SN1 substitution and E1 elimination frequently compete in

Classify each compound as an alkyl halide, a vinyl halide, or an aryl halide. Equation Transcription: Text Transcription: CH3CHCFCH3 (CH3)3CBr CH3CCI3 Br Br CI CI CI CI CI

Problem 3P For each of the following compounds, 1. give the IUPAC name. 2. give the common name (if possible). 3. classify the compound as a methyl, primary, secondary, or tertiary halide.

Kepone and chlordane are synthesized from hexachlorocyclopentadiene and other five- membered-ring compounds. Show how these two pesticides are composed of two five- membered rings. Equation Transcription: Text Transcription: CI CI CI CI CI CI

Problem 5P For each pair of compounds, predict which one has the higher molecular dipole moment, andexplain your reasoning. (a) ethyl chloride or ethyl iodide (b) 1-bromopropane or cyclopropane (c) cis-2,3-dibromobut-2-ene or trans-2,3-dibromobut-2-ene (d) cis-1,2-dichlorocyclobutane or trans-1,3-dichlorocyclobutane

When the following compound is treated with sodium methoxide in methanol, two elimination products are possible. Explain why the deuterated product predominates by about a \(7: 1\) ratio (refer to Problem 6-75). Equation Transcription: Text Transcription: 7:1 Br -OCH3 CH3OH 87% 13%

For each pair of compounds, predict which compound has the higher boiling point. Check Table 6-2 to see if your prediction was right, then explain why that compound has the higher boiling point. 1. isopropyl bromide and n-butyl bromide 2. isopropyl chloride and tert-butyl bromide 3. 1-bromobutane and 1-chlorobutane

Problem 7P When water is shaken with hexane, the two liquids separate into two phases. Which compoundis present in the top phase, and which is present in the bottom phase? When water is shakenwith chloroform, a similar two-phase system results. Again, which compound is present ineach phase? Explain the difference in the two experiments. What do you expect to happenwhen water is shaken with ethanol (CH3CH2OH)?

1. Propose a mechanism for the following reaction: 2. Use the bond-dissociation enthalpies given in Table 4-2 (page 143) to calculate the value of \(\Delta H^{\circ}\) for each step shown in your mechanism. (The \(B D E \text { for } C H_{2}=C H C H_{2}-B r\) is about \(280 \mathrm{~kJ} / \mathrm{mol}, or 67 \mathrm{kcal} / \mathrm{mol}\).) Calculate the overall value of \(\Delta H^{\circ}\) for the reaction. Are these values consistent with a rapid free-radical chain reaction? Equation Transcription: Text Transcription: H_{2} C=C H-C H_{3}+B r_{2} \stackrel{h v}{\rightarrow} H_{2} C=C H-C H_{2} B r+H B r \Delta H^{\circ} BDE for CH2=CHCH2-Br 280 kJ/mol, or 67 kcal/mol \Delta H^{\circ}

The light-initiated reaction of \(2,3 \text {-dimethylbut }-2-\text { ene }\) with \(\mathrm{N}-\text { bromosuccinimide }(\mathrm{NBS})\) gives two products: 1. Give a mechanism for this reaction, showing how the two products arise as a conse- quence of the resonance-stabilized intermediate. 2. The bromination of cyclohexene using NBS gives only one major product, as shown on page 227. Explain why there is no second product from an allylic shift. Equation Transcription: Text Transcription: 2,3-dimethylbut-2-ene N-bromosuccinimide (NBS) H3C CH3 H3C CH3 NBS,hv H3C H3C CH3 CH2-Br Br C CH3 CH3 C CH2 CH3

Classify each reaction as a substitution, elimination, or neither. Identify the leaving group in each reaction, and the nucleophile in substitutions.

Problem 12P Give the structures of the substitution products expected when 1-bromohexane reacts with (a) NaOCH2CH3 (b) KCN (c) NaOH

Show how free-radical halogenation might be used to synthesize the following compounds. In each case, explain why we expect to get a single major product. 1. 1-chloro-2,2-dimethylpropane (neopentyl chloride) 2. 2-bromo-2-methylbutane Equation Transcription: Text Transcription: Br-CH-CH_2CH_2CH_3 Br

(a) Under certain conditions, the reaction of 0.5 M 1-bromobutane with 1.0 M sodium methoxide forms 1-methoxybutane at a rate of 0.05 mol/L per second. What would be the rate if 0.1 M 1-bromobutane and 2.0 M \(\mathrm{NaOCH}_{3}\) were used? (b) Consider the reaction of 1-bromobutane with a large excess of ammonia (\(\mathrm{NH}_{3}\)). Draw the reactants, the transition state, and the products. Note that the initial product is the salt of an amine (\(\mathrm{RNH}_3^{\ +}\mathrm{\ Br}^-\)), which is deprotonated by the excess ammonia to give the amine. (c) Show another SN2 reaction using a different combination of an alkoxide and an alkyl bromide that also produces1-methoxybutane.

Predict the major products of the following substitutions. (a) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{Br}+\left(\mathrm{CH}_{3}\right)_{3} \mathrm{CO}^{-} \quad{ }^{+} \mathrm{K} \rightarrow\) b) \(\mathrm{HC} \equiv \mathrm{C}^{++} \mathrm{Na}+\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{Cl} \rightarrow\) sodium acetylide 1-chlorobutane (c) \(\left(\mathrm{CH}_{3}\right)_{2} \mathrm{CHCH}_{2} \mathrm{Br}+\text { excess } \mathrm{NH}_{3} \rightarrow\) (d) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{I}+\mathrm{NaCN} \rightarrow\) (e) \(1-\text { chloropentane }+\mathrm{Nal} \rightarrow\) (f) \(1-\text { chloropentane }+\mathrm{KF} \frac{18-\mathrm{crown}-6}{\mathrm{CH}_{3} \mathrm{CN}}\) Equation Transcription: Text Transcription: CH_3CH_2Br + (CH_3)_3CO- +K \rightarrow HCC-+Na + CH_3CH_2CH_2CH_2Cl \rightarrow (CH_3)_2CHCH_2Br+excess NH_3 \rightarrow CH_3CH_2CH_2I+NaCN \rightarrow 1-chloropentane+Nal \rightarrow 1-chloropentane+KF18-crown-6CH_3CN

Show how you might use \(S_{N} 2 \) reactions to convert \(1 \text { - chlorobutane }\) into the following compounds. (a) \(\text { butan }-1-\text { ol }\) (b) \(1 \text {-fluorobutane }\) (c) \(1-\text { iodobutane }\) (d) \(\mathrm{CH}_{3}-\left(\mathrm{CH}_{2}\right)_{3}-\mathrm{CN}\) (e) \(\mathrm{CH}_{3}-\left(\mathrm{CH}_{2}\right)_{3}-\mathrm{C} \equiv \mathrm{CH}\) (f) \(\mathrm{CH}_{3} \mathrm{CH}_{2}-\mathrm{O}-\left(\mathrm{CH}_{2}\right)_{3}-\mathrm{CH}_{3}\) (g) \(\mathrm{CH}_{3}-\left(\mathrm{CH}_{2}\right)_{3}-\mathrm{NH}_{2}\) Equation Transcription: Text Transcription: S_N2 1-chlorobutane butan-1-ol 1-flourobutane 1-iodobutane CH_3-(CH_2)_3-CN CH_3-(CH_2)_3-CCH CH_3CH_2-O-(CH_2)_3-CH_3 CH_3-(CH_2)_3-NH_2

For each pair, predict the stronger nucleophile in the \(\mathrm{S}_{\mathrm{N}} 2\) reaction (using an alcohol as the solvent). Explain your prediction. (a) \(left(\mathrm{CH}_{3} \mathrm{CH}_{2}\right)_{3} \mathrm{~N} \text { or }\left(\mathrm{CH}_{3} \mathrm{CH}_{2}\right)_{2} \mathrm{NH}\) (b) \(\left(\mathrm{CH}_{3}\right)_{2} \mathrm{O} \text { or }\left(\mathrm{CH}_{3}\right)_{2} \mathrm{~S}\) (c) \(\mathrm{NH}_{3} \text { or } \mathrm{PH}_{3}\) (d) \(\mathrm{CH}_{3} \mathrm{~S}^{-} \text {or } \mathrm{H}_{2} \mathrm{~S}\) (e) \(\left(\mathrm{CH}_{3}\right)_{3} \mathrm{N or}\left(\mathrm{CH}_{3}\right)_{2} \mathrm{O}\) (f) \(\mathrm{CH}_{3} \mathrm{COO}^{-} \text {or } \mathrm{CF}_{3} \mathrm{COO}^{-}\) (g) \(\left(\mathrm{CH}_{3}\right)_{2} \mathrm{CHO}^{-} \text {or } \mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{O}^{-}\) (h) \(\mathrm{I}^{-} \text {or } \mathrm{Cl}^{-}\) Problem-solving Hint Steric hindrance (bulkiness) hinders nucleophilicity \(\left(\mathrm{S}_{\mathrm{N}} 2\right)\) more than it hinders basicity. Equation Transcription: Text Transcription: S_N2 (CH_3CH_2)_3 N or (CH_3CH_2)_2NH (CH_3)_2O or (CH_3)_2S NH_3 or PH_3 CH_3S- or H_2S (CH_3)_3N or (CH_3)_2O CH_3COO- or CF_3COO- (CH_3)_2CHO- or CH_3CH_2CH_2O- I- or Cl- (S_N2)

Problem 17P When diethyl ether (CH3CH2OCH2CH3) is treated with concentrated HBr, the initial products are CH3CH2Br and CH3CH2OH. Propose a mechanism to account for this reaction.

Rank the following compounds in decreasing order of their reactivity toward the \(S_{N} 2\) reaction with sodium ethoxide \(\left(\mathrm{Na}^{+}-\mathrm{OCH}_{2} \mathrm{CH}_{3}\right)\) in ethanol. methyl chloride tert-butyl iodide neopentyl bromide isopropyl bromide methyl iodide ethyl chloride Problem-solving Hint Do not write \(S_{N} 2\) reactions occurring on tertiary alkyl halides. Equation Transcription: Text Transcription: S_N2 (Na+-OCH_2CH_3) SN2

For each pair of compounds, state which compound is the better \(\mathrm{S}_{\mathrm{N}} 2\) substrate. (a) 2-methyl-1-iodopropane or tert-butyl iodide (b) cyclohexyl bromide or 1-bromo-1-methylcyclohexane (c) 2-bromobutane or isopropyl bromide (d) 1 -chloro- 2,2 -dimethylbutane or 2 -chlorobutane (e) 1-iodobutane or 2-iodopropane

Draw a perspective structure or a Fischer projection for the products of the following \(S_{N} 2\) reactions. (a) \(\text { trans }-1-\text { bromo }-3-\text { methylcyclopentane }+K O H\) (b) \((R)-2-\text { bromopentane }+K C N\) Equation Transcription: Text Transcription: S_N2 trans-1-bromo-3-methylcyclopentane+KOH (R)-2-bromopentane+KCN

Under appropriate conditions, \((S)-1\) -bromo- 1 -fluoroethane reacts with sodium methoxide to give \((R) and (S)\) are just names. Don't pure \((S)-1\) -fluoro-1-methoxyethane. rely on names to determine the stereochemistry of a reaction \(\mathrm{CH}_{3} \mathrm{CHBr} \mathrm{F}+\mathrm{NaOCH}_{3} \rightarrow \mathrm{CH}_{3} \mathrm{CHF} \mathrm{OCH}_{3}+\mathrm{NaBr}\) \((S)\) \((S)\) (a) Why is bromide rather than fluoride replaced? (b) Draw perspective structures (as shown on the previous page for 2 -bromobutane) for the starting material, the transition state, and the product. (c) Does the product show retention or inversion of configuration? (d) Is this result consistent with reaction by the \(S_{N} 2\) mechanism? Problem-solving Hint \((R) and (S)\) are just names. Don’t rely on names to determine the stereochemistry of a reaction. Equation Transcription: Text Transcription: (S)-1 (R) and (S) (S)-1 CH_3CHBrF+NaOCH3_CH_3CHFOCH_3+NaBr (S) (S) S_N2 (R) and (S)

Problem 22P Propose an SN1 mechanism for the solvolysis of 3-bromo-2,3-dimethylpentane in ethanol.

Choose the member of each pair that will react faster by the \(S_N1\) mechanism. (a) 1-bromopropane or 2-bromopropane (b) 2-bromo-2-methylbutane or 2-bromo-3-methylbutane (c) n-propyl bromide or allyl bromide (d) 1-bromo-2,2-dimethylpropane or 2-bromopropane (e) 2-iodo-2-methylbutane or tert-butyl chloride (f) 2-bromo-2-methylbutane or ethyl iodide

3-Bromocyclohexene is a secondary halide, and benzyl bromide is a primary halide. Both halides undergo \(S_{N} 1\) substitution about as fast as most tertiary halides. Use resonance structures to explain this enhanced reactivity. Equation Transcription: Text Transcription: S_N1 Br CH2Br

Problem 25P Give the SN1 mechanism for the formation of 2-ethoxy-3-methylbutane, the unrearrangedproduct in this reaction.

Propose a mechanism involving a hydride shift or an alkyl shift for each solvolysis reaction. Explain how each rearrangement forms a more stable intermediate.

Problem 27P For each reaction, give the expected substitution product, and predict whether the mechanismwill be predominantly first order (SN1) or second order (SN2). (a) 2-chloro-2-methylbutane + CH3COOH (b) isobutyl bromide + sodium methoxide (c) 1-iodo-1-methylcyclohexane + ethanol (d) cyclohexyl bromide + methanol (e) cyclohexyl bromide + sodium ethoxide

Under certain conditions, when \((R)-2\) -bromobutane is heated with water, the \(S_{N} 1\) substitution proceeds twice as fast as the \(S_{N} 2\). Calculate the e.e. and the specific rotation expected for the product. The specific rotation of \((R)\) -butan-2-ol is \(-13.5^{\circ}\). Assume that the \(S_{N} 1\) gives equal amounts of the two enantiomers. Equation Transcription: Text Transcription: (R)-2 S_N1 S_N2 (R) -13.5° S_N1

A reluctant first-order substrate can be forced to ionize hy adding some silver nitrate (one of the few soluble silver salts) to the reaction. Silver ion reacts with the halogen to form a silver halide (a highly exothermic reaction), generating the cation of the alkyl group. \(R-X+A g^{+}>R^{+}+A g X \downarrow\) Give mechanisms for the following silver-promoted rearrangements. Equation Transcription: Text Transcription: R-X+A g^{+}>R^{+}+A g X \downarrow CH_3 CH_3 CH_2 CH_3 AgNO_3,H_2O CH_3 CH_3 CH_3 CH_2 OH CH_2I AgNO_3,H_2O/CH_3CH_2OH

Problem 30P SN1 substitution and E1 elimination frequently compete in the same reaction. (a) Propose a mechanism and predict the products for the solvolysis of 1-bromo-1- methyl-cyclopentane in ethanol. (b) Compare the function of the solvent (ethanol) in the E1 and SN1 reactions.

Problem 31P The solvolysis of 2-bromo-3-methylbutane potentially can give several products, includingboth E1 and SN1 products from both the unrearranged carbocation and the rearranged carbocation. Mechanisms 6-6 (page 253) and 6-9 (previous page) show the products from therearranged carbocation. Summarize all the possible products, showing which carbocation theycome from and whether they are the products of E1 or SN1 reactions.

Finish Partially Solved Problem 6-1 by showing how the rearranged carbocations give the four products shown in the problem. Be careful when using curved arrows to show deprotonation and or nucleophilic attack by the solvent. The curved arrows always show movement of electrons, not movement of protons or other species.

Give the substitution and elimination products you would expect from the following reactions. (a) 3-bromo-3-ethylpentane heated in methanol (b) 1-iodo-1-methylcyclopentane heated in ethanol (c) 3-bromo-2,2-dimethylbutane heated in ethanol (d) 1-iodo-2-methylcyclohexane + silver nitrate in water (see Problem 6-29)

When 1-bromo-1-methylcyclohexane is heated in ethanol for an extended period of time, three products result: one ether and two alkenes. Predict the products of this reaction, and propose a mechanism for their formation. Predict which of the two alkenes is the major elimination product.

Problem 36P Under second-order conditions (strong base nucleophile), SN2and E2 reactions may occur simultaneously and compete with each other. Show what products might be expected from the reaction of 2-bromo-3-methylbutane (a moderately hindered 2° alkyl halide) with sodium ethoxide.

Problem 36P 1. Predict the elimination products of the following reactions. When two alkenes are possible, predict which one will be the major product. Explain your answers, showing the degree of substitution of each double bond in the products. 2. Which of these reactions are likely to produce both elimination and substitutionproducts? (a) 2-bromopentane + NaOCH3 (b) 3-bromo-3-methylpentane + NaOMe (Me = methyl, CH3) (c) 2-bromo-3-ethylpentane + NaOH (d) cis-1-bromo-2-methylcyclohexane + NaOEt (Et = ethyl, CH2CH3)

When the first compound shown here is treated with sodium methoxide, the only elimination product is the trans isomer. The second diastereomer (blue) gives only the cis product. Use your models and careful drawings of the transition states to explain these results.

Problem 39P Give the structures of the products expected from the indicated mechanisms in the preceding examples.

Predict the products and mechanisms of the following reactions. When more than one product or mechanism is possible, explain which are most likely. (a) 1-bromohexane sodium ethoxide in ethanol (b) 2 -chlorohexane + \(\mathrm{NaOCH}_{3}\) in methanol (c) 2 -chloro-2-methylbutane + \(\mathrm{NaOCH}_{2} \mathrm{CH}_{3}\) in ethanol (d) 2 -chloro-2-methylbutane heated in ethanol (e) isobutyl iodide + \(\mathrm{KOH}\) in ethanol/water (f) isobutyl chloride + \(\mathrm{AgNO}_{3}\) in ethanol in ethanol/water (g) 1-bromo-1-methylcyclopentane + \(\mathrm{NaOEt}\) in ethanol (h) 1-bromo-1-methylcyclopentane heated in methanol Equation Transcription: Text Transcription: NaOCH_3 NaOCH_2CH_3 KOH AgNO_3 NaOEt

Show how you would convert (in one or two steps) 1-phenylpropane to the three products shown below. In each case, explain what unwanted reactions might produce undesirable impurities in the product. Equation Transcription: Text Transcription: Br OCH_3

Problem 42SP Draw the structures of the following compounds. (a) sec-butyl chloride (b) isobutyl bromide (c) 1,2-dibromo-3-methylpentane (d) 2,2,2-trichloroethanol (e) trans-1-chloro-2-methylcyclohexane (f) methylene chloride (g) chloroform (h) 1-chloro-1-isopropylcyclopentane (i) tert-pentyl iodide

Give systematic \((I U P A C)\) names for the following compounds. Equation Transcription: Text Transcription: (IUPAC) Br Cl CH_3 Cl Cl CH_2CH_2Br Cl Cl CH_2I Cl CH_3 Cl

Predict the compound in each pair that will undergo the \(S_{N} 2\) reaction faster. Equation Transcription: Text Transcription: S_N2 Cl CH_2Cl Cl Br Br

Predict the compound in each pair that will undergo solvolysis (in aqueous ethanol) more rapidly. Equation Transcription: Text Transcription: (CH3CH2)2CH-Cl or (CH3)3C-Cl Cl or Cl Br or CH2Br Br or Br Br or Br

Show how each compound might be synthesized by the \(S_{N} 2\) displacement of an alkyl halide. Equation Transcription: Text Transcription: S_N2 CH_2OH SCH_2CH_3 CH_2NH_2 H_2C=CH-CH_2CN H-CC-CH_2CH_2CH_3

(a) Give two syntheses for \(\left(\mathrm{CH}_{3}\right)_{2} \mathrm{CH}-\mathrm{O}-\mathrm{CH}_{2} \mathrm{CH}_{3}\), and explain which synthesis is better. (b) A student wanted to synthesize methyl tert-butyl ether, \(\mathrm{CH}_{3}-\mathrm{O}-\mathrm{C}\left(\mathrm{CH}_{3}\right)_{3}\). He attempted the synthesis by adding sodium methoxide \(\left(\mathrm{CH}_{3} \mathrm{ONa}\right)\) to tert-butyl chloride, but he obtained none of the desired product. Show what product is formed in this reaction, and give a better synthesis for methyl tert-butyl ether. Equation Transcription: Text Transcription: (CH_3)_2CH-O-CH_2CH_3 CH_3-O-C(CH_3)_3 (CH_3ONa)

When ethyl bromide is added to potassium tert-butoxide, the product is ethyl tert-butyl ether. \(\mathrm{CH}_{3} \mathrm{CH}_{2}-\mathrm{Br}+\left(\mathrm{CH}_{3}\right)_{3} \mathrm{C}-\mathrm{O}^{-+} \mathrm{K} \rightarrow\left(\mathrm{CH}_{3}\right)_{3} \mathrm{C}-\mathrm{O}-\mathrm{CH}_{2} \mathrm{CH}_{3}\) ethyl bromide potassium tert-butoxide ethyl tert-butyl ether (a) What happens to the reaction rate if the concentration of ethyl bromide is doubled? (b) What happens to the rate if the concentration of potassium tert-butoxide is tripled and the concentration of ethyl bromide is doubled? (c) What happens to the rate if the temperature is raised? Equation Transcription: Text Transcription: CH_3CH_2-Br + (CH_3)_3C-O^-+K \rightarrow (CH_3)_3C-O-CH_2CH_3

Problem 49SP When tert-butyl bromide is heated with an equal amount of ethanol in an inert solvent, one of the products is ethyl tert-butyl ether. (a) What happens to the reaction rate if the concentration of ethanol is doubled? (b) What happens to the rate if the concentration of tert-butyl bromide is tripled and the concentration of ethanol is doubled? (c) What happens to the rate if the temperature is raised?

Problem 50SP Chlorocyclohexane reacts with sodium cyanide (NaCN) in ethanol to give cyanocyclohexane. The rate of formation of cyanocyclohexane increases when a small amount of sodium iodide is added to the solution. Explain this acceleration in the rate.

Give the solvolysis products expected when each compound is heated in ethanol. Equation Transcription: Text Transcription: Br Cl CH_3 Br Br

Allylic halides have the structure (a) Show how the first-order ionization of an allylic halide leads to a resonance-stabilized cation. (b) Draw the resonance structures of the allylic cations formed by ionization of the following halides. (c) Show the products expected from \(S_{N} 1\) solvolysis of these halides in ethanol Equation Transcription: Text Transcription: C=C-C-X S_N1 Br CH2Br Br Br

List the following carbocations in decreasing order of their stability. Equation Transcription: Text Transcription: CH_3 +CH_2 +CH_2 CH_3 CH_3

Two of the carbocations in Problem 6-53 are prone to rearrangement. Show how they might rearrange to more stable carbocations.

Draw perspective structures or Fischer projections for the substitution products of the following reactions.

Predict the products of the following \(S_{N} 2\) reactions. Equation Transcription: Text Transcription: S_N2

When \((\pm)-2,3\) -dibromobutane reacts with potassium hydroxide, some of the products are \((2 S, 3 R)-3\) -bromobutan-2-ol and its enantiomer and trans-2-bromobut-2-ene. Give mechanisms to account for these products. Equation Transcription: Text Transcription: ( \pm)-2,3 (2S, 3R)-3 CH_3 OH Br CH_3 CH_3 HO CH_3 Br H_3C Br CH_3

A solution of pure \((S)-2\)-iodobutane \(\left([\alpha]=+15.90^{\circ}\right)\) in acetone is allowed to react with radioactive iodide,\({ }^{131} \Gamma\), until \(1.0 \% \) of the iodobutane contains radioactive iodine. The specific rotation of this recovered iodobutane is found to be \(+15.58 \circ\) (a) Determine the percentages of \((R)-\text { and }(S)-2\) -iodobutane in the product mixture. (b) What does this result suggest about the mechanism of the reaction of 2 -iodobutane with iodide ion? Equation Transcription: Text Transcription: (S)-2 \left([\alpha]=+15.90^{\circ}\right) { }^{131} \Gamma 1.0% +15.58° (R)- and (S)-2

Problem 59SP (a) Optically active 2-bromobutane undergoes racemization on treatment with a solution of KBr. Give a mechanism for this racemization. (b) In contrast, optically active butan-2-ol does not racemize on treatment with a solution of KOH. Explain why a reaction like that in part (a) does not occur. (c) Optically active butan-2-ol racemizes in dilute acid. Propose a mechanism for this racemization.

Predict the products of E1 elimination of the following compounds. Label the major products. Equation Transcription: Text Transcription: CH_3 Br CH_3 Br (CH_3)_3C-CH-Br-CH_3

Problem 61SP Propose mechanisms and draw reaction-energy diagrams for the following reactions. Pay particular attention to the structures of any transition states and intermediates. Compare the reaction-energy diagrams for the two reactions, and explain the differences. (a) 2-Bromo-2-methylbutane reacts with sodium methoxide in methanol to give 2-methylbut-2-ene (among other products). (b) 2-Bromo-2-methylbutane reacts in boiling methanol to give 2-methylbut-2-ene (among other products).

Protonation converts the hydroxyl group of an alcohol to a good leaving group. Suggest a mechanism for each reaction. Equation Transcription: Text Transcription: OH (E1) \rightarrow H2SO4, heat+ H2O OH (SN2 or SN1) \rightarrow HBr, heat - Br + H2O

Give a mechanism to explain the two products formed in the following reaction. Equation Transcription: Text Transcription: CH_3 CH_3 NBS, hv Br CH_3 CH_3 Br CH_3 CH_3

Predict the major product of the following reaction, and give a mechanism to support your prediction. Equation Transcription: Text Transcription: CH_2CH_3 NBS, hv

Problem 65SP Because the SN1 reaction goes through a flat carbocation, we might expect an optically active starting material to give a completely racemized product. In most cases, however, SN1 reactions actually give more of the inversion product. In general, as the stability of the carbocation increases, the excess inversion product decreases. Extremely stable carbocations give completely racemic products. Explain these observations.

When 1-bromo-2-methylcyclohexane undergoes solvolysis in methanol, five major products are formed. Give mechanisms to account for these products. Equation Transcription: Text Transcription: Br CH_3 CH_3OH OCH CH_3 OCH_3 CH_3 CH_3 CH_2 CH_3

Problem 67SP Triethyloxonium tetrafluoroborate, (CH3CH2)3O+BF4 -, is a solid with melting point 91–92 °C. Show how this reagent can transfer an ethyl group to a nucleophile (Nuc:-)in an SN2 reaction. What is the leaving group? Why might this reagent be preferred to an ethyl halide? (Consult Table 6-2.)

Furfuryl chloride can undergo substitution by both \(S_{N} 2 \text { and } S_{N} 1\) mechanisms. Since it is a \(1^{\circ}\) alkyl halide, we expect \(S_{N} 2\) but not \(S_{N} 1\) reactions. Draw a mechanism for the \(S_{N} 1\) reaction shown below, with careful attention to the structure of the intermediate. How can this primary halide undergo \(S_{N} 1\) reactions? Why is there no competition with \(E 2 \text { or } E 1\) mechanisms? Equation Transcription: Text Transcription: SN2 and SN1 1° SN2 SN1 SN1 SN1 E2 or E1 NaOCHO NaCl

The reaction of an amine with an alkyl halide gives an ammonium salt. \(R_{3} N:+R^{\prime}-X \rightarrow R_{3} N-R^{\prime} X\) amine alkyl halide ammonium salt The rate of this \(S_{N} 2\) reaction is sensitive to the polarity of the solvent. Draw an energy diagram for this reaction in a nonpolar solvent and another in a polar solvent. Consider the nature of the transition state, and explain why this reaction should be sensitive to the polarity of the solvent. Predict whether it will be faster or slower in a more polar solvent. Equation Transcription: Text Transcription: R_3 N:+R^X \rightarrow R_3 N-R^ X S_N2

Problem 73SP Pure (S)-2-bromo-2-fluorobutane reacts with methoxide ion in methanol to give a mixture of (S)-2-fluoro-2-methoxybutane and three fluoroalkenes. (a) Use mechanisms to show which three fluoroalkenes are formed. (b) Propose a mechanism to show how (S)-2-bromo-2-fluorobutane reacts to give (S)-2-fluoro-2 methoxybutane. Has this reaction gone with retention or inversion of configuration?

Deuterium (D) is the isotope of hydrogen of mass number 2 , with a proton and a neutron in its nucleus. The chemistry of deuterium is nearly identical to the chemistry of hydrogen, except that the \(C-D\) bond is slightly \((5.0 \mathrm{~kJ} / \mathrm{mol}$, or $1.2 \mathrm{kcal} / \mathrm{mol})\) stronger than the bond. Reaction rates tend to be slower if a \(C-D\)bond (as opposed to a \(C-H\) bond) is broken in a rate-limiting step. This effect on the rate is called a kinetic isotope effect. (Review Problem 4-56.) (a) Propose a mechanism to explain each product in the following reaction. (b) When the following deuterated compound reacts under the same conditions, the rate of formation of the substitution product is unchanged, while the rate of formation of the elimination product is slowed by a factor of Explain why the elimination rate is slower, but the substitution rate is unchanged. (c) A similar reaction takes place on heating the alkyl halide in an acetone/water mixture. Give a mechanism for the formation of each product under these conditions, and predict how the rate of formation of each product will change when the deuterated halide reacts. Explain your prediction. Equation Transcription: Text Transcription: C-D (5.0 kJ/mol, or 1.2kcal/mol) C-H C-D C-H

Solvolysis of bromomethylcyclopentane in methanol gives a complex product mixture of the following five compounds. Propose mechanisms to account for these products.

Propose mechanisms to account for the observed products in the following reactions. In some cases more products are formed, but you only need to account for the ones shown here.

(a) Design an alkyl halide that will give only 2,4 -diphenylpent-2-ene upon treatment with potassium tert-butoxide (a bulky base that promotes E2 elimination). (b) What stereochemistry is required in your alkyl halide so that only the following stereoisomer of the product is formed? Equation Transcription: Text Transcription: Ph H_3C C=C CH(Ph)CH_3

Each of the two carbocations in Solved Problem 6-2 can also react with ethanol to give a sub- stitution product. Give the structures of the two substitution products formed in this reaction. Eliminations can also take place under second-order conditions with a strong base present. As an example, consider the reaction of tert-butyl bromide with methoxide ion in methanol. This is a second-order reaction because methoxide ion is a strong base as well as a strong nucleophile. It attacks the alkyl halide faster than the halide can ionize to give a first-order reaction. No substitution product (methyl tert-butyl ether) is observed, however. The \(\mathrm{S}_{\mathrm{N}} 2\) mechanism is blocked because the tertiary alkyl halide is too hindered. The observed product is 2-methylpropene, resulting from elimination of \(\text {HBr}\) and formation of a double bond. \(\text { Rate }=k_{r}\left[\left(\mathrm{CH}_{3}\right)_{3} \mathrm{C}-\mathrm{Br}\right]\left[^{-} \mathrm{OCH}_{3}\right]\) The rate of this elimination is proportional to the concentrations of both the alkyl halide and the base, giving a second-order rate equation. This is a bimolecular process, with both the base and the alkyl halide participating in the transition state, so this mechanism is abbreviated \(\text {E2}\) for Elimination, bimolecular. \(\mathrm{E} 2 \text { rate }=k_{r}[\mathrm{RX}]\left[\mathrm{B}:^{-}\right]\) In the \(\text {E2}\) reaction just shown, methoxide reacts as a base rather than as a nucleophile. Most strong nucleophiles are also strong bases, and elimination commonly results when a strong base nucleophile is used with a poor \(\mathrm{S}_{\mathrm{N}} 2\) substrate such as a \(3^{\circ}\) or hindered \(2^{\circ}\) alkyl halide. Instead of attacking the back side of the hindered electrophilic carbon, methoxide abstracts a proton from one of the methyl groups. This reaction takes place in one step, with bromide leaving as the base abstracts a proton. In the general mechanism of the \(\text {E2}\) reaction, a strong base abstracts a proton on a carbon atom adjacent to the one with the leaving group. As the base abstracts a proton, a double bond forms and the leaving group leaves. Like the \(\mathrm{S}_{\mathrm{N}} 2\) reaction, the \(\text {E2}\) is a concerted reaction in which bonds break and new bonds form at the same time, in a single step. Reactivity of the Substrate in the \(\text {E2}\) The order of reactivity of alkyl halides toward E2 dehydrohalogenation is found to be \(3^{\circ}>2^{\circ}>1^{\circ}\) Equation Transcription: Text Transcription: S_{N}2 HBr S_{N}2 CH_{3}O E2 CH_{3} CH_{3} Br E2 CH_{3}-O-H CH_{3} C-C CH_{3} Rate =k_{r}[(CH_{3})_{3}C-Br][^{-}OCH_{3}] E2 E2 rate=k_{r}[RX] [B:^{-}] E2 S_{N}2 3^o 2^o E2 S_{N}2 E2 E2 3^o>2^o>1^o