The following reaction takes place under second-order conditions (strong nucleophile)

Classify each compound as an alkyl halide, a vinyl halide, or an aryl halide. (a) CH3CHCFCH3 (b) (CH3)3CBr (c) CH3CCl3 (d) Br bromocyclohexane Br 1-bromocyclohexene (e) (f) Cl a PCB (polychlorinated biphenyl) Cl Cl Cl Cl

Give the structures of the following compounds. (a) methylene iodide (b) carbon tetrabromide (c) 3-bromo-2-methylpentane (d) iodoform (e) 2-bromo-3-ethyl-2-methylhexane (f) isobutyl bromide (g) cis-1-fluoro-3-(fluoromethyl)cyclohexane (h) tert-butyl chloride

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, aldrin, and chlordane are synthesized from hexachlorocyclopentadiene and other five-membered-ring compounds. Show how these three pesticides are composed of two five-membered rings. Cl Cl Cl Cl Cl Cl hexachlorocyclopentadiene

For each pair of compounds, predict which one has the higher molecular dipole moment, and explain 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

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. (a) isopropyl bromide and n-butyl bromide (b) isopropyl chloride and tert-butyl bromide (c) 1-bromobutane and 1-chlorobutane

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

(a) Propose a mechanism for the following reaction: H2C CH CH3 Br + 2 H2C CH CH2Br HBr + h (b) Use the bond-dissociation enthalpies given in Table 4-2 (page 167) to calculate the value of H for each step shown in your mechanism. (The BDE for CH2CHCH2Br is about 280 kJ>mol, or 67 kcal>mol.) Calculate the overall value of H for the reaction. Are these values consistent with a rapid free-radical chain reaction?

The light-initiated reaction of 2,3-dimethylbut-2-ene with N-bromosuccinimide (NBS) gives two products: H3C CH3 C C H3C CH3 2,3-dimethylbut-2-ene H3C CH2 C C H3C CH3 + Br Br C CH3 CH3 CH2 C CH3 NBS, h (a) Give a mechanism for this reaction, showing how the two products arise as a consequence of the resonance-stabilized intermediate. (b) The bromination of cyclohexene using NBS gives only one major product, as shown on the previous page. Explain why there is no second product from an allylic shift.

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. (a) 1-chloro-2,2-dimethylpropane (neopentyl chloride) (b) 2-bromo-2-methylbutane CH CH2CH2CH3 Br (c) 1-bromo-1-phenylbutane (d) Br

Classify each reaction as a substitution, an elimination, or neither. Identify the leaving group in each reaction, and the nucleophile in substitutions. (a) H Br H OCH3 + NaBr

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

(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 \(NaOCH_3\) were used? (b) Consider the reaction of 1-bromobutane with a large excess of ammonia (\(NH_3\)). Draw the reactants, the transition state, and the products. Note that the initial product is the salt of an amine (\(RNH_3^+Br^-\)), which is deprotonated by the excess ammonia to give the amine. (c) Show another \(S_N2\) reaction using a different combination of an alkoxide and an alkyl bromide that also produces 1-methoxybutane.

Predict the major products of the following substitutions. (a) CH3CH2Br + (CH3)3CO- K+ ethyl bromide potassium tert@butoxide (b) HCC:- Na+ + CH3CH2CH2CH2Cl sodium acetylide 1@chlorobutane

Show how you might use SN2 reactions to convert 1-chlorobutane into the following compounds. (a) butan-1-ol (b) 1-fluorobutane (c) 1-iodobutane (d) CH3(CH2)3CN (e) CH3(CH2)3CCH (f) CH3CH2O(CH2)3CH3 (g) CH3(CH2)3NH2

For each pair, predict the stronger nucleophile in the SN2 reaction (using an alcohol as the solvent). Explain your prediction. (a) (CH3CH2)3N or (CH3CH2)2NH (b) (CH3)2O or (CH3)2S (c) NH3 or PH3 (d) CH3S- or H2S (e) (CH3)3N or (CH3)2O (f) CH3COO- or CF3COO(g) (CH3)2CHO- or CH3CH2CH2O- (h) I - or Cl

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 SN2 reaction with sodium ethoxide (Na+ -OCH2CH3) in ethanol. methyl chloride tert-butyl iodide neopentyl bromide isopropyl bromide methyl iodide ethyl chloride

Rank the following compounds in decreasing order of their reactivity toward the SN2 reaction with sodium ethoxide (Na+ -OCH2CH3) in ethanol. methyl chloride tert-butyl iodide neopentyl bromide isopropyl bromide methyl iodide ethyl chloride

Draw a perspective structure or a Fischer projection for the products of the following SN2 reactions. (a) trans@1@bromo@3@methylcyclopentane + KOH (b) (R)@2@bromopentane + KCN CH2CH3 CH3 CH3 H H Br (c) + NaI acetone (d) C F CH3 H Br + NaSH CH3 H Br (e) + NaOCH3 CH3OH CH2CH2CH3 (f) C D Cl H + NH3 excess

Under appropriate conditions, (S)-1-bromo-1-fluoroethane reacts with sodium methoxide to give pure (S)-1-fluoro-1-methoxyethane. CH3CHBrF + NaOCH3 CH3CHFOCH3 + 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 SN2 mechanism?

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 SN1 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 SN1 substitution about as fast as most tertiary halides. Use resonance structures to explain this enhanced reactivity. Br CH2Br 3-bromocyclohexene benzyl bromide

Give the SN1 mechanism for the formation of 2-ethoxy-3-methylbutane, the unrearranged product 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.

For each reaction, give the expected substitution product, and predict whether the mechanism will 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 \(S_N1\) substitution proceeds twice as fast as the \(S_N2\). 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 \(S_N1\) gives equal amounts of the two enantiomers.

A reluctant first-order substrate can be forced to ionize by 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. RX + Ag+ R+ + AgX T Give mechanisms for the following silver-promoted rearrangements. C I CH3 CH3 CH3 CH2 CH3 CH3 C CH2 CH3 OH AgNO3, H2O (a) CH2I OH AgNO3, H2O/CH3CH2OH

Correctly name alkyl halides; summarize their physical properties; and identify them as \(1^{\circ}\), \(2^{\circ}\), or \(3^{\circ}\). (Problems 6-31, 32, and 47)

Show how free-radical halogenation might be used for the synthesis of some alkyl halides, especially for making allylic and benzylic alkyl halides. (Problems 6-30, 46, 51, 57, 58, and 59)

Predict the products of \(\mathrm{S}_{\mathrm{N}} 1\) and \(\mathrm{S}_{\mathrm{N}} 2\) reactions, including stereochemistry.

Draw the mechanisms and reaction-energy diagrams of SN1 and SN2 reactions.

Predict and explain the relative stabilities and rearrangements of cations involved in first-order reactions.

Predict which substitutions will be faster, based on differences in substrate, nucleophile, leaving group, and solvent. (Problems 6-33, 34, 36, 37, 38, and 39)

Given a set of reaction conditions, predict whether the reaction will be unimolecular (first-order) or bimolecular (second-order), and predict which product(s) are most likely. (Problems 6-37, 38, 54, and 56)

Show how substitutions of alkyl halides might be used to synthesize other types of compounds. (Problems 6-30, 35, 36, 39, 40, 45, 46, 53, and 54)

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. 1-phenylpropane 1-bromo-1-phenylpropane Br (a) 1-methoxy-1-phenylpropane (b) OCH3 2-phenylbutanenitrile

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 (h) tert-pentyl iodide

Give systematic (IUPAC) names for the following compounds. (a) (a) Br (b) Cl CH3 (b) (c) F Cl Cl (c) (d) CH2CH2Br F (d) (e) Cl CH2I (e) Cl (f) Cl CH3 Cl H

Predict the compound in each pair that will undergo the SN2 reaction faster. (a) Cl or Cl (a) (b) Cl or I (b) (c) Cl or (c) Cl (d) Br or Br (d) (e) Cl or CH2Cl (e) (f) Br or Br

Predict the compound in each pair that will undergo solvolysis (in aqueous ethanol) more rapidly. (a) (CH3CH2)2CHCl or (CH3)3CCl (b) Cl Cl (b) or (c) Br or (c) CH2Br (d) Cl or (d) I (e) Br or (e) Br (f) Br or Br

Show how each compound might be synthesized by the SN2 displacement of an alkyl halide. (a) CH2OH (a) (b) SCH2CH3 (b) (c) O (c) (d) CH2NH2 (d) (e) H2CCHCH2CN (f) HCCCH2CH2CH3

Give two syntheses for (CH3)2CHOCH2CH3, and explain which synthesis is better

When ethyl bromide is added to potassium tert-butoxide, the product is ethyl tert-butyl ether. CH3CH2Br + (CH3)3CO- K+ (CH3)3COCH2CH3 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?

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?

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 substitution products expected from solvolysis of each compound by heating in ethanol.

Allylic halides have the structure C C C X (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 SN1 solvolysis of these halides in ethanol. (i) (ii) CH2Br Br (iii) Br (iv)

List the following carbocations in decreasing order of their stability. CH3 CH2 CH2 CH3 CH3

Two of the carbocations in Problem 6-42 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. acetone water/acetone EtOH, heat CH3 Br CH2CH

Predict the products of the following SN2 reactions. (a) CH3CH2ONa + CH3CH2Cl (b) CH2CH2Br + NaCN (b) (c) S Na CH3CH2Br + + (c) (d) CH3(CH2)8CH2Cl + Na+ -:CCH (e) N CH3 + I (e) (f) (CH3)3CCH2CH2Br + excess NH3 (g) OH Cl + NaOH (g) (h) Br CH3 NaOH CH3OH

Using cyclohexane as one of your starting materials, show how you would synthesize the following compounds.

Strawberry growers have used large quantities of methyl bromide (b.p. \(4^{\circ}C\)) to sterilize the soil before planting their crops. Like some of the freons, methyl bromide can diffuse up into the stratosphere, where it damages the protective ozone layer. Agricultural chemists have suggested using methyl iodide (b.p. \(43^{\circ}C\)) as a replacement for methyl bromide. Why is methyl iodide likely to be more toxic to agricultural pests (and people) than methyl bromide? Why is methyl iodide less likely to reach the stratosphere than methyl bromide?

A solution of pure (S)-2-iodobutane ([a] = +15.90) in acetone is allowed to react with radioactive iodide, 131I -, until 1.0% of the iodobutane contains radioactive iodine. The specific rotation of this recovered iodobutane is found to be +15.58. (a) Determine the percentages of (R)- 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?

(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.

Give a mechanism to explain the two products formed in the following reaction.

Predict the major product of the following reaction, and give a mechanism to support your prediction.

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.

Triethyloxonium tetrafluoroborate, (CH3CH2)3O+ BF4 , is a solid with melting point 9192 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 using an ethyl halide? (Consult Table 6-2.)

Furfuryl chloride can undergo substitution by both \(S_N2\) and \(S_N1\) mechanisms. Because it is a \(1^{\circ}\) alkyl halide, we expect \(S_N2\) but not \(S_N1\) reactions. Draw a mechanism for the \(S_N1\) reaction shown below, paying careful attention to the structure of the intermediate. How can this primary halide undergo \(S_N1\) reactions?

The reaction of an amine with an alkyl halide gives an ammonium salt. The rate of this \(S_N2\) 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.

The following reaction takes place under second-order conditions (strong nucleophile), yet the structure of the product shows rearrangement. Also, the rate of this reaction is several thousand times faster than the rate of substitution of hydroxide ion on 2-chlorobutane under similar conditions. Propose a mechanism to explain the enhanced rate and rearrangement observed in this unusual reaction. (Et is the abbreviation for ethyl.) + Cl Et2N 2C CHH CH2CH3 OH OH NEt2 2C CHH CH2CH3 Cl

Propose mechanisms to account for the observed products in the following reactions. (a) Br Br NBS h + (a) (b) Br + CH2Br

Show the products you expect when each compound reacts with NBS with light shining on the reaction. (a)(a) (b) (b) (c)(c) O OCH3 (d) (d

A student adds NBS to a solution of 1-methylcyclohexene and irradiates the mixture with a sunlamp until all the NBS has reacted. After a careful distillation, the product mixture contains two major products of formula C7H11Br. (a) Draw the resonance forms of the three possible allylic free radical intermediates. (b) Rank these three intermediates from most stable to least stable. (c) Draw the products obtained from each free-radical intermediate.