In cells, vitamin C exists largely as its conjugate base X. X is an antioxidant because

Classify each radical as 1, 2, or 3. a. CH3CH2 CHCH2CH3 b. c. d.

Draw the most stable radical that can result from cleavage of a C H bond in each molecule. a. (CH3)2CHCH2CH3 b. (CH3)3CCH2CH3 c. (CH3)4C d.

Draw the products formed when a chlorine atom (Cl ) reacts with each species. a. CH3 CH3 b. CH2 CH2 c. Cl d. O2

Draw all constitutional isomers formed by monochlorination of each alkane. a. b. CH3CH2CH2CH2CH2CH3 c. (CH3)3CH

Compounds A and B are isomers having molecular formula C5H12. Heating A with Cl2 gives a single product of monohalogenation, whereas heating B under the same conditions forms three constitutional isomers. What are the structures of A and B?

Using Mechanism 15.1 as a guide, write the mechanism for the reaction of CH4 with Br2 to form CH3Br and HBr. Classify each step as initiation, propagation, or termination.

Calculate H for the two propagation steps in the reaction of CH4 with Br2 to form CH3Br and HBr (Problem 15.6).

Calculate H for the rate-determining step of the reaction of CH4 with I2. Explain why this result illustrates that this reaction is extremely slow.

Which C H bond in each compound is most readily broken during radical halogenation? a. b. c. CH3CH2CH2CH3

Why is the reaction of methylcyclohexane with Cl2 not a useful method to prepare 1-chloro-1- methylcyclohexane? What other constitutional isomers are formed in the reaction mixture?

Reaction of (CH3)3CH with Cl2 forms two products: (CH3)2CHCH2Cl (63%) and (CH3)3CCl (37%). Why is the major product formed by cleavage of the stronger 1 C H bond?

Synthesize each compound from (CH3)3CH. a. (CH3)3CBr b. (CH3)2C CH2 c. (CH3)3COH d. (CH3)2C(Cl)CH2Cl

Show all steps and reagents needed to convert cyclohexane into each compound: (a) the two enantiomers of trans-1,2-dibromocyclohexane; and (b) 1,2-epoxycyclohexane.

What products are formed from monochlorination of (2R)-2-bromobutane at C1 and C4? Assign R and S designations to each stereogenic center

Draw the monochlorination products formed when each compound is heated with Cl2. Include the stereochemistry at any stereogenic center. a. CH3CH2CH2CH2CH3 b. CH3 c. (CH3CH2)3CH d. (Consider attack at C2 and C3 only.) H Cl

Nitric oxide, NO , is another radical also thought to cause ozone destruction by a similar mechanism. One source of NO in the stratosphere is supersonic aircraft whose jet engines convert small amounts of N2 and O2 to NO . Write the propagation steps for the reaction of O3 with NO .

Draw a second resonance structure for each radical. Then draw the hybrid. a. CH3CH CH CH2 b. c. d

Draw the products of each reaction. a. h NBS b. h NBS CH2 CH CH3 c. Br2 CH2 CH CH3

Draw the structure of the four allylic halides formed when 3-methylcyclohexene undergoes allylic halogenation with NBS + h.

Which compounds can be prepared in good yield by allylic halogenation of an alkene? a. Br b. CH3CH2CH CHCH2Br c. Br

Draw a second resonance structure for the allylic radical formed as a product of Step [1] in Figure 15.8. What hydroperoxide is formed using this Lewis structure?

Which C H bond is most readily cleaved in linoleic acid? Draw all possible resonance structures for the resulting radical. Draw all the hydroperoxides formed by reaction of this resonancestabilized radical with O2. C O OH linoleic acid

Draw all resonance structures for the radical that results from hydrogen atom abstraction from BHT

Draw the product(s) formed when each alkene is treated with either [1] HBr alone; or [2] HBr in the presence of peroxides. a. CH2 CHCH2CH2CH2CH3 b. c. CH3CH CHCH2CH2CH3

When HBr adds to (CH3)2C CH2 under radical conditions, two radicals are possible products in the fi rst step of chain propagation. Draw the structure of both radicals and indicate which one is formed. Then draw the preferred product from HBr addition under radical conditions.

What reagents are needed to convert 1-ethylcyclohexene into (a) 1-bromo-2-ethylcyclohexane; (b) 1-bromo-1-ethylcyclohexane; (c) 1,2-dibromo-1-ethylcyclohexane?

Draw an energy diagram for the two propagation steps in the radical addition of HBr to propene. Draw the transition state for each step.

Draw the steps of the mechanism that converts vinyl chloride (CH2 CHCl) into poly(vinyl chloride).

With reference to the indicated C H bonds in 2-methylbutane: 2 CCH CH CH3 CH3 [1] [2] [3] HH 2-methylbutane H a. Rank the C H bonds in order of increasing bond strength. b. Draw the radical resulting from cleavage of each C H bond, and classify it as 1, 2, or 3. c. Rank the radicals in order of increasing stability. d. Rank the C H bonds in order of increasing ease of H abstraction in a radical halogenation reaction.

Rank each group of radicals in order of increasing stability. a. (CH3)2CCH2CH(CH3)2 (CH3)2CHCHCH(CH3)2 (CH3)2CHCH2CH(CH3)CH2 b.

Why is a benzylic C H bond unusually weak? benzylic C CH2 H H bond

Rank the indicated hydrogen atoms in order of increasing ease of abstraction in a radical halogenation reaction. CH2 H Hc Hb H Hd CHCHCHC(CH3)CH2 Ha H H

Draw all constitutional isomers formed by monochlorination of each alkane with Cl2 and h. a. b. (CH3)3CCH2CH2CH2CH3 c. d. CH3

What is the major monobromination product formed by heating each alkane with Br2? a. b. (CH3)3CCH2CH(CH3)2 c. CH3 d. (CH3)3CCH2CH3

Five isomeric alkanes (AE) having the molecular formula C6H14 are each treated with Cl2 + h to give alkyl halides having molecular formula C6H13Cl. A yields fi ve constitutional isomers. B yields four constitutional isomers. C yields two constitutional isomers. D yields three constitutional isomers, two of which possess stereogenic centers. E yields three constitutional isomers, only one of which possesses a stereogenic center. Identify the structures of AE.

What alkane is needed to make each alkyl halide by radical halogenation? a. Cl b. Br c. Br d. (CH3)3CCH2Cl

Explain why chlorination of cyclohexane with two equivalents of Cl2 in the presence of light is a poor method to prepare 1,2-dichlorocyclohexane.

Explain why radical bromination of p-xylene forms C rather than D. CH3 Br2 p-xylene Br NOT formed C D CH3 CH3 CH2Br CH3 CH3

a. What product(s) (excluding stereoisomers) are formed when Y is heated with Cl2? b. What product(s) (excluding stereoisomers) are formed when Y is heated with Br2? c. What steps are needed to convert Y to the alkene Z? Y Z

Draw resonance structures for each radical. a. CH2 b. c.

Draw the products formed when each alkene is treated with NBS + h. a. b. CH3CH2CH CHCH2CH3 c. (CH3)2C CHCH3 d.

Is it possible to prepare 5-bromo-1-methylcyclopentene in good yield by allylic bromination of 1-methylcyclopentene? Explain.

Draw all constitutional isomers formed when X is treated with NBS + h. X

Draw the organic products formed in each reaction. a. h Cl2 d. h NBS CH2 g. HBr ROOR CH2 b. Br2 CH3 CH3 CH3 e. HBr h. Br2 c. h Br2 f. HBr ROOR i. h NBS

What reagents are needed to convert cyclopentene into (a) bromocyclopentane; (b) trans-1,2-dibromocyclopentane; (c) 3-bromocyclopentene?

Draw the products formed in each reaction and include the stereochemistry around any stereogenic centers. a. h Br2 CH3 c. h Cl2 e. Br2 H b. h Cl2 CH3 d. h Br2 CH3 CH3 CH3 f. Cl2 CH3CH2 CCl3 F H C

(a) Draw all stereoisomers of molecular formula C5H10Cl2 formed when (2R)-2-chloropentane is heated with Cl2. (b) Assuming that products having different physical properties can be separated into fractions by some physical method (such as fractional distillation), how many different fractions would be obtained? (c) Which of these fractions would be optically active?

(a) Draw all stereoisomers of molecular formula C7H15Cl formed when (3S)-3-methylhexane is heated with Cl2. (b) Assuming that products having different physical properties can be separated by fractional distillation, how many different fractions would be obtained? (c) How many fractions would be optically active?

Draw the six products (including stereoisomers) formed when A is treated with NBS + h. CH2 A

Consider the following bromination: (CH3)3CH + Br2 (CH3)3CBr + HBr. a. Calculate H for this reaction by using the bond dissociation energies in Table 6.2. b. Draw out a stepwise mechanism for the reaction, including the initiation, propagation, and termination steps. c. Calculate H for each propagation step. d. Draw an energy diagram for the propagation steps. e. Draw the structure of the transition state of each propagation step.

Draw a stepwise mechanism for the following reaction. h NBS Br Br + + HBr

Although CH4 reacts with Cl2 to form CH3Cl and HCl, the corresponding reaction of CH4 with I2 does not occur at an appreciable rate, even though the I I bond is much weaker than the Cl Cl bond. Explain why this is so.

An alternative mechanism for the propagation steps in the radical chlorination of CH4 is drawn below. Calculate H for these steps and explain why this pathway is unlikely. CH4 + + Cl CH3Cl H Cl Cl H + + 2

When 3,3-dimethyl-1-butene is treated with HBr alone, the major product is 2-bromo-2,3-dimethylbutane. When the same alkene is treated with HBr and peroxide, the sole product is 1-bromo-3,3-dimethylbutane. Explain these results by referring to the mechanisms.

Write out the two propagation steps for the addition of HCl to propene and calculate H for each step. Which step prohibits chain propagation from repeatedly occurring?

Devise a synthesis of each compound from cyclopentane and any other required organic or inorganic reagents. a. Cl c. Br e. Cl Cl g. Br Br Br i. OH O b. d. OH f. O h. OH j. OH CN

Devise a synthesis of each target compound from methylcyclohexane. You may use any other required organic or inorganic reagents. a. OH b. O c. Cl + Cl enantiomer

Devise a synthesis of each target compound from the indicated starting material. You may use any other required organic or inorganic reagents. a. CH3C CH CH3CH2CH3 b. Br Br c. Br CHHC

Devise a synthesis of each compound using CH3CH3 as the only source of carbon atoms. You may use any other required organic or inorganic reagents. a. HC CH b. HC CCH2CH3 c. HC CCH2CH2OH d. e. O

Devise a synthesis of OHC(CH2)4CHO from cyclohexane using any required organic or inorganic reagents.

As described in Section 9.16, the leukotrienes, important components in the asthmatic response, are synthesized from arachidonic acid via the hydroperoxide 5-HPETE. Write a stepwise mechanism for the conversion of arachidonic acid to 5-HPETE with O2. COOH C5H11 arachidonic acid 5-HPETE leukotriene C4 O2 COOH C5H11 OOH C5H11 RSH several steps S R COOH OH

Ethers are oxidized with O2 to form hydroperoxides that decompose violently when heated. Draw a stepwise mechanism for this reaction. O2 O O unstable hydroperoxide OOH

(a) Ignoring stereoisomers, what two allylic hydroperoxides are formed by the oxidation of 1-hexene with O2? (b) Draw a stepwise mechanism that shows how these hydroperoxides are formed.

In cells, vitamin C exists largely as its conjugate base X. X is an antioxidant because radicals formed in oxidation processes abstract the indicated H atom, forming a new radical that halts oxidation. Draw the structure of the radical formed by H abstraction, and explain why this H atom is most easily removed. vitamin C X HO OH O OH HO O OH O O OH HO O

What monomer is needed to form each polymer? a. polyisobutylene (used to make basketballs) b. COOEt COOEt poly(ethyl acrylate) (used in latex paints) COOEt Et = CH2CH3

(a) Hard contact lenses, which fi rst became popular in the 1960s, were made by polymerizing methyl methacrylate [CH2 C(CH3)CO2CH3] to form poly(methyl methacrylate) (PMMA). Draw the structure of PMMA. (b) More comfortable softer contact lenses introduced in the 1970s were made by polymerizing hydroxyethyl methacrylate [CH2 C(CH3)CO2CH2CH2OH] to form poly(hydroxyethyl methacrylate) (poly-HEMA). Draw the structure of poly-HEMA. Since neither polymer allows oxygen from the air to pass through to the retina, newer contact lenses that are both comfortable and oxygen-permeable have now been developed.

Draw a stepwise mechanism for the following polymerization reaction. CH2 CHCN ROOR CN CN CN

As we will learn in Section 30.2C, styrene derivatives such as A can be polymerized by way of cationic rather than radical intermediates. Cationic polymerization is an example of electrophilic addition to an alkene involving carbocations. CH CH2 A CH3O a. Draw a short segment of the polymer formed by the polymerization of A. b. Why does A react faster than styrene (C6H5CH CH2) in a cationic polymerization?

A and B, isomers of molecular formula C3H5Cl3, are formed by the radical chlorination of a dihalide C of molecular formula C3H6Cl2. a. Identify the structures of A and B from the following 1 H NMR data: Compound A: singlet at 2.23 and singlet at 4.04 ppm Compound B: doublet at 1.69, multiplet at 4.34, and doublet at 5.85 ppm b. What is the structure of C?

Identify the structure of a minor product formed from the radical chlorination of propane, which has molecular formula C3H6Cl2 and exhibits the given 1 H NMR spectrum. 876543210 ppm

Radical chlorination of CH3CH3 forms two minor products X and Y of molecular formula C2H4Cl2. a. Identify the structures of X and Y from the following 1 H NMR data: Compound X: singlet at 3.7 ppm Compound Y: doublet at 2.1 and quartet at 5.9 ppm b. Draw a stepwise mechanism that shows how each product is formed from CH3CH3.

Draw a stepwise mechanism for the following addition reaction to an alkene. O CH3 H C + ROOR O

PGF2 (Sections 4.15 and 29.6) is synthesized in cells from arachidonic acid (C20H32O2) using a cyclooxygenase enzyme that catalyzes a multistep radical pathway. Part of this process involves the conversion of radical A to PGG2, an unstable intermediate, which is then transformed to PGF2 and other prostaglandins. Draw a stepwise mechanism for the conversion of A to PGG2. (Hint: The mechanism begins with radical addition to a carboncarbon double bond to form a resonance-stabilized radical.) CO2H O O O O O2 COOH OOH PGG2 unstable intermediate A PGF2 HO COOH OH HO