Organic Chemistry Second Edition David Klein Chapter 17

17. 1 Classes of Dienes • There are three categories for dienes • Cumulated

17. 1 Classes of Dienes • This chapter focuses on conjugated systems • Heteroatoms

17. 2 Conjugated Dienes • A sterically hindered base can be used to form

Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. Klein, Organic Chemistry

17. 2 Conjugated Dienes • Single bonds that are part of a conjugated pi

17. 2 Conjugated Dienes • The more s-character a carbon has, the shorter its

17. 2 Conjugated Dienes • HOW do heats of hydrogenation provide information about stability?

17. 2 Conjugated Dienes • HOW does conjugation affect stability? • Practice conceptual checkpoints

17. 2 Conjugated Dienes • Rank the following compounds in order of increasing stability

17. 2 Conjugated Dienes • In general, single bonds will freely rotate • The

17. 2 Conjugated Dienes • The s-cis and s-trans both allow for full pi

17. 2 Conjugated Dienes • Why is s-trans lower in energy? Copyright © 2015

17. 2 Conjugated Dienes • About 98% of the molecules are in the s-trans

17. 2 Conjugated Dienes • The highest energy conformer will not be conjugated Copyright

17. 4 Electrophilic Addition • Recall the Markovnikov addition of H-X to a C=C

17. 4 Electrophilic Addition • The pi electrons attack the acid to give the

17. 4 Electrophilic Addition • The resonance stabilized carbocation can be attacked by the

17. 4 Electrophilic Addition • The addition of bromine to a diene also gives

17. 5 Thermodynamic Control vs. Kinetic Control • The ratio of 1, 2 vs.

17. 5 Thermodynamic Control vs. Kinetic Control • Why are the products unequal in

17. 5 Thermodynamic Control vs. Kinetic Control • Predict the MAJOR product for the

17. 6 Intro to Pericyclic Reactions • Pericyclic reactions occur without ionic or free

17. 6 Intro to Pericyclic Reactions • There are three main types of pericyclic

17. 6 Intro to Pericyclic Reactions • Pericyclic reactions have 4 general features 1.

17. 6 Intro to Pericyclic Reactions • Changes in the number of pi and

17. 7 Diels-Alder Reactions • Diels-Alder reactions can be very useful • They allow

17. 7 Diels-Alder Reactions • The arrows could be drawn in a clockwise or

17. 7 Diels-Alder Reactions • Why do the products generally have lower free energy?

17. 7 Diels-Alder Reactions • Most Diels-Alder reactions are thermodynamically favored at low and

17. 7 Diels-Alder Reactions • The pi sigma conversion provides a (-)ΔH Copyright ©

17. 7 Diels-Alder Reactions • ΔS should be (-) – Two molecules combine to

17. 7 Diels-Alder Reactions • Given the signs for ΔH and –TΔS, how should

17. 7 Diels-Alder Reactions • In the Diels-Alder reaction, the reactants are generally classified

17. 7 Diels-Alder Reactions • When an electron withdrawing group is attached to the

17. 7 Diels-Alder Reactions • Diels-Alder reactions are stereospecific depending on whether the (E)

17. 7 Diels-Alder Reactions • A CΞC triple bond can also act as a

17. 7 Diels-Alder Reactions • Predict products for the following reactions Copyright © 2015

17. 7 Diels-Alder Reactions • Diels-Alder reactions can also be affected by diene structure

17. 7 Diels-Alder Reactions • Dienes that can only exist in an s-trans conformation

17. 7 Diels-Alder Reactions • Draw four potential bicyclic Diels-Alder products for the reaction

17. 7 Diels-Alder Reactions • When bicyclic systems form, the terms ENDO and EXO

17. 7 Diels-Alder Reactions • The electron withdrawing groups attached to dieneophiles tend to

17. 7 Diels-Alder Reactions • The Diels-Alder transition state that produces the ENDO product

17. 9 Electrocyclic reactions • Determine how the number of σ and π bonds

17. 9 Electrocyclic reactions • When substituents are present on the terminal carbons, stereoisomers

17. 9 Electrocyclic reactions • Often the energy present at room temperature is sufficient

17. 9 Electrocyclic reactions Molecular orbitals of pi systems (ethylene): Copyright © 2015 John

17. 9 Electrocyclic reactions Molecular orbitals of pi systems (butadiene): Copyright © 2015 John

17. 9 Electrocyclic reactions • The symmetry of the HOMO determines the outcome •

17. 9 Electrocyclic reactions • The terminal carbons rotate as they become sp 3

17. 9 Electrocyclic reactions • Use MO theory to explain the products for the

17. 9 Electrocyclic reactions • Predict the major product for the reaction below. Pay

17. 9 Electrocyclic reactions • Under photochemical conditions, light energy excites an electron from

17. 9 Electrocyclic reactions • Will the new excited HOMO react disrotatory or conrotatory?

17. 9 Electrocyclic reactions • Make the same MO analysis to predict the symmetryallowed

17. 9 Electrocyclic reactions • The disrotatory nature of the photochemical [2+2] electrocyclic ring-closing

17. 9 Electrocyclic reactions • The Woodward-Hoffmann rules for thermal and photochemical electrocyclic reactions

17. 10 Sigmatropic Rearrangements • Sigmatropic Rearrangements – a pericyclic reaction in which one

17. 10 Sigmatropic Rearrangements • The notation for sigmatropic rearrangements is different from reactions

17. 10 Sigmatropic Rearrangements • The reaction below is a [1, 5] sigmatropic rearrangement

17. 10 Sigmatropic Rearrangements • The Cope rearrangement is a [3, 3] sigmatropic reaction

17. 10 Sigmatropic Rearrangements • The Claisen rearrangement is a [3, 3] sigmatropic reaction

17. 10 Sigmatropic Rearrangements • Two pericyclic reactions occur in the biosynthesis of Vitamin

17. 12 Color • The visible region of the spectrum (400 -700 nm) is

17. 12 Color • The color observed by your eyes will be the opposite

17. 12 Color • Bleaching agents generally work by breaking up conjugation through an

Additional Practice Problems • Explain the relationship between heat of hydrogenation and stability of

Additional Practice Problems • Explain why the instability of electrons in a pi MO

Additional Practice Problems • Give a complete mechanism and predict the major product for

Additional Practice Problems • Predict the products and give necessary conditions for the compound

Additional Practice Problems • Predict the products for the electrocyclic ring-opening below with proper

Slides: 92

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17. 1 Classes of Dienes • There are three categories for dienes • Cumulated – pi bonds are adjacent • Conjugated – pi bonds are separated by exactly ONE single bond • Isolated – pi bonds are separated by any distance greater than ONE single bond Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. 17 -2 Klein, Organic Chemistry 2 e

17. 1 Classes of Dienes • There are three categories for dienes • Cumulated – pi bonds are perpendicular • Conjugated – pi bond overlap extends over the entire system • Isolated – pi bonds are separated by too great a distance to experience extra overlap Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. 17 -3 Klein, Organic Chemistry 2 e

17. 1 Classes of Dienes • This chapter focuses on conjugated systems • Heteroatoms may be involved in a conjugated system • Draw a picture of the molecule shown to the right indicating where the pi bonds are and how they overlap • Practice with conceptual checkpoint 17. 1 Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. 17 -4 Klein, Organic Chemistry 2 e

17. 2 Conjugated Dienes • A sterically hindered base can be used to form dienes while avoiding the competing substitution reaction • Practice with conceptual checkpoint 17. 2 Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. 17 -5 Klein, Organic Chemistry 2 e

17. 2 Conjugated Dienes • Single bonds that are part of a conjugated pi system are shorter than typical single bonds • What is a pm? • The hybridization of a carbon affects its bond length Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. 17 -7 Klein, Organic Chemistry 2 e

17. 2 Conjugated Dienes • The more s-character a carbon has, the shorter its bonds will be. WHY? • Practice with conceptual checkpoint 17. 3 Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. 17 -8 Klein, Organic Chemistry 2 e

17. 2 Conjugated Dienes • HOW do heats of hydrogenation provide information about stability? • WHY is energy released upon hydrogenation? Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. 17 -9 Klein, Organic Chemistry 2 e

17. 2 Conjugated Dienes • HOW does conjugation affect stability? • Practice conceptual checkpoints 17. 4 and 17. 5 Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. 17 -10 Klein, Organic Chemistry 2 e

17. 2 Conjugated Dienes • In general, single bonds will freely rotate • The two most stable rotational conformations for butadiene are the s-cis and s-trans • What does the “s” of s-cis and s-trans stand for? • Are there any other rotational conformations that you think might be possible? Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. 17 -12 Klein, Organic Chemistry 2 e

17. 2 Conjugated Dienes • The s-cis and s-trans both allow for full pi system overlap • Other possible conformations will be higher in energy • WHY? Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. 17 -13 Klein, Organic Chemistry 2 e

17. 4 Electrophilic Addition • Recall the Markovnikov addition of H-X to a C=C double bond from section 9. 3 • With a conjugated diene as the substrate, two products are observed Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. 17 -17 Klein, Organic Chemistry 2 e

17. 4 Electrophilic Addition • The pi electrons attack the acid to give the most stable carbocation • What intermediate would result if the H were added to any of the other carbons in the molecule? Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. 17 -18 Klein, Organic Chemistry 2 e

17. 4 Electrophilic Addition • The resonance stabilized carbocation can be attacked by the halide at either site that is sharing the (+) charge • How is 1, 2 -addition different from 1, 4 -addition? • Practice with Skill. Builder 17. 1 Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. 17 -19 Klein, Organic Chemistry 2 e

17. 4 Electrophilic Addition • The addition of bromine to a diene also gives both 1, 2 and 1, 4 addition • Predict the MAJOR products for the reaction below. Pay close attention to stereochemistry Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. 17 -23 Klein, Organic Chemistry 2 e

17. 5 Thermodynamic Control vs. Kinetic Control • The ratio of 1, 2 vs. 1, 4 addition is often temperature dependant • The energy diagram must be examined to see WHY temperature affects the product distribution Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. 17 -24 Klein, Organic Chemistry 2 e

17. 5 Thermodynamic Control vs. Kinetic Control • Predict the MAJOR product for the following reactions ° Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. ° 17 -26 Klein, Organic Chemistry 2 e

17. 6 Intro to Pericyclic Reactions • Pericyclic reactions occur without ionic or free radical intermediates • There are three main types of pericyclic reactions 1. Cycloaddition reactions • How is it an addition reaction? Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. 17 -29 Klein, Organic Chemistry 2 e

17. 6 Intro to Pericyclic Reactions • There are three main types of pericyclic reactions 2. Electrocyclic reactions 3. Sigmatropic rearrangements • What is the difference between an addition and a rearrangement? Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. 17 -30 Klein, Organic Chemistry 2 e

17. 6 Intro to Pericyclic Reactions • Pericyclic reactions have 4 general features 1. The reaction mechanism is concerted. It proceeds without any intermediates 2. The mechanism involves a ring of electrons moving around a closed loop 3. The transition state is cyclic 4. The polarity of the solvent generally has no effect on the reaction rate. WHY is that significant? Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. 17 -31 Klein, Organic Chemistry 2 e

17. 6 Intro to Pericyclic Reactions • Changes in the number of pi and sigma bonds distinguish the pericyclic reactions from one another Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. 17 -32 Klein, Organic Chemistry 2 e

17. 7 Diels-Alder Reactions • Diels-Alder reactions can be very useful • They allow a synthetic chemist to quickly build molecular complexity • What is meant by [4+2] cycloaddition? • Like all pericyclic reactions, the mechanism is concerted Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. 17 -33 Klein, Organic Chemistry 2 e

17. 7 Diels-Alder Reactions • The arrows could be drawn in a clockwise or counterclockwise direction • Can you draw a reasonable transition state? Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. 17 -34 Klein, Organic Chemistry 2 e

17. 7 Diels-Alder Reactions • Most Diels-Alder reactions are thermodynamically favored at low and moderate temperatures • At temperatures above 200 C, the retro. Diels-Alder can predominate • Will the reaction probably be favored or disfavored by entropy? Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. 17 -36 Klein, Organic Chemistry 2 e

17. 7 Diels-Alder Reactions • ΔS should be (-) – Two molecules combine to form ONE – A ring (with limited rotational freedom) forms • What will the sign (+/-) be for the –TΔS term? Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. 17 -38 Klein, Organic Chemistry 2 e

17. 7 Diels-Alder Reactions • Given the signs for ΔH and –TΔS, how should temperature affect reaction spontaneity (reactant vs. product favorability)? • Are there any disadvantages if the temperature is too low? Think kinetics Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. 17 -39 Klein, Organic Chemistry 2 e

17. 7 Diels-Alder Reactions • In the Diels-Alder reaction, the reactants are generally classified as either the diene or dienophile • If a dienophile is not substituted with an electron withdrawing group, it will not be kinetically favored (a lot of activation energy or high temperature is required) • However, high temps do not favor the products thermodynamically Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. 17 -40 Klein, Organic Chemistry 2 e

17. 7 Diels-Alder Reactions • When an electron withdrawing group is attached to the dienophile, the reaction is generally spontaneous • Show the groups highlighted in red are electron withdrawing using resonance and induction where appropriate Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. 17 -41 Klein, Organic Chemistry 2 e

17. 7 Diels-Alder Reactions • Diels-Alder reactions are stereospecific depending on whether the (E) or (Z) dienophile is used • Which alkene is (E) and which is (Z)? • We will investigate the stereochemical outcome later in this chapter Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. 17 -42 Klein, Organic Chemistry 2 e

17. 7 Diels-Alder Reactions • A CΞC triple bond can also act as a dienophile • Practice with Skill. Builder 17. 3 Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. 17 -43 Klein, Organic Chemistry 2 e

17. 7 Diels-Alder Reactions • Diels-Alder reactions can also be affected by diene structure • Recall that many dienes can exist in an s-cis or an s-trans rotational conformation • Which conformation is generally more stable, and WHY? • Diels-Alder reactions can ONLY proceed when the diene adopts the s-cis conformation Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. 17 -47 Klein, Organic Chemistry 2 e

17. 7 Diels-Alder Reactions • Dienes that can only exist in an s-trans conformation can not undergo Diels-Alder reactions, because carbons 1 and 4 are too far apart 4 1 • Dienes that are locked into the s-cis conformation undergo Diels-Alder reactions readily • Cyclopentadiene is so reactive, that at room temperature, two molecule will react together. Show the reaction and products Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. 17 -48 Klein, Organic Chemistry 2 e

17. 7 Diels-Alder Reactions • Draw four potential bicyclic Diels-Alder products for the reaction below • Two of the potential stereoisomers are impossible. WHICH ones and WHY? Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. 17 -49 Klein, Organic Chemistry 2 e

17. 7 Diels-Alder Reactions • When bicyclic systems form, the terms ENDO and EXO are used to describe functional group positioning Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. 17 -50 Klein, Organic Chemistry 2 e

17. 7 Diels-Alder Reactions • The electron withdrawing groups attached to dieneophiles tend to occupy the ENDO position Major Product Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. 17 -51 Minor Product Klein, Organic Chemistry 2 e

17. 7 Diels-Alder Reactions • The Diels-Alder transition state that produces the ENDO product benefits from favorable pi system interactions • Is this a kinetic or thermodynamic argument? • Draw an appropriate energy diagram • Practice with conceptual checkpoint 17. 19 Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. 17 -52 Klein, Organic Chemistry 2 e

17. 9 Electrocyclic reactions • Determine how the number of σ and π bonds change for the representative electrocyclic reactions below • Explain why the equilibrium favor either products or reactants in the examples above Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. 17 -55 Klein, Organic Chemistry 2 e

17. 9 Electrocyclic reactions • When substituents are present on the terminal carbons, stereoisomers are possible • Note that the use of light versus heat gives different products. See next few slides for explanation Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. 17 -56 Klein, Organic Chemistry 2 e

17. 9 Electrocyclic reactions • Often the energy present at room temperature is sufficient to promote thermal electrocyclic reactions • Note that with the use heat, the configuration of the reactant determines the product formed Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. 17 -57 Klein, Organic Chemistry 2 e

17. 9 Electrocyclic reactions • The symmetry of the HOMO determines the outcome • The terminal carbons rotate as they become sp 3 hybridized and overlap lobes that are in phase Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. 17 -60 Klein, Organic Chemistry 2 e

17. 9 Electrocyclic reactions • The terminal carbons rotate as they become sp 3 hybridized and overlap lobes that are in phase • Disrotatory rotation (one rotates clockwise and the other counterclockwise) gives the cis product Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. 17 -61 Klein, Organic Chemistry 2 e

17. 9 Electrocyclic reactions • Use MO theory to explain the products for the reactions below • Will disrotatory or conrotatory rotation be necessary? • Practice with conceptual checkpoint 17. 21 Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. 17 -62 Klein, Organic Chemistry 2 e

17. 9 Electrocyclic reactions • Predict the major product for the reaction below. Pay close attention to stereochemistry Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. 17 -64 Klein, Organic Chemistry 2 e

17. 9 Electrocyclic reactions • Under photochemical conditions, light energy excites an electron from the HOMO to the LUMO • What was the LUMO becomes the new HOMO Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. 17 -65 Klein, Organic Chemistry 2 e

17. 9 Electrocyclic reactions • Will the new excited HOMO react disrotatory or conrotatory? • Draw the expected product Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. 17 -66 Klein, Organic Chemistry 2 e

17. 9 Electrocyclic reactions • Make the same MO analysis to predict the symmetryallowed product for the reaction below. Pay close attention to stereochemistry Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. 17 -67 Klein, Organic Chemistry 2 e

17. 9 Electrocyclic reactions • The disrotatory nature of the photochemical [2+2] electrocyclic ring-closing is difficult to observe directly, because thermodynamically favors ring opening • The ring-opening reaction gives products that result from disrotatory rotation. Predict products below Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. 17 -68 Klein, Organic Chemistry 2 e

17. 9 Electrocyclic reactions • The Woodward-Hoffmann rules for thermal and photochemical electrocyclic reactions are found in table 17. 2 • Practice with Skill. Builder 17. 4 Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. 17 -69 Klein, Organic Chemistry 2 e

17. 10 Sigmatropic Rearrangements • Sigmatropic Rearrangements – a pericyclic reaction in which one sigma bond is replaced with another • Note that the pi bonds move their location Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. 17 -74 Klein, Organic Chemistry 2 e

17. 10 Sigmatropic Rearrangements • The notation for sigmatropic rearrangements is different from reactions we have seen so far • Count the number of atoms on each side of the sigma bonds that are breaking and forming • This is a [3, 3] sigmatropic rearrangement Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. 17 -75 Klein, Organic Chemistry 2 e

17. 10 Sigmatropic Rearrangements • The reaction below is a [1, 5] sigmatropic rearrangement • Practice with conceptual checkpoint 17. 25 Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. 17 -76 Klein, Organic Chemistry 2 e

17. 10 Sigmatropic Rearrangements • The Cope rearrangement is a [3, 3] sigmatropic reaction in which all 6 atoms in the cyclic transition state are CARBONS • In general, what factors affect the spontaneity of the reaction (product favored vs. reactant favored)? • Practice with conceptual checkpoint 17. 26 Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. 17 -79 Klein, Organic Chemistry 2 e

17. 10 Sigmatropic Rearrangements • The Claisen rearrangement is a [3, 3] sigmatropic reaction in which one of the 6 atoms in the cyclic transition state is an OXYGEN • In general, what factors affect the spontaneity of the reaction? • Practice with conceptual checkpoints 17. 27 and 17. 28 Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. 17 -81 Klein, Organic Chemistry 2 e

17. 12 Color • The visible region of the spectrum (400 -700 nm) is lower energy than UV radiation • Lycopene is responsible for the red color of tomatoes • Β-carotene is responsible for the orange color of carrots Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. 17 -84 Klein, Organic Chemistry 2 e

17. 12 Color • The color observed by your eyes will be the opposite of what is required to cause the π π* excitation. WHY? • Practice with conceptual checkpoint 17. 31 Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. 17 -85 Klein, Organic Chemistry 2 e

17. 12 Color • Bleaching agents generally work by breaking up conjugation through an addition reaction • Destroying long range conjugation destroys the ability to absorb colored light. WHY? • Does bleach actually remove stains? Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. 17 -87 Klein, Organic Chemistry 2 e

Additional Practice Problems • Explain the relationship between heat of hydrogenation and stability of a pi system. Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. 17 -88 Klein, Organic Chemistry 2 e

Additional Practice Problems • Explain why the instability of electrons in a pi MO directly relates to the number of nodes the orbital posses. Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. 17 -89 Klein, Organic Chemistry 2 e

Additional Practice Problems • Give a complete mechanism and predict the major product for the addition reaction below. Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. 17 -90 Klein, Organic Chemistry 2 e

Additional Practice Problems • Predict the products and give necessary conditions for the compound below to undergo a retro Diels-Alder Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. 17 -91 Klein, Organic Chemistry 2 e

Additional Practice Problems • Predict the products for the electrocyclic ring-opening below with proper stereochemical configuration. Copyright © 2015 John Wiley & Sons, Inc. All rights reserved. 17 -92 Klein, Organic Chemistry 2 e