Lab Exam - Question 1 continues Quesmm 1 continues _ I . i)...

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Unformatted text preview: Question 1 continues Quesmm 1 continues _ I . i) When this reaction is carried out for a much longer period of time and at higher temperature, a f) When this reaction is cued out for a much longer pemd Ohms and at hlgher temperame’ a dinitzmtion product is formed. Give the structure of this dinitration product and explain why it is formed dinitration product is formed. Give the structure of this dinitration product and explain why it is formed quite Slowly. [2 points] quite slowly. [2 points] Question 2. Quesnon 2- a) When 4-methyl~l-nitrobenzene is heated with KMnO4 and NaOH , the major product isolated after a) When 4-methyl~l-nitrobenzene is heated with KMnOr and NaOH , the major product isolated after appropfim mpulafion is 7 [2 points] appropriate manipulation is ? [2 pomts] b) The students who carried out this reaction heated the reaction mixture for about 2 hours. At the b) The students who carried out this reaction heated the reaction mixture for about 2 hours. At the end of the reaction time the colour of the reaction mixture was still purple. end of the reaction time the colour of the reaction mixture was still purple. What gives the reaction mixture the purple colour? [1 point] What gives the reaction mixture the purple colour? [1 point] _ c) What reagent can be added to discharge the pmple colour? [I point] c) What reagent can be added to discharge the purple colour? [1 pomt] C!) After the brown precipitate that had formed during the reaction and the discoloration process was d) After the brown precipitate that had formed during the reaction and the discoloration process was final-ed Off and the aqueous filmte was acidified filtered Off and the aqueous filtrate was ac‘d‘fied . . _ What chemistry happens during the acidification process. Give the equation.[ 2 points] What chemistry happens during the acidification process. Give the equatron.[ 2 pomts] Question 3. Furfural, (1) , when reacted with compound 2 and 10% NaOH in a mixture of ethanol and water gives a product (4) with molecular formula C “HHOZ. CH3 1%N OH 6—40 + 0 a 7 C14H1403 ——> Ct4H1202 H Ethanol-water [2:1] (4) (1) 0 CH3 ‘3’ (2) a) What type of reaction is being performed ? [1 point] b) What is the function of the 10% NaOH in this reaction. Answer with an equation. [1 point] c) What is the structure of the intermediate product (3). Give the complete mechanism for its formation. [3 points] (1) A student tried this reaction using only water rather than the ethanol/water mixture. The experiment worked only very poorly. Explain why? [2 points] e) A pair of students came late to the lab. They quickly washed the dirty equipment left in their locker by the previous group with soap and water and rinsed it with acetone. They then proceeded quickly to carry out the experiment. They discovered that the yield of the desired product was low. Give a plausible explanation for their result. [2 points] Question 4. You have planned to carry out the interconversion of compound (A) to ((B). NC A H3C ( ) H30 (B) What type of reaction is required here? [lpoint] What reagents and /or catalysts are required to achieve the desired transformation? [2 points] Unfortunately, after the reaction was supposedly complete, workup yielded a mixture that was mamly product, but it also contained about 20% of starting material Outline a procedure, based on a chemical reaction, which could be could be used to separate the desued product fiom the unreacted starting material (A) . Draw the reaction and outline clearly the steps in the procedure. [ 4 points] d) The reaction of the amine (B) with acetic anhydride is best carried out in an aqueous buffer solution at a pH around 8-9. 1) Give the product and show the mechanism for its fonnation [3 points] Question 4d continues ii) When the pH of the solution is approximately 1, no acetanilide is formed Explain with an equation. [1 point] iii) When the pH of the solution is 14 only a small amount of acetanilide is formed. Explain why. Use an equation to illustrate your answer. [1 point] Question 5. a) Give a general structure of soap and explain the features of the structure that make it useful as a soap. [3 points] b) Soaps do not work as well in hard as’in soft water. What is the basis of the difference. Explain using chemical equation(s) [ 2 points] d) Give the structure, or the name, of a common unsaturated fatty acid. [1 point] Question 6 ~ The esterificiation of 3-bromobenzoic acid with methanol results in the formanon of (I). OCH3 0 QA (I) Br a) Draw the complete overall reaction showing all the features for the formation of [2 points] b) Give the mechanism for the formation of the product [3 points] c) The reaction is carried out by refluxing a solution of 5.03 grams of benzoic w in 10.0 g of methanol containing 1 mL of concentrated H2804 for lhour and then cooling the mixture. A viable workup procedure is described below. “ the cooled reaction mixture is poured into a separatory funnel contained 25 mL of ether. The mixture is washed with 25 ml of water. The ether layer is then washed tow times with 10 mL of 10% sodium bicarbonate solution. The ether layer is then dried over anhydrous Na2504 and the solvent is evaporated to yield 4.84 grams of product that was shown by NMR spectroscopy to be pure methyl benzoate”. i) What is the purpose ofwashjng the mixture first with water. [1 point] ii) What is accomplished by washing with sodium bicarbonate solution? Answer with an equation, if you think it appropriate. [2 points] Question Go continues iii) Suppose that the 4.84 g of ethyl benzoate isolated represented exactly the yield of (I) forme equilibrium in the above reaction. Calculate the equilibrium constant for the above esterification reaction. SHOW THE CALCULATIONS. [3 points] K: t) Calculate the % yield obtained for (I) in the above reaction based on the data given. SHOW THE CALCULATIONS. [2 points] % yield = Question 7. Quckies!! [1 point each] a) What is the major constituent of silica gel? b) Why is a mixture of water and dichloromethane not useful for recrystallizing PhCHzOH ? c) Give the general structure of the organic compounds that can undergo the Haloform reaction. (1) The Haloform reaction results in an oxidation of the organic compound. What i the oxiding agent that is commonly used? Question 8. The complete hydrolysis of an ester such as (H) is best carried out with 2M NaOH in a mixture of methanol-water or ethanol—water. CL 0 0% + NaOH 7 a I) methanol-water a) Give the structure of all of the products expected. [2 points] Question 7 continues b) Why is this reaction irreversible? Use a structure or equation and words to give your answer. [2 points] c) How much of the 2.0 molar NaOH solution is needed to hydrolyze completely 5.25 g of compound II? [2 points]. Show the calculations. Answer: d) Suppose the progress of the above reaction were followed by TLC and the Rf of the starting material (11) is 0.8 using a 1:1 mixture of hexane and ethyl acetate. i) Sketch the expected TLC on the drawing below for the pure starting material AND when the reaction is about 50% complete. IDENTIFY ALL THE COMPONENTS ON THE TLC PLATE and estimate approximately the Rf s of the predicted product(s). [3 points] 10 PS“- : Y5 : start finish Direction of the flow mm, X = pure starting material Y = reaction mixture at 50% completion. Question 7d continues (ii) Suppose the developing solvent is changed from 1:1 hexane-ethyl acetate to 1:2 hexane ethyl acetate. [1 point] Sketch the changes expected in the ‘50% reaction’ TLC on the diagram below AND give a very brief explanation. [I point] start finish Direction of the flow a Y = 50 % reaction Question 8. The oxidation of 2.15 g of the primary alcohol (L) was carried out with sodium dichromate catalyzed by sulfuric acid in a mixture of diethyl ether and water. The products , isolated after 30 min. of reaction time were a mixture of the 0.62 g of the aldehyde (M) and 0.84 g of the acid (N). a) Give the structure of the key intermediate in the oxidation of (L) to (M). [2 points] b) Water plays a crucial role in the oxidation of (M) to (N). Explain with the aid of a structure. [2 points] 11 c) Calculate the experimental yield obtained for the acid (N). [2 points] % yield of (N): Question 8 continues (1) Suppose that the reaction time was extended form 30 min to 1 hour. How would the results have changed with respect to (M) and (N)? Explain your answer. [2 points] Question 9. - _ A . ‘th The isomen'zation of Z- isomer, dimethyl maleate, to its E- isomer 15 carried out w1 Brz as catalyst in the presence of light. ‘ _ ‘ ‘ _ 9 a) Why can Z-2 —butene not be isomerized to its E-isomer usmg the same technique. Explain by showing carefully what happens in this case. [3 points] uestion 10. . _ _ giggest a method, based on a chemical test, for differentiating each of the followmg pairs of compounds. Give clearly the visual change that can he used to make the decision. [2 points each] 538.8.“ Hm E 30: was 8365 «EH .3 egosbm 9: mm “mg .02 E mu 325an 330308 a fig 83th 9593 a 330$ BEL .mmouxu 30m min?” a: noun“. 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Lab Exam - Question 1 continues Quesmm 1 continues _ I . i)...

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