1 750 CAPTER 6 TE CEITRY F BENZENE AND IT DERIVATIVE This hybridization allows one of its electron pairs to occupy a 2p orbital, which has the same size, shape, and orientation as the carbon 2p orbitals of the ring. In other words, an oxygen 2p orbital overlaps more effectively with the carbon 2p orbitals of the ring than an oxygen sp orbital would. (We learned about the same effect in resonance-stabilized allylic systems; p. 7). The UV spectrum of anisole is a direct consequence of this overlap. PRBLE 6.0 (a) Explain why compound A has a UV spectrum with considerably greater lmax values and intensities than are observed for ethyl. C 2 5 L L LC 2 5 l max = 256 nm (e = 20,000) 28 nm (e = 5,00) A (b) In view of your answer to part (a), explain why the UV spectra of compounds B and C are virtually identical. C C Lv $ C $ C $ B bimesityl l max = 266 nm (e = 700) C vl C i C $ % C C C mesitylene l max = 266 nm (e = 200) 6. ow could you distinguish styrene (PhLCAC 2 ) from ethyl by UV spectroscopy? 6.4 ELECTRPILIC ARATIC UBTITUTIN REACTIN F BENZENE The most characteristic reaction of and many of its derivatives is electrophilic aromatic substitution. In an electrophilic aromatic substitution reaction, a hydrogen of an aromatic ring is substituted by an electrophile that is, by a Lewis acid. The general pattern of an electrophilic aromatic substitution reaction is as follows, where E is the electrophile: L ELY L E L Y (6.) (Note that in this reaction and in others that follow, only one of the six hydrogens is shown explicitly to emphasize that one hydrogen is lost in the reaction.) All electrophilic aromatic substitution reactions occur by similar mechanisms. This section surveys some of the most common electrophilic aromatic substitution reactions and their mechanisms.
2 6.4 ELECTRPILIC ARATIC UBTITUTIN REACTIN F BENZENE 75 A. alogenation of Benzene When reacts with bromine under harsh conditions liquid bromine, no solvent, and the Lewis acid Fe as a catalyst a reaction occurs in which one bromine is substituted for a ring hydrogen. L 2 Fe or Fe (0.2 equiv.) L (6.2) bromo (50% yield) (Because iron reacts with 2 to give Fe, iron filings can be used in place of Fe.) An analogous chlorination reaction using Cl 2 and FeCl gives chloro. This reaction of with halogens differs from the reaction of alkenes with halogens in two important ways. First is the type of product obtained. Alkenes react spontaneously with bromine and chlorine, even in dilute solution, to give addition products. alogenation of, however, is a substitution reaction; a ring hydrogen is replaced by a halogen. econd, the reaction conditions for halogenation are much more severe than the conditions for addition of halogens to an alkene. The first step in the mechanism of bromination is the formation of a complex between 2 and the Lewis acid Fe. y 2 L Fe Formation of this complex results in a formal positive charge on one of the bromines. A positively charged bromine is a better electron acceptor, and thus a better leaving group, than a bromine in 2 itself. Another (and equivalent) explanation of the leaving-group effect is that Fe 4 is a weaker base than. (Remember from ec. 9.4F that weaker bases are better leaving groups.) Fe 4 is essentially the product of a Lewis acid base association reaction of with Fe. Therefore, in Fe 4, an electron pair on has already been donated to Fe, and is thus less available to act as a base, than a naked electron pair on itself. ` L LFe (6.) (6.4) a better electron acceptor and better leaving group a weaker electron acceptor and poorer leaving group Nuc (a nucleophile) L L Fe Nuc L Nuc L L Fe Nuc L (6.5) a weaker base a stronger base
3 752 CAPTER 6 TE CEITRY F BENZENE AND IT DERIVATIVE As you learned in ec. 9.4F, L is a good leaving group. The fact that a much better leaving group than L is required for electrophilic aromatic substitution illustrates how unreactive the ring is. In the second step of the mechanism, this complex reacts with the p electrons of the ring. The p electrons act as a nucleophile, the as an electrophile, and Fe 4 as a leaving group. electrophile nucleophile 2 L 2 L Fe / L leaving group 2 / 2 % 2 x % n % Fe 4 (6.6) Although this step results in the formation of a resonance-stabilized carbocation, it also disrupts the aromatic stabilization of the ring. arsh conditions (high reagent concentrations, high temperature, and a strong Lewis acid catalyst) are required for this reaction to proceed at a useful rate because this step does not occur under the much milder conditions used to bring about bromine addition to an alkene. The reaction is completed when a bromide ion (complexed to Fe ) acts as a base to remove the ring proton, regenerate the catalyst Fe, and give the products bromo and. 2 / % vl 2 2 Fe 2 L Fe (6.7) Recall that loss of a b-proton is one of the characteristic reactions of carbocations (ec. 9.6B). Another typical reaction of carbocations reaction of bromide ion at the electron-deficient carbon itself doesn t occur because the resulting addition product would not be aromatic: 2 L Fe ) 2 / % / % does not occur (not aromatic) Fe (6.8) By losing a b-proton instead (Eq. 6.7), the carbocation can form bromo, a stable aromatic compound. PRBLE 6.2 A small amount of a by-product, p-dibromo, is also formed in the bromination of shown in Eq Write a curved-arrow mechanism for formation of this compound.
4 6.4 ELECTRPILIC ARATIC UBTITUTIN REACTIN F BENZENE 75 B. Electrophilic Aromatic ubstitution alogenation of is one of many electrophilic aromatic substitution reactions. The bromination of, for example, is an aromatic substitution because a hydrogen of (the aromatic compound that undergoes substitution) is replaced by another group (bromine). The reaction is electrophilic because the substituting group reacts as an electrophile, or Lewis acid, with the p electrons. In bromination, the Lewis acid is a bromine in the complex of bromine and the Fe catalyst (Eq. 6.6). We ve considered two other types of substitution reactions: nucleophilic substitution (the N 2 and N reactions, ecs. 9.4 and 9.6) and free-radical substitution (halogenation of alkanes, ec. 8.9A). In a nucleophilic substitution reaction, the substituting group acts as a nucleophile, or Lewis base; and in free-radical substitution, free-radical intermediates are involved. Electrophilic aromatic substitution is the most typical reaction of and its derivatives. As you learn about other electrophilic substitution reactions, it will help you to understand them if you can identify in each reaction the following three mechanistic steps: tep tep 2 Generation of an electrophile. The electrophile in bromination is the complex of bromine with Fe, formed as shown in Eq Nucleophilic reaction of the p electrons of the aromatic ring with the electrophile to form a resonance-stabilized carbocation intermediate. a tetrahedral, sp -hybridized carbon; no longer involved in the p-electron system nucleophile electrophile E X leaving group E resonance-stabilized carbocation intermediate X.. (6.9a) The electrophile approaches the p-electron cloud of the ring above or below the plane of the molecule. In the carbocation intermediate, the carbon at which the electrophile reacts becomes sp -hybridized and tetrahedral. This step in the bromination mechanism is Eq tep Loss of a proton from the carbocation intermediate to form the substituted aromatic compound. The proton is lost from the carbon at which substitution occurs. This carbon again becomes part of the aromatic p-electron system. E X.. E X (6.9b) This step in the bromination mechanism is Eq This sequence is classified as electrophilic substitution because we focus on the nature of the group an electrophile that reacts with the aromatic ring. owever, the mechanism really involves nothing fundamentally new: like both electrophilic addition (ec. 5.) and nucleophilic substitution (ec. 9.), the reaction involves the reactions of nucleophiles, electrophiles, and leaving groups.
5 754 CAPTER 6 TE CEITRY F BENZENE AND IT DERIVATIVE tudy Problem 6. Give a curved-arrow mechanism for the following electrophilic substitution reaction. L D 2 4 L D olution Construct the mechanism in terms of the three preceding steps. tep tep 2 In this reaction, a hydrogen of the ring has been replaced by an isotope D, which must come from the D 2 4. Because protons (in the form of ønsted acids) are good electrophiles, the D 2 4 itself can serve as the electrophile. Reaction of the p electrons with the electrophile involves protonation of the ring by the isotopically substituted acid: i D L 2 D ) % a D 2 D resonance-stabilized carbocation intermediate (If you re asking where that extra hydrogen in the carbocation came from, don t forget that each carbon of the ring has a single hydrogen that is not shown explicitly in the skeletal structure. ne of these is shown in the carbocation because it is involved in the next step.) You should draw the resonance structures of the carbocation intermediate. tep Removal of the proton gives the final product: ) % a D 2 D D i L 2 D C. Nitration of Benzene Benzene reacts with concentrated nitric acid, usually in the presence of a sulfuric acid catalyst, to form nitro. In this reaction, called nitration, the nitro group, LN 2, is introduced into the ring by electrophilic substitution. 2 4 L N 2 L N 2 2 (6.0) nitric acid nitro (8% yield) This reaction fits the mechanistic pattern of the electrophilic aromatic substitution reaction outlined in the previous section: tep Generation of the electrophile. In nitration, the electrophile is N 2, the nitronium ion. This ion is formed by the acid-catalyzed removal of the elements of water from N.
6 6.4 ELECTRPILIC ARATIC UBTITUTIN REACTIN F BENZENE ) 2 L ) 5 L L (6.a) 2 ) 5 L L N A N nitronium ion (6.b) tep 2 Reaction of the p electrons with the electrophile to form a carbocation intermediate. 2 N N vl / # % (6.c) tep (Notice that either of the oxygens can accept the electron pair.) Loss of a proton from the carbocation to give a new aromatic compound. 2 N / # % 2 L 2 ) vl N L (from Eq. 6.a) Nitration is the usual way that nitro groups are introduced into aromatic rings. (6.d) D. ulfonation of Benzene Another electrophilic substitution reaction of is its conversion into sulfonic acid. L 2 4 L (6.2) sulfur trioxide sulfonic acid (52% yield) (ulfonic acids were introduced in ec. 0.A as their sulfonate ester derivatives.) This reaction, called sulfonation, occurs by two mechanisms that operate simultaneously. Both mechanisms involve sulfur trioxide, a fuming liquid that reacts violently with water to give 2 4. The source of for sulfonation is usually a solution of in concentrated 2 4 called fuming sulfuric acid or oleum. This material is one of the most acidic ønsted acids available commercially.
7 756 CAPTER 6 TE CEITRY F BENZENE AND IT DERIVATIVE In one sulfonation mechanism, the electrophile is neutral sulfur trioxide. When sulfur trioxide reacts with the ring p electrons, an oxygen accepts the electron pair displaced from sulfur. vl ( 2 ( A / ) $ vl L 2 L 2 2 (from solvent) vl L 2 2 (6.) ulfonic acids such as sulfonic acid are rather strong acids. (Notice the last equilibrium in Eq. 6. and the structural resemblance of sulfonic acid to another strong acid, sulfuric acid.) ulfonation, unlike many electrophilic aromatic substitution reactions, is reversible. The L (sulfonic acid) group is replaced by a hydrogen when sulfonic acids are heated with steam (Problem 6.50, p. 782). PRBLE 6. A second sulfonation mechanism involves protonated sulfur trioxide as the electrophile. how the protonation of, and draw a curved-arrow mechanism for the reaction of protonated with to give sulfonic acid. 6.4 A compound called p-toluenesulfonic acid is formed when toluene is sulfonated at the para position. Draw the structure of this compound, and give the curved-arrow mechanism for its formation. E. Friedel Crafts Alkylation of Benzene The reaction of an alkyl halide with in the presence of a Lewis acid catalyst gives an alkyl. L Cl LC LC 2 C AlCl (0. equiv.) L C L C 2 C Cl (6.4) (large excess) C sec-butyl chloride C sec-butyl (7% yield) This reaction is an example of a Friedel Crafts alkylation. Recall that an alkylation is a reaction that results in the transfer of an alkyl group (ec. 0.B). In a Friedel Crafts alkylation, an alkyl group is transferred to an aromatic ring in the presence of an acid catalyst. In the preceding example, the alkyl group comes from an alkyl halide and the catalyst is the Lewis acid aluminum trichloride, AlCl. The electrophile in a Friedel Crafts alkylation is formed by the complexation of the Lewis acid AlCl with the halogen of an alkyl halide in much the same way that the electrophile in
8 Cl 6.4 ELECTRPILIC ARATIC UBTITUTIN REACTIN F BENZENE 757 the bromination of is formed by the complexation of Fe with 2 (Eq. 6.4, p. 75). If the alkyl halide is secondary or tertiary, this complex can further react to form carbocation intermediates. R L AlCl R LCl L AlCl R AlCl 4 carbocation (6.5a) Either the alkyl halide Lewis acid complex, or the carbocation derived from it, can serve as the electrophile in a Friedel Crafts alkylation. R LCl L L AlCl alkylation by the complex or R AlCl 4 L R $ ) AlCl 4 (6.5b) alkylation by the carbocation Compare the role of AlCl in enhancing the effectiveness of the chloride leaving group with the similar role of Fe or FeCl in the bromination (Eq. 6.5, p. 75) or chlorination of : nucleophile electrophile electrophile nucleophile R L AlCl L Cl 2 2 L 2 L Fe (6.5c) /L /L complex formation with AlCl makes Cl a better leaving group complex formation with Fe makes a better leaving group We ve learned three general reactions of carbocations:. reaction with nucleophiles (ecs. 4.7B D, 9.6B) 2. rearrangement to other carbocations (ec. 4.7B). loss of a b-proton to give an alkene (ec. 9.6B) or aromatic ring (Eq. 6.7, ec. 6.4A) The reaction of a carbocation with the p electrons is an example of reaction. Loss of a proton to chloride ion completes the alkylation. R / vl R Cl % AlCl Cl L AlCl (6.5d) Because some carbocations can rearrange, it is not surprising that rearrangements of alkyl groups are observed in some Friedel Crafts alkylations:
9 758 CAPTER 6 TE CEITRY F BENZENE AND IT DERIVATIVE the alkyl group has rearranged L C C 2 C 2 C 2 Cl -chlorobutane AlCl 0 C Cl butyl (27% yield) C L C 2 C 2 C 2 C L CC 2 C sec-butyl (49% yield) (6.6) In this example, the alkyl group in the sec-butyl product has rearranged. Because primary carbocations are too unstable to be involved as intermediates, it is probably the complex of the alkyl halide and AlCl that rearranges. This complex has enough carbocation character that it behaves like a carbocation. C C 2 CC 2 LCl LAlCl C C 2 CC sec-butyl cation alkylates to give sec-butyl Cl L AlCl (6.7) As we might expect, rearrangement in the Friedel Crafts alkylation is not observed if the carbocation intermediate is not prone to rearrangement. AlCl (0.04 equiv.) L (C ) C L Cl L C(C ) (C ) C L LC(C ) Cl (threefold excess) tert-butyl (66% yield),4-di-tert-butyl (small amount) (6.8) In this example, the alkylating cation is the tert-butyl cation; because it is tertiary, this carbocation does not rearrange. Alkyls such as butyl (Eq. 6.6) that are derived from rearrangementprone alkyl halides are generally not prepared by the Friedel Crafts alkylation, but rather by other methods that we ll consider in ecs. 9.2 and 8.0B. Another complication in Friedel Crafts alkylation is that the alkyl products are more reactive than itself (for reasons discussed in ec. 6.5B). This means that the product can undergo further alkylation, and mixtures of products alkylated to different extents are observed. L C Cl AlCl toluene, xylenes, trimethyls, etc. (6.9) (equimolar amounts) (Notice also the product of double alkylation in Eq. 6.8.) owever, a monoalkylation product can be obtained in good yield if a large excess of the aromatic starting material is used. For example, in the following equation the 5-fold molar excess of ensures that a molecule of alkylating agent is much more likely to encounter a molecule of in the reaction mixture than a molecule of the ethyl product.
10 6.4 ELECTRPILIC ARATIC UBTITUTIN REACTIN F BENZENE 759 L Cl AlCl C2 C L C 2 C (6.20) (5-fold excess) ethyl chloride ethyl (8% yield) TUDY GUIDE LINK 6.2 Different ources of the ame Reactive Intermediate (Notice also the use of excess starting material in Eqs. 6.4 and 6.8.) This strategy is practical only if the starting material is cheap, and if it can be readily separated from the product. Alkenes and alcohols can also be used as the alkylating agents in Friedel Crafts alkylation reactions. The carbocation electrophiles in such reactions are generated from alkenes by protonation and from alcohols by dehydration. (Recall that carbocation intermediates are formed in the protonation of alkenes and dehydration of alcohols; ecs. 4.7B, 4.9B, 0..) C L (6.2) cyclohexene cyclohexyl (65 68% yield) PRBLE 6.5 (a) Give a curved-arrow mechanism for the reaction shown in Eq (b) Explain why the same product is formed if cyclohexanol is used instead of cyclohexene in this reaction. 6.6 What electrophilic substitution product is formed when 2-methylpropene is added to a large excess of containing F and the Lewis acid BF? By what mechanism is it formed? 6.7 Predict the product of the following reaction and give the curved-arrow mechanism for its formation. (int: Friedel Crafts alkylations can be used to form rings.) (a) AlCl C L L C 2 C 2 C 2 L Cl (a compound C 0 2 Cl) (b) AlCl L C 2 C 2 C 2 C 2L Cl (a compound C 0 2 Cl) F. Friedel Crafts Acylation of Benzene When reacts with an acid chloride in the presence of a Lewis acid such as aluminum trichloride (AlCl ), a ketone is formed. ) AlCl (. equiv.) 2) L Cl C C 2 L L L C L C Cl acetyl chloride (an acid chloride) acetophenone (a ketone) (97% yield) (6.22) This reaction is an example of a Friedel Crafts acylation (pronounced AY-suh-LAY-shun). In an acylation reaction, an acyl group is transferred from one group to another. In the
11 760 CAPTER 6 TE CEITRY F BENZENE AND IT DERIVATIVE Friedel Crafts acylation, an acyl group, typically derived from an acid chloride, is introduced into an aromatic ring in the presence of a Lewis acid. The electrophile in the Friedel Crafts acylation reaction is a carbocation called an acylium ion. This ion is formed when the acid chloride reacts with the Lewis acid AlCl. R L C L Cl an acid chloride R L C L Cl AlCl RL C A RL C' AlCl 4 Weaker Lewis acids, such as FeCl and ZnCl 2, can be used to form acylium ions in Friedel Crafts acylations of aromatic compounds that are more reactive than. The acylation reaction is completed by the usual steps of electrophilic aromatic substitution (ec. 6.4B): 2 C CL R vl / vl ) C L R Cl AlCl R Cl L AlCl Cl L AlCl acylium ion (6.2) (6.24) As we ll learn in ec. 9.6, ketones are weakly basic. Because of this basicity, the ketone product of the Friedel Crafts acylation reacts with the Lewis acid in a Lewis acid base association to form a complex that is catalytically inactive. This complex is the actual product of the acylation reaction. The formation of this complex has two consequences. First, at least one equivalent of the Lewis acid must be used to ensure its presence throughout the reaction. (Notice, for example, that. equivalent of AlCl is used in Eq ) This is in contrast to the Friedel Crafts alkylation, in which AlCl can be used in catalytic amounts. econd, the complex must be destroyed before the ketone product can be isolated. This is usually accomplished by pouring the reaction mixture into ice water. R L C L an acyl group AlCl L C L R L AlCl L C L R complex of AlCl with the ketone product 2 (6.25) L C L R Cl Al() Both Friedel Crafts alkylation and acylation reactions can occur intramolecularly when the product contains a five- or six-membered ring. (ee also Problem 6.7.)
12 6.4 ELECTRPILIC ARATIC UBTITUTIN REACTIN F BENZENE 76 r Cl L C C 2 C 2 C 2 ) AlCl 2) 2 r Cl (6.26) 4-phenylbutanoyl chloride a-tetralone (74 9% yield) In this reaction, the phenyl ring bites back on the acylium ion within the same molecule to form a bicyclic compound. This type of reaction can only occur at an adjacent ortho position because reaction at other positions would produce highly strained products. When five- or sixmembered rings are involved, this process is much faster than reaction of the acylium ion with the phenyl ring of another molecule. (ometimes this reaction can be used to form larger rings as well.) This is another illustration of the proximity effect: the kinetic advantage of intramolecular reactions (ec..7b). The multiply substituted products observed in Friedel Crafts alkylation (ec. 6.4E) are not a problem in Friedel Crafts acylation because the ketone products of acylation are much less reactive than the starting material, for reasons discussed in ec. 6.5B. The Friedel Crafts alkylation and acylation reactions are important for two reasons. First, the alkylation reaction is useful for preparing certain alkyls, and the acylation reaction is an excellent method for the synthesis of aromatic ketones. econd, they provide other ways to form carbon carbon bonds. ere is an updated list of reactions that form carbon carbon bonds.. addition of carbenes and carbenoids to alkenes (ec. 9.8) 2. reaction of Grignard reagents with ethylene oxide and lithium organocuprate reagents with epoxides (ec..4c). reaction of acetylenic anions with alkyl halides or sulfonates (ec. 4.7B) 4. Diels Alder reactions (ec. 5.) 5. Friedel Crafts reactions (ecs. 6.4E and 6.4F) Charles Friedel and James ason Crafts The Friedel Crafts acylation and alkylation (ec. 6.4E) reactions are named for their discoverers, the French chemist Charles Friedel (82 899) and the American chemist James ason Crafts (89 97). The two men met in Paris while in the laboratory of Charles Adolphe Wurtz (87 884), one of the most famous chemists of that time. In 877, Friedel and Crafts began their collaboration on the reactions that were to bear their names.friedel subsequently became a very active figure in the development of chemistry in France,and Crafts served for a time as president of the assachusetts Institute of Technology. PRBLE 6.8 Give the structure of the product expected from the reaction of each of the following compounds with in the presence of one equivalent of AlCl, followed by treatment with water. (a) (b) (C ) 2 C L C L Cl L C L Cl isobutyryl chloride benzoyl chloride
13 762 CAPTER 6 TE CEITRY F BENZENE AND IT DERIVATIVE 6.9 how two different Friedel Crafts acylation reactions that can be used to prepare the following compound. ) C cl C LcLC ) C 6.20 The following compound reacts with AlCl followed by water to give a ketone A with the formula C 0 0. Give the structure of A and a curved-arrow mechanism for its formation. C L L C 2 C 2 L C L Cl 6.5 ELECTRPILIC ARATIC UBTITUTIN REACTIN F UBTITUTED BENZENE A. Directing Effects of ubstituents i bromo When a monosubstituted undergoes an electrophilic aromatic substitution reaction, three possible disubstitution products might be obtained. For example, nitration of bromo could in principle give ortho-, meta-, or para-bromonitro. If substitution were totally random, an ortho:meta:para product ratio of 2 : 2 : would be expected. (Why?) It is found experimentally that this substitution is not random, but is regioselective. N acetic acid N 2 i o-bromonitro (6%) ther electrophilic substitution reactions of bromo also give mostly ortho and para isomers. If a substituted undergoes further substitution mostly at the ortho and para positions, the original substituent is called an ortho, para-directing group. Thus, bromine is an ortho, para-directing group, because all electrophilic substitution reactions of bromo occur at the ortho and para positions. In contrast, some substituted s react in electrophilic aromatic substitution to give mostly the meta disubstitution product. For example, the bromination of nitro gives only the meta isomer. N 2 N 2 i nitro i 2 Fe heat N 2 i (6.28) ther electrophilic substitution reactions of nitro also give mostly the meta isomers. If a substituted undergoes further substitution mainly at the meta position, the origi- p-bromonitro (62%) m-bromonitro (only product observed) i N 2 m-bromonitro (2%) (6.27)
19.1 Introduction to Electrophilic Aromatic Substitution In Chapter 18, we saw how aromatic C=C double bonds are less reactive than typical alkene double bonds. Consider a bromination reaction: 19.1 Introduction
Lecture otes Chem 51B S. King Chapter 18 Electrophilic Aromatic Substitution I. Electrophilic Aromatic Substitution The most characteristic reaction of aromatic compounds is electrophilic aromatic substitution,
KOT 222 ORGANIC CEMISTRY II CAPTER 17 REACTIONS of AROMATIC COMPOUNDS 1 Electrophilic Aromatic Substitution Substitution of an electrophile for a proton on the aromatic ring. benzene s pi electrons are
ORGANIC CHEMISTRY, 2 ND EDITION PAULA YURKANIS BRUICE Chapter 8 AROMATICITY REACTIONS OF BENZENE RAED M. AL-ZOUBI, ASSISTANT PROFESSOR OF CHEMISTRY DEPARTMENT OF CHEMISTRY - N 4 L 0 JORDAN UNIVERSITY OF
Chapter 17: Reactions of Aromatic Compounds Electrophilic aromatic substitution (17-1) Most common (normal) reaction of aromatics HNO 3 H 2 SO 4 NO 2 + H2O 452 Similar to alkenes, benzene (aromatics) has
508 CAPTR TWLV Reactions of s: lectrophilic Aromatic Substitution C3 CCC 3 BF 3 CC C 3 C 3 Furan Acetic anhydride 2-Acetylfuran (75 92%) Acetic acid The regioselectivity of substitution in furan is explained
1 Chemistry 232 Summer 2016 Quiz 2a KEY Name: (Please print, surname first) ID: Do all questions. Time available: 20 min. Total available marks: 20. Score for this quiz: Answers written partially or completely
Aromatic compounds GE 1 BENZENE Structure Primary analysis revealed benzene had an... empirical formula of and a molecular formula of 6 6 Q.1 Draw out some suitable structures which fit the molecular formula
Substitution Reactions of Benzene and Its Derivatives Benzene does not undergo electrophilic addition It undergoes electrophilic aromatic substitution maintaining the aromatic core Electrophilic aromatic
Electrophilic Aromatic Substitution Electrophilic substitution is the typical reaction type for aromatic rings. Generalized electrophilic aromatic substitution: E E Electrophile Lewis acid: may be or neutral.
Electrophilic Aromatic Substitution Reactions, Course Notes Archive, 1 Electrophilic Aromatic Substitution Reactions An organic reaction in which an electrophile substitutes a hydrogen atom in an aromatic
Friedel Crafts Acylation An acyl chloride or an acid anhydride is the source of the acyl group. A Lewis acid (AlCl 3 ) is required. The Mechanism for Friedel Crafts Acylation The electrophile adds to the
Reactions of Aromatic Compounds Aromatic compounds are stabilized by this aromatic stabilization energy Due to this stabilization, normal S N 2 reactions observed with alkanes do not occur with aromatic
Electrophilic Aromatic Substitution Electrophilic Aromatic Substitution: a reaction in which the hydrogen atom of an aromatic ring is replaced as a result of an electrophilic attack on the aromatic ring
1 (Continuation of Chapter 17 ) VIII. Friedel-Crafts Alkylation Carbocations are electrophiles, and can therefore be useful reagents for forming new C-C bonds in EAS processes. Friedal and Craft demonstrated
Electrophilic Reactions on Aromatic Compounds Monosubstitution Dr. Sapna Gupta Electrophilic Aromatic Substitution Arene (Ar-H) is the generic term for an aromatic hydrocarbon The aryl group (Ar) is derived
12. Alcohols and Phenols Based on McMurry s Organic Chemistry, 6 th edition Alcohols and Phenols Alcohols contain an OH group connected to a saturated C (sp 3 ) They are important solvents and synthesis
Electrophilic Addition vs. Substitution ( LEAVES!) Electrophilic Aromatic Substitution δ δ E E Y Y Reaction Coordinate Diagrams for the Two Benzene Reactions δ δ E E Y Y Electrophilic aromatic substitutions
Electrophilic Aromatic Substitution (EAS) is a substitution reaction usually involving the benzene ring; more specifically it is a reaction in which the hydrogen atom of an aromatic ring is replaced as
96 CAPTER 3 ACIDS AND BASES. TE CURVED-ARROW NOTATION and that the unshared electron pair (and negative charge) is shared equally by the two terminal carbons. C L C A C 1 allyl anion (c) Using the curved-arrow
s for Chapter 21 21 PRBLEM 1 All you have to do is to spot the aromatic rings in these compounds. t may not be as easy as you think and you should give some reasons for questionable decisions. C 2 colchicine:
0. ULFNATE AND INRGANIC ETER DERIVATIVE F ALCL 44 R 2 C L CR 2 carbocation Lewis acid base association X (halide ion) 2 $ R 2 C L CR 2 R R X C A C $ alkyl halide R R alkene $ $ Brønsted acid base reaction
Chapter 16: Chemistry of Benzene: lectrophilic Aromatic Substitution lectrophilic positively charged species searching for electron density Aromatic benzene ring with a high electron density Substitution
9.8 Substituent effects in the electrophilic substitution of an aromatic ring Substituents affect the reactivity of the aromatic ring Some substituents activate the ring, making it more reactive than benzene
arboxylic Acids arboxylic acids have one property that distinguishes them from most other organic compounds they re acidic. Now not as acidic as fuming sulfuric acid, but still pretty darned acidic. The
Chemistry 2030 Survey of Organic Chemistry Fall Semester 2013 Dr. Rainer Glaser Examination #2 Arenes, Electrophilic Aromatic Substitution, Stereochemistry, and Nucleophilic Substitution and Elimination.
Chapter 16 Conjugation, resonance, and dienes Conjugation relies on the partial overlap of p-orbitals on adjacent double or triple bonds. A common conjugated system involves 1,3-dienes, such as 1,3-butadiene.
CHEM 334L Organic Chemistry Laboratory Revision 3.1 A Friedel-Crafts Alkylation The Synthesis of 1,4-Di-tert-Butyl-2,5-Dimethoxybenzene In this laboratory exercise we will synthesize the compound 1,4-di-tert-butyl-2,5-dimethoxybenzene.
690 CAPTER 17 ARMATIC SUBSTITUTIN REACTINS PRBLEM 1713 Show the products of these reactions: S 3 a) 2 S 4 b) 2 S 4 c) 2 S 4 d) 2 S 4 177 Friedel-Crafts Alkylation Developed by C Friedel and J M Crafts,
17. REACTINS INVLVING ALLYLIC AND BENZYLIC RADICALS 793 As Eq. 17. shows, the products derived from the reaction of water at the ring carbons are not formed. The reason is that these products are not aromatic
Benzene and aromatic compounds (McMurry Ch. 15 & 16) C 6 H 6 is an unusually stable molecule that does NOT react like alkenes do A model was proposed by Kekule in 1865: The resonance hybrid model explains
rganic Lecture Series Reactions of Benzene & Its Derivatives Chapter 22 1 Reactions of Benzene rganic Lecture Series The most characteristic reaction of aromatic compounds is substitution at a ring carbon
Substitution reactions of carbonyl compounds at the α-position Carbonyl compounds are acidic at α-c (e.g. C 2 C ); this is because of the electrophilic nature of carbonyl C= bond. The pka values of simple
CHEM 211 CHAPTER 16 - Homework SHORT ANSWER Consider the Friedel-Crafts alkylation reaction below to answer the following question(s): 1. Refer to the reaction above. Draw the structure of the electrophilic
New Section 3 Page 1 2:37 PM Friedel-Crafts reaction: Mechanism: Carbocation is the reactive electrophile. AlCl4- picks up a proton. Limitations come from the mechanism: Carbocationic intermediates prone
Carboxylic Acids When a carbonyl carbon also bears a hydroxyl group, then these compounds are appreciably acidic, and are called carboxylic acids. R Carboxylic acids are classified according to the substituent
4.8 Electrophilic Aromatic Substitution Arene(Ar-H) is the generic term for an aromatic hydrocarbon The aryl group (Ar) is derived by removal of a hydrogen atom from an arene Aromatic compounds undergo
A STUDENT SHULD BE ABLE T: ARMATIC CMPUNDS 1. Name benzene derivatives given the structures, and draw the structures given the names. This includes: Monosubstituted benzenes named as derivatives of benzene:
Carboxylic Acid Derivatives and itriles Carboxylic Acid Derivatives: There are really only four things to worry about under this heading; acid chlorides, anhydrides, esters and amides. We ll start with
John E. McMurry www.cengage.com/chemistry/mcmurry Chapter 22 Carbonyl Alpha-Substitution Reactions The α Position The carbon next to the carbonyl group is designated as being in the α position Electrophilic
A STUDENT SHOULD BE ABLE TO: REACTIONS OF AROMATIC COMPOUNDS 1. Predict the product(s) of Electrophilic Aromatic Substitution (EAS), Nucleophilic Aromatic Substitution (S N Ar) and Elimination-Addition
ALKENES AND ALKYNES REACTINS A STUDENT W AS MASTERED TE MATERIAL IN TIS SECTIN SULD BE ABLE T: 1. Given the starting materials and reaction conditions, predict the products of the following reactions of
John E. McMurry http://www.cengage.com/chemistry/mcmurry Chapter 17 Alcohols and Phenols Alcohols and Phenols Alcohols contain an OH group connected to a saturated C (sp 3 ) They are important solvents
arbocations Based on a Fall 2001 hemistry 30B onors project by Patricia Young Tutorial ontents A. Introduction B. arbocation lassification. arbocation Stability D. arbocation Formation E. Three Fates of
24.6 Sources of Phenols Phenol is an important industrial chemical. Major use is in phenolic resins for adhesives and plastics. Annual U.S. production is about 4 billion pounds per year. Industrial Preparations
Aromaticity and eactions of Benzene ark College Benzene is a unique molecule it is highly unsaturated with 6 carbons and 6 hydrogens, it is planar, and has a high degree of symmetry. These features explain
Alkynes An alkyne is a hydrocarbon that contain a Carbon carbon triple bond. Acetylene, the simplest alkyne, widely used in industry for the synthesis of acetaldehyde, acetic acid, vinyl chloride O O H
Andrew Rosen Chapter 7 - Alkenes and Alkynes I 7.1 - Introduction - The simplest member of the alkenes has the common name of ethylene while the simplest member of the alkyne family has the common name
Chapter 8. Aromaticity Learning objectives: 1. Name benzene derivatives. 2. Recognize aromatic compounds. 3. Explain the trend for the acidity of substituted phenol using the concept of electrondonating
Electrophilic Addition Reactions Electrophilic addition reactions are an important class of reactions that allow the interconversion of C=C and C C into a range of important functional groups. Conceptually,
John E. McMurry www.cengage.com/chemistry/mcmurry Chapter 14 Conjugated Compounds and Ultraviolet Spectroscopy Conjugated and Nonconjugated Dienes Compounds can have more than one double or triple bond
hapter 13 Alkenes and Alkynes Types of Bonds Alkanes and haloalkanes consist of atoms held together by bonds. These can also be called sigma bonds (σ bonds) which means that the orbitals of each atom overlap
Reactions of Alcohols Alcohols are versatile organic compounds since they undergo a wide variety of transformations the majority of which are either oxidation or reduction type reactions. Normally: Oxidation
Chemistry 52 Final Exam Name: 10 March 2003 This exam has six questions, two cover pages, ten exam pages, and three scratch pages. Please check before beginning to make sure no questions or pages are missing.
Richard F. Daley and Sally J. Daley www.ochem4free.com rganic Chemistry Chapter 18 Aromatic Substitution Reactions 18.1 Mechanism of Aromatic Electrophilic Substitution 914 18.2 The itration of Benzene
Advanced Organic Chemistry THIRD EDITION Part A: Structure and Mechanisms FRANCIS A. CAREY and RICHARD J. SUNDBERG University of Virginia Charlottesville, Virginia PLENUM PRESS NEW YORK AND LONDON Contents
rganic Chemistry otes by Jim Maxka C 16: Reactions of Aromatic Compounds Topics: Aromatic compounds are less reactive than many other molecules because of their stability Formation of very T electrophiles
zonolysis of Alkenes 1 When 2-methyl-2-pentene reacts with ozone, the initial 1,2,3-trioxolane product is 144, but this rearranges to ozonide 145. If 145 is treated with hydrogen peroxide as above, one
Benzene 1 NT 87 90 ompound 87 has the formula 6 6, is known as benzene, and it is a hydrocarbon derived from petroleum distillates. Benzene is the parent compound for a class of compounds known as aromatic
EXPERIMENT 3 (Organic Chemistry II) Nitration of Aromatic Compounds: Preparation of methyl-m-nitrobenzoate Pahlavan/Cherif Purpose a) Study electrophilic aromatic substitution reaction (EAS) b) Study regioselectivity
Chapter 25 The Chemistry of Life: Organic Chemistry general characteristics of organic molecules introduction to hydrocarbons alkanes unsaturated hydrocarbons functional groups: alcohols and ethers compounds
Alkynes and Their Reactions Naming Alkynes Alkynes are named in the same general way that alkenes are named. In the IUPAC system, change the ane ending of the parent alkane name to the suffix yne. Choose
Introduction to Organic Chemistry Syllabus Day 1: Session 1 (evening session): 1. Introduction to Organic Chemistry: 2. General discussion about what is chemistry? 3. What is organic chemistry? 4. What
13.1 Alcohols and Phenols Alcohols possess a hydroxyl group ( OH). 13.1 Alcohols and Phenols Hydroxyl groups in natural compounds. Hydroxyl groups are extremely common in natural compounds. 13-1 13-2 13.1
1 Class XII Chemistry Chapter: Alcohols, Phenols And Ethers Top concepts: 1. Structure of alcohols, phenols and ethers: 2. Preparation of alcohols: 3. Preparation of phenols: 2 4. Physical properties of
Alkynes: An Introduction to Organic Synthesis Alkynes Hydrocarbons that contain carbon-carbon triple bonds Acetylene, the simplest alkyne is produced industrially from methane and steam at high temperature
Chapter 2 1) Balancing Equations Writing a Correct Mechanism 2) Using Arrows to show Electron Movement 3) Mechanisms in Acidic and Basic Media 4) Electron rich Species: Nucleophile or Base? 5) Trimolecular
ALLS: Properties & Preparation General formula: R-, where R is alkyl or substitued alkyl. Ar-: phenol - different properties. Nomenclature 1. ommon names: Name of alkyl group, followed by word alcohol.
INTDUCTIN T LEWIS ACID-BASE CEMISTY DEINITINS Lewis acids and bases are defined in terms of electron pair transfers. A Lewis base is an electron pair donor, and a Lewis acid is an electron pair acceptor.
340 14. Nucleophilic substitution at C= with loss of carbonyl oxygen Ph In Chapter 13 we saw this way of making a reaction go faster by raising the energy of the starting material. We also saw that the
Principles of Drug Action 1, pring 2005, Carboxylic Acids Part 2 Carboxylic Acid tructure and Chemistry: Part 2 Jack Deuiter IV. eactions of the Carboxylic Acid eactions Depending on their overall structure,
hemistry 222--Spring 2002--Third Problem Set Due 5/1/02 nswers Part. For the following reactions, give the predominant product. learly show stereochemistry when appropriate (that is, draw a structure that
Organic Chemistry II / CHEM 252 Chapter 16 Aldehydes and Ketones I. Nucleophilic Addition to the Carbonyl Group Bela Torok Department of Chemistry University of Massachusetts Boston Boston, MA 1 Nomenclature
Chapter 10 Conjugation in Alkadienes and Allylic Systems Chapter 10 suggested problems: I. The allyl group Class Notes A. B. The allyl group is both a common name and an accepted IUPAC name 1. Allyl alcohol
. 0 onjugated Systems hapter 0 onjugation in Alkadienes and Allylic Systems onjugated systems are those in which a π-bond is connected or conjugated (from the Latin conjugare which means to link r yoke
Study Guide Chapters 19-20 Alkanes, Alkenes and Alkynes 1) Carbon-Carbon Bonding in Alkanes (C-C), Alkenes (C=C) and Alkynes (C C). Understand the hybridization of atomic orbitals (ground state promotion
1 P a g e Chemistry Notes for class 12 Chapter 13 Amines Amines constitute an important class of organic compounds derived by replacing one or more hydrogen atoms ofnh 3 molecule by alkyl/aryl group(s).
EXPERIMENT 5 (Organic Chemistry II) Pahlavan/Cherif Dehydration of Alcohols - Dehydration of Cyclohexanol Purpose - The purpose of this lab is to produce cyclohexene through the acid catalyzed elimination
rganic Chemistry 32-235 Practice Exam #4 Part 1: 1. The correct IUPAC name for the following structure is. C 2 CC 2 C C 2 5-hexen-3-ol 3-hydroxy-5-hexene (E) 4-hydroxy-1-hexene 1-hexen-4-ol (D) Isohexen-3-ol,
Carbonyl Condensation Reactions (Conjugate Addition) If we look at resonance structures for conjugated carbonyl compounds (often called α,β-unsaturated compounds), we ll see that there are TW sites for
EM 341: rganic hemistry I at North Dakota tate University Final Exam - tudy Guide Reactions to know ubstitution of Alcohols R X R X N 1 ubstitution - N 2 ubstitution 3 carbocation best 2 carbocation ok
Alkynes: An Introduction to Organic Synthesis Based on McMurry s Organic Chemistry, 6 th edition, Chapter 8 Alkynes! Hydrocarbons that contain carbon-carbon triple bonds! Acetylene, the simplest alkyne