wavenumbers given. (1) 1694, 1686, or 1666 cm -1 3 C cm -1 cm -1 N cm -1 (2) 1763, 1719, or 1687 cm -1 2 N cm -1 cm -1 cm -1 VI. (3 points) A mixture of chlorobenzene (bp 132 C) and water (bp 100 C) could be steam distilled at 90 C. The vapor pressure of water at 90 C is measured to be 526 mmg. What would be the vapor pressure of chlorobenzene at 90 C? Write your answer in the box below. mmg VII. (12 points) For each of the following synthetic reactions, draw the structure of the expected product in the box provided. (1) N C C (2) 3 C C 3 + NaCl 3 C (solvent) NaCl (3) 3 C + 2 N Ts (catalytic) C 3

6 216 S10 Exam #1 Page 6 Name VIII. (12 points). Given below are infrared (IR) spectra of four compounds. The compounds are among those structures given on page 8. Assign each spectrum to its compound by putting the letter corresponding to the compound in the answer box next to the spectrum. The tables of characteristic infrared frequencies appear on pages 9 and 10. (1) (liquid film) Answer (2) (liquid film) Answer

7 216 S10 Exam #1 Page 7. VIII. (continued) Name (3) (liquid film) Answer (4) (KBr disc) Answer

8 216 S10 Exam #1 Page 8 Name VIII. (continued) A B I 3 C N 2 N C3 C C 3 J N C 3 C 3 C 3 D E F K L 3 C 3 C 3 C 3 C N N N G 3 C C 3 C 3 M 3 C 3 C 3 C C 3

(2) After dissolving a solid in a solvent at high temperature, the solution is not filtered.

(2) After dissolving a solid in a solvent at high temperature, the solution is not filtered. Name Key 216 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