much more stable then the

Transcription

1 8.1 Give the structure and name of the product that would be obtained from the ionic addition of I to propene. I I I 8.3 Provide mechanistic explanations for the following observations:(a)the addition of hydrogen chloride to 3-methyl-1-butene produces two products : 2-chloro-3-methylbutane and 2-chloro-2-methylbutane. (b) The addition of hydrogen chloride to 3,3-dimethyl-1-butene produces two products: 3-chloro-2,2-dimethylbutane and 2-chloro-2,3-dimethylbutane. (The first explanations for the course of both of these reactions were provide by F. Whitmore; see Section 7.7A.) (a) step 1: ; Because the step 2: much more stable then the l - l ; l Me l

2 (b) step 1: rearrangement: Because the much more stable then the Step 2: l l - ; l - Me l 8.4 In one industrial synthesis of ethanol, ethene is first dissolved in 95% sulfuric acid. In a second step water is added and the mixture is heated. utline the reactions involved. S utline all steps in a mechanism showing how 2,3-dimethyl-2-butanol is formed in the acid-catalyzed hydration of 3,3-dimethyl-1-butene.

3 STEP slow STEP2 3 3 FAST (Rearrangement) STEP FAST STEP FAST The following order of reactivity is observed when the following alkenes are subjected to acid-catalyzed hydration. ( 3 ) 2 2 > 3 2 > 2 2 Explain this order of reactivity. The mechanism of hydration is to form carbocation. For the stability of the carboation is: ( 3 ) 2 3 > 3 3 > 2 3 So the ( 3 ) 2 3 is the most stable, has the lowest energy, and the ( 3 ) 2 2 has the highest reactivity. And the 2 2 has the lowest reactivity. 8.8 When 2-methylpropene (isobutylene) is dissolved in methanol containing a strong acid, a reaction takes place to produce tert-butyl methyl ether, 3 ( 3 ) 3. Write a mechanism that accounts for this.

4 A In section 8.7 you studied a mechanism for the formation of one enantiomer of trans-1, 2-dibromocyclopentane when bromine adds to cyclopentene. Now write a mechanism showing how the other enantionmer forms utline a mechanism that account for the formation of trans-2-bromocyclopentanol and its enantiomer when cyclopentene is treated with an aqueous solution of bromine When ethene gas is passed into an aqueous solution containing bromine and sodium chloride, the products of the reaction are 2 2, 2 2, and 2 2 l. Write

5 mechanisms showing each product is formed; Step1: _ 2 2 Step2: l l 2 2

6 What products would you expect from each of the following reactions? (a) trans-2-butene (b) K( 3 ) 3 l 3 yclopentene K( 3) 3 3 (c) cis-2-butene (a) 3 2 I 2 /Zn(u) diethylether K( 3 ) 3 l 3 (b) l l enantiomer K( 3 ) 3 3 (c) I 2 /Zn(u) diethylether Starting with cyclohexene and using any other needed reagents, outline a synthesis of

7 7,7-dibromobicyclo[4.1.0]heptane. K(3) Treating cyclohexene with 1,1-diiodoethane and a zinc-copper couple leads to two isomeric products. What are their structures? I 3 Zn(u) I Starting with an alkene, outline syntheses of each of the following: 3 (a) (b) (c)

8 (a) 3 KMn 4 -, 2 (b) 3 2 KMn 4 -, 2 enantiomer (c) KMn 4 -, 2 enantiomer 8.16 Explain the following facts: (a) Treating (Z)-2-butene with s 4 in pyridine and then NaS 3 in water gives a diol that optically inactive and cannot be resolved. (b) Treating (E)-2-butene with s 4 and then NaS 3 gives a diol that optically inactive but can be resolved into enantiomers.

9 3 3 3 s 4 NaS 3 3 meso s 4 3 ( ) 3 NaS Write the structure of the alkenes that would produce the following products when treated with ozone and then with zinc and acetic acid. ( a ) 3 3 and 3 ( 3 ) ( b ) 3 2 only ( 2 mol produced from 1 mol of alkene ) ( c ) and Alkynes A and B have the molecular formula Treating either compound A or B with excess hydrogen in the presence of a metal catalyst leads to the formation of octane. Similar treatment of a compound ( 8 12 ) leads to a product with the formula Treating alkyne A

10 with ozone and then acetic acid furnishes a single product Treating alkyne with ozone and then water produces a single product 2 ( 2 ) 6 2,. ompound B has an absorption in its IR spectrum at ~3300cm -1, what are compounds A,B and. A: B: : 8.21 White structural formulas for the products that form when 1-butene reacts with each of the following reagents: (a) I I (b) 2, Pt (c) Dilute 2 S 4, warm (d) old concentrated 2 S

11 S (e) old concentrated 2 S 4, then 2 and heat (f) in the presence of alumina (g) 2 in l 4 (h) 2 in l 4, then KI in acetone (i) 2 in 2

12 (j) l in the presence of alumina l (k) old dilute KMn 4, - (l) 3, then Zn, Ac, (m) s 4, then NaS 3 / 2 (n) Kmn 4, -, heat, then White structural formulas for the products that form when cyclohexene reacts with each of the following reagents:

13 (o) I I (p) 2, Pt (q) Dilute 2 S 4, warm (r) old concentrated 2 S S (s) old concentrated 2 S 4, then 2 and heat

14 (t) in the presence of alumina (u) 2 in l 4 (v) 2 in l 4, then KI in acetone (w) 2 in 2

15 (x) l in the presence of alumina l (y) old dilute KMn 4, - (z) 3, then Zn, Ac (aa) s 4, then NaS 3 / 2 (bb) Kmn 4, -, heat, then 3

16 8.23 Give the structure of the products that you would expect from the reaction of 1-butyne with: (a) ne molar equivalent of 2 (b) ne molar equivalent of in the presence of alumina (c) Two molar equivalent of in the presence of alumina (d) 2 (in excess)/pt (e) 2, Ni 2 B (P-2) (f) NaN 2 in liquid N 3, then 3 I (g) NaN 2 in liquid N 3, then ( 3 ) 3 (a) (b) (c) (d) (e)

17 (f) (g) Na 8.24 Give the structure of the products you would expect from the reaction (if any) of 2-butyne with: (a) ne molar equivalent of in the presence of alumina (b) Two molar equivalents of in the presence of alumina (c) ne molar equivalent of 2 (d) Two molar equivalents of 2 (e) 2, Ni 2 B (P-2) (f) ne molar equivalent of l in the presence of alumina (g) Li/liquid N 3 (h) 2 (in excess)/pt (i) Two molar equivalents of 2, Pt (j) KMn 4, -, then 3 (k) 3, Ac (l) NaN 2, liquid N 3 Answers: (a) 3 3 (b)

18 3 3 (c) 3 3 (d) 3 3 (e) 3 3 (f) l 3 3 (g) 3 (h) (i) 3 3

19 (j) (k) 3 (two molar equivalents) 3 (two molar equivalents) (l) I think they cannot react with each other in this condition show how 1-butyne could be synthesized from each of the follow: (a) 1-butene (b) 1-chlorobutane (c) 1-chloro-1-butene (d) 1, 1-dichlorobutane (e) Ethyne and ethylbramide (a) 2 / l 4 3 NaN 2 Na N 4 l (b) l t-buk t-bu then as in (a) (c) l 2 NaN 2 Na N 4 l l (d) l 3 NaN 2 Na N 4 l (e) NaN Starting with 2-methylpropene (isobutylene) and using any other needed reagents, outline a synthesis of each of the following: (a) ( 3 ) 3 (b) ( 3 ) 3 l (c) ( 3 ) 3 (d) ( 3 ) 3 F (e) ( 3 ) 2 () 2 l Answer (a) ( 3 ) 2 = 2 2 (b) ( 3 ) 2 = 2 l 60% 2 S 4 (3 ) 3-30 o ( 3 ) 3 l

20 (c) ( 3 ) 2 = 2 (d) ( 3 ) 2 = 2 F (e) ( 3) 2 = 2 l 2 2 ( 3 ) 3 ( 3 ) 3 F ( 3 ) 2 () 2 l 8.27 Myrcene, a fragrant compound found in bayberry wax, has the formula 1016 and is known not to contain any triple bonds. (a) What is the index of hydrogen deficiency of myrecene? When treated with excess hydrogen and a platinum catalyst, myrcene is converted to a compound A with the formular (b) ow many rings does myrcene contain? (c) ow many double bonds? ompound Acan be identified as 2,6-dimethyloctane. zonolysis of myrcene followed by treatment with zinc and acetic acid yields 2 mol of formaldehyde (), 1 mol of acetone (), and a third compound Bwith the formula 563. (d) What is the structure of myrcene? (e) f compound B? (a) 3 (b) No (c) 3 (d) (e) 8.28 When propene is treated with hydrogen chloride in ethanol, one of the products of the reaction is ethyl isopropyl ether. Write a plausible mechanism that accounts for the formation of this product. Step 1: 3 2 l 3 3 l Step 2:

21 Step 3: When, in separate reactions, 2-methylpropene, propene, and ethene are allowed to react with I under the same conditions (i.e., identical concentration and temperature), 2-methylpropene is found to react fastest and ethene slowest. Provide an explanation for these relative rates. According to Markovnikov rule, in the addition of I to the alkenes, the hydrogen atom adds to the carbon atom of the double bond that already has the greater number of hydrogen atoms. The reactions take place 3 2 I 3 3 I I 3 3 I I 3 2 I - Because the 3 0 carbocation is the most stable carbocation and the 2 0 carbocation is more stable than the 1 0 carbocation, the free energy in each reaction is 3 0 carbocation<2 0 carbocation<1 0 carbocation. As a result, the 2-methylpropene found to react fastest and ethene slowest Farnesene (below) is a compound found in the waxy coating of apples. Give the structure and IUPA name of the product formed when farnesene is allowed to react with excess hydrogen in the presence of a platinum catalyst. Farnesene 3 (S)-2,6,10-Trimethyl-dodecane

22 3 (R)-2,6,10-Trimethyl-dodecane 8.31 Write structural formulas for the products that would be formed when geranial, a component of lemongrass oil, is treated with ozone and then with zinc and water. The structure formulas for the products are the followings: & & 8.32 Limonene is a compound found in orange oil and lemon oil. When limonene is treated with excess hydrogen and a platinum catalyst, the product of the reaction is 1-isopropyl-4-methylcyclohexane. When limonene is treated with ozone and then with zinc and water the products of the reaction are and the following compound. Write a structural formula for limonene. The structural formula is: 8.33 When 2,2-diphenyl-1-ethanol is treated with aqueous I, the main product of the reaction is 1-iodo-1,1-diphenylethane. Propose a plausible mechanism that accounts for this product.

23 I 2 Ph I aqueous 3 Ph (main product) Ph Mechanism: Ph 2 Ph I aqueous 2 Ph I - Ph 2 Ph 2 Ph 2 Ph 2 2 Ph Ph 2 Ph 3 Ph Ph Ph I 3 Ph I - 3 Ph Ph Ph 8.34 When 3,3-dimethyl-2-butanol is treated with concentrated I, a rearrangement takes place. Which alkyl iodide would you expect from the reaction? (Show the mechanism by which it is formed.) The main product of the reaction is 3,3-dimethyl-2-iodobutane. 2 I 8.35 Pheromones are substances secreted by animals that produce a specific behavioral response in other members of the same species. Pheromones are effective at very low concentrations and include sex attractants, warning substances, and aggregation compounds. The sex attractant pheromone of the codling moth has the molecular formula n catalytic hydrogenation

24 this pheromone absorbs two molar equivalents of hydrogen and is converted to 3-ethyl-7-methyl-1-decanol. n treatment with ozone followed by treatment with zinc and water the pheromone produce , , and 2. (a) Neglecting the stereochemistry of the double bonds, write general structure for this pheromone. (b) The double bonds are known to be (2Z, 6E). Write a stereo-chemical formula for the codling moth sex attractant. (a) (b) 8.36.The sex attractant of the common housefly (Musca domestica) is a compound called muscalure. Muscalure is ( 2 ) 12 ( 2 ) 7. Starting with ethyne and any other needed reagents, outline a possible synthesis of muscalure. Solution: NaN 2 3 ( 2 ) 6 2 (2 ) 7 3 NaN 2 ( 2 ) ( 2 ) ( 2 ) 12 ( 2 ) 3 Pb/BaS 4 2 ( 2 ) 12 ( 2 ) 7

25 8.37 Starting with ethyne and 1-bromopentane as your only organic reagents (except for solvents) and using any needed inorganic compounds, outline a synthesis of the compound shown below. Na N 2 liq.n 3-33 Na Na Shown below is the final step in a synthesis of an important perfume constituent, cis-jasmone. Which reagents would you choose to carry out this last step? ANSWER: The reagents should be (1) Raney Nickel / Write stereochemical formulas for all of the products that you would expect from each of the following reactions. (You may find models helpful.) (a) (b) s 4 NaS 3,

26 3 s NaS 3, (c) ,l (d) ,l When cyclohexene is allowed to react with bromine in an aqueous solution of sodium chloride, the products are trans-1,2-dibromocyclohexane, trans-2-bromo-cyclohexanol, and trans-1-bromo-2-chlorocyclohexane. Write a plausible mechanism that explains the formation of this last product. Nu l l 8.42 Predict features of their IR spectra that you could use to distinguish between the members of the following pairs of compounds. (a) Pentane and 1-pentyne (b) Pentane and 1-pentene

27 (c) 1-Pentene and 1-pentyne (d) Pentane and 1-bromopentane (e) 2-pentyne and 1-pentyne (f) 1-Pentene and 1-pentanol (g) Pentane and 1-pentanol (h) 1-omo-2-pentene and 1-bromopentane (i) 1-Pentanol and 2-penten-1-ol (a) 1-pentyne ( ) has an absorbing peak about cm -1 ( ) and about 3300cm -1 ( ). (b) 1-pentene ( ) has an absorbing peak around cm -1 ( ) and about cm -1 ( ). (c) 1-pentene ( ) has an absorbing peak in cm -1 ( ) and about cm -1 ( ), but 1-pentyne ( ) has an absorbing peak around cm -1 ( ) and about 3300cm -1 ( ). (d) 1-bromopentane ( ) has an absorption around cm -1 ( ). (e) 2-Pentyne ( ) has cm -1 ( ), but 1-pentyne ( ) has 3300cm -1 ( ). (f) 1-Pentene ( ) has cm -1 ( ) and about cm -1 ( ), but 1-pentanol ( ) has a broad absorption peak cm -1 (). (g) 1-pentanol ( ) has a broad band peak around cm -1 ().

28 (h) 1-omo-2-pentene ( ) has a double bond peak around cm -1 ( ), but 1-bromopentane doesn t have. (i) 2-penten-1-ol has a double bond peak around cm -1 ( ), but 1-pentanol doesn t have The double bond of tetrachloroethene is undetectable in the bromine/carbon tetrachloride test for unsaturation. Give a plausible explanation for this behavior. Because of the electron-withdrawing nature of chlorine, the density at the double bond is greatly reduced and attacked by the electrophilic bromine doesn t occur Three compounds A, B, and all have the formula All three compounds rapidly decolorize bromine in L 4 ; all three are soluble in cold concentrated sulfuric acid. ompound A has an absorption in its IR spectrum at about 3300cm -1, but compound B and do not. ompounds A and B both yield hexane when they are treat with excess hydrogen in the presence of a platinum catalyst. Under these condition absorb only one molar equivalent of hydrogen and gives a product with the formula When A is oxidized with hot basic potassium permanganate and the resulting solution acidified, the only organic product that can be isolated is 3 ( 2 ) 3 2. Similar oxidation of B gives only 3 2 2, and similar treatment of gives only 2 ( 2 ) 4 2. What are structures for A, B, and? A: B: : 3-hexyne 8.47 Use your answer to the preceding problem to predict the stereochemistry outcome of the addition of bromine to maleic acid and to fumaric acid. (a) Which dicarbonoxylic acid would add bromine to

29 yield a meso compound? (b) Which will yield a racemic form? maleic acid fumaric acid meso compound: racemic form: 2 meso compound 2 racemic form 8.48 An optically active compound A (assume that it is dextrorotatory) has the molecular formula A reacts with hydrogen bromide, in the absence of peroxides, to yield isomeric products, B and, with the molecular formula ompound B is optically active; is not. Treating B with 1 mol of potassium tert-butoxide yields ()-A. Treating with 1 mol of potassium tert-butoxide yields ()-A. Treating A with potassium tert-butoxide yields D ( 7 10 ). Subjecting 1 mol of D to ozonolysis followed by treatment with zinc and acetic acid yields 2 mol of formaldehyde and 1 mol of 1,3-cyclopentanedione. 1,3-yclopentanedione Propose stereo chemical formulas for A, B,, and D and outline the reactions involved in these transformations.

30 ()-A B t-buk ()-A ()-A t-buk 3 3 ()-A 2 2 (-)-A 3 ()-A 2 t-buk 2 D 2 1, 3 2, Zn, Ac 8.49 A naturally occurring antibiotic called mycomycin has the structure shown here. Mycomycin is optically active. Explain this by writing structures for the enantiomeric forms of mycomycin. 2 The stereo structure for this molecule is 2 The enantiomeric form is An optically active compound D has the molecular formula 6 10 and shows a peak at about 3300 cm -1 in its IR spectrum. n catalytic hydrogenation D yields E ( 6 14 ). ompound E is

31 optically inactive and cannot be resolved. Propose structures for D and E. Answers: D should be 3 E should be ; (a) By analogy with the mechanism of bromine addition to alkenes, draw the likely three-dimensional structures of A, B, and. Reaction of cyclopentene with bromine in water gives A. Reaction of A with aqueous Na (1 equivalent, cold) gives B, 5 8 (no 3590 to 3650 cm-1 infrared absorption). (See the squalene cyclization discussion for a hint.) eating of B in methanol containing a catalytic amount of strong acid gives, , which does show 3590 to 3650 cm-1 infrared absorption. (b) Specify the R or S configuration of the stereocenters in your predicted structures for. Would it be formed as a single stereocenter or as a racemate? (c) ow could you experimentally confirm your predictions about the stereochemistry of? A & B 3 3 S S R R (c), in contrast to its cis isomers, would exhibit no intramolecular hydrogen bonding, this would be proven by the absence of infrared absorption in the cm -1 region when studied as a very dilute solution in l 4. would only show free stretch at about 3625 cm Triethylamine, ( 2 5 ) 3 N, like all amines, has a nitrogen atom that has an unshared pair of

32 electrons. Dichlorocarbene also has an unshared pair of electrons. Both can be represented as shown below. Draw the structures of compounds Q, E, and R. ( 2 5 ) 3 N l 2 D (an unstable adduct) Q E 2 4 (by an intramolecular E 2 reaction) E 2 l N l R (Water effects a replacement that is the reverse of that used to make gem-dichlorides.) l N N l l 2 N l 2 N l N N