CHAPTER 11 ARENES AND AR○ MATICITY SOLUTIONS TO TEXT PROBLEMS 11.1 Toluene is C Hs CH3; it has a methyl group attached to a benzene ring Kekule forms of toluene Robinson symbol for toluene Benzoic acid has a-CO, H substituent on the benzene ring. COH Kekule forms of benzoic acid Robinson symbol for benzoic acid △H°=-110kJ(-26.3kcal d assuming that there is no resonance stabilization in 1,3,5-cycloheptatriene, we predict that its heat of hydrogenation will be three times that of cycloheptene or 330 kJ/mol (78.9 kcal/mol) 253 Back Forward Main Menu TOC Study Guide Toc Student OLC MHHE Website
253 CHAPTER 11 ARENES AND AROMATICITY SOLUTIONS TO TEXT PROBLEMS 11.1 Toluene is C6H5CH3; it has a methyl group attached to a benzene ring. Benzoic acid has a @CO2H substituent on the benzene ring. 11.2 Given and assuming that there is no resonance stabilization in 1,3,5-cycloheptatriene, we predict that its heat of hydrogenation will be three times that of cycloheptene or 330 kJ/mol (78.9 kcal/mol). Cycloheptene Cycloheptane H2 H 110 kJ (26.3 kcal) CO2H Robinson symbol for benzoic acid Kekulé forms of benzoic acid CO2H CO2H Kekulé forms of toluene CH3 CH3 Robinson symbol for toluene CH3 Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website
254 ARENES AND AROMATICITY The measured heat of hydrogenation is SH, r-uo() 1, 3. 5-Cycloheptatriene Cycloheptane Therefore Resonance energy =330 k/mol(predicted for no delocalization)-305 kJ/mol (observed 25 kJ/mol(5.9 kcal/mol) The value given in the text for the resonance energy of benzene(152 kj/mol) is six times larger than this. 1,3,5-Cycloheptatriene is not aromatic 11.3(b) The parent compound is styrene, CSHS CH=CH,. The desired compound has a chlorine in the prostyrene (c) The parent compound is aniline, C6HSNH2. p-Nitroaniline is therefore NH NO, 11.4 The most stable resonance form is the one that has the greatest number of rings that correspond to Kekule formulations of benzene For chrysene, electrons are moved in pairs from the structure given to generate a more stable one 〔人 ess stable: two rings have More stable: four rings have benzene bonding pattern. benzene bonding pat 11.5 Birch reductions of monosubstituted arenes yield 1, 4-cyclohexadiene derivatives in which the alkyl group is a substituent on the double bond With p-xylene, both methyl groups are double-bond sub stituents in the product CH CH, CH2OH H 3C H3 Xylene 1, 4-Dimethyl-1,4- Back Forward Main Menu TOC Study Guide Toc Student OLC MHHE Website
254 ARENES AND AROMATICITY The measured heat of hydrogenation is Therefore Resonance energy 330 kJ/mol (predicted for no delocalization) 305 kJ/mol (observed) 25 kJ/mol (5.9 kcal/mol) The value given in the text for the resonance energy of benzene (152 kJ/mol) is six times larger than this. 1,3,5-Cycloheptatriene is not aromatic. 11.3 (b) The parent compound is styrene, C6H5CH?CH2. The desired compound has a chlorine in the meta position. (c) The parent compound is aniline, C6H5NH2. p-Nitroaniline is therefore 11.4 The most stable resonance form is the one that has the greatest number of rings that correspond to Kekulé formulations of benzene. For chrysene, electrons are moved in pairs from the structure given to generate a more stable one: 11.5 Birch reductions of monosubstituted arenes yield 1,4-cyclohexadiene derivatives in which the alkyl group is a substituent on the double bond. With p-xylene, both methyl groups are double-bond substituents in the product. H3C CH3 p-Xylene H3C CH3 1,4-Dimethyl-1,4- cyclohexadiene Na, NH3 CH3CH2OH More stable: four rings have benzene bonding pattern. Less stable: two rings have benzene bonding pattern. NH2 NO2 p-Nitroaniline m-Chlorostyrene CH Cl CH2 3H2 H 305 kJ (73.0 kcal) 1,3,5-Cycloheptatriene Cycloheptane Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website
ARENES AND ARO 255 11.6(b) Only the benzylic hydrogen is replaced by bromine in the reaction of 4-methyl-3-nitroanisole with N-bromosuccinimide OCH OCH Only these hydrogens 11.7 The lecular formula of the product is CuH,O4. Since it contains four oxygens, the product must have two-CO,H groups. None of the hydrogens of a tert-butyl substituent on a benzene i benzylic, and so this group is inert to oxidation. Only the benzylic methyl groups of 4-tert-butyl-1, 2 dimethylbenzene are susceptible to oxidation; therefore, the product is 4-tert-butylbenzene-1, 2 dicarboxylic acid. (CH3)C. (CH3)3C Nac y to oxidation 1, 2-dicarboxylic acid 11.8 Each of these reactions involves nucleophilic substitution of the SN2 type at the benzylic position of (b)(CH3)3C CH,OC(CH3) tert-Butoxid Benzyl bromide Benzyl ter-butyl ether (c) =N=N: CH-Br CHN Azide i (d) HS CH—B CHSH CH,I lodide ion Benzyl bromide Back Forward Main Menu TOC Study Guide Toc Student OLC MHHE Website
11.6 (b) Only the benzylic hydrogen is replaced by bromine in the reaction of 4-methyl-3-nitroanisole with N-bromosuccinimide. 11.7 The molecular formula of the product is C12H14O4. Since it contains four oxygens, the product must have two @CO2H groups. None of the hydrogens of a tert-butyl substituent on a benzene ring is benzylic, and so this group is inert to oxidation. Only the benzylic methyl groups of 4-tert-butyl-1,2- dimethylbenzene are susceptible to oxidation; therefore, the product is 4-tert-butylbenzene-1,2- dicarboxylic acid. 11.8 Each of these reactions involves nucleophilic substitution of the SN2 type at the benzylic position of benzyl bromide. (b) (c) (d) (e) CH2I Benzyl iodide CH2 Br Benzyl bromide I Iodide ion CH2SH Phenylmethanethiol CH2 Br Benzyl bromide HS Hydrogen sulfide ion N N CH2N Benzyl azide CH2 Br Benzyl bromide N N N Azide ion CH2OC(CH3)3 Benzyl tert-butyl ether CH2 Br Benzyl bromide (CH3)3CO tert-Butoxide ion CH3 CH3 (CH3)3C Susceptible to oxidation Not benzylic hydrogens; not readily oxidized Na2Cr2O7 H2O, H2SO4, heat CO2H CO2H (CH3)3C 4-tert-Butylbenzene- 1,2-dicarboxylic acid CH2Br OCH3 NO2 CH3 OCH3 NO2 Only these hydrogens are benzylic. NBS 80C, peroxides ARENES AND AROMATICITY 255 Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website
256 ARENES AND AROMATICITY 11.9 The dihydronaphthalene in which the double bond is conjugated with the aromatic ring is more sta ble; thus 1, 2-dihydronaphthalene has a lower heat of hydrogenation than 1, 4-dihydronaphthalene 1, 2-Dihydronaphthalene 1. 4-Dihydronapht Heat 11.10 (b) The regioselectivity of alcohol formation by hydroboration-oxidation is opposite that pre- dicted by Markovnikov's rule C=CH2.HO HOT CHCH,OH (c) Bromine adds to alkenes in aqueous solution to give bromohydrin. a water molecule acts as a nucleophile, attacking the bromonium ion at the carbon that can bear most of the positiv charge, which in this case is the benzylic carbon CH=CH 2-Bromo-l-phenylethanol(82%) (d) Peroxy acids convert alkenes to epoxides. CH=CH COOH CH—CH,+ COH Peroxybenzoic acid Benzoic acid (69-75%) 11.11 Styrene contains a benzene ring and will be appreciably stabilized by resonance, which makes it lower in energy than cyclooctatetraene CHECH ontains an atic ning. 11.12 The dimerization of cyclobutadiene is a Diels-Alder reaction in which one molecule of cyclobuta diene acts as a diene and the other as a dienophile Diels-Alder adduct 11.13 (b) Since twelve 2p orbitals contribute to the cyclic conjugated system of [12]-annulene, there will be 12 T molecular orbitals. These MOs are arranged so that one is of highest energy, one is of lowest energy, and the remaining ten are found in pairs between the highest and lowest Back Forward Main Menu TOC Study Guide Toc Student OLC MHHE Website
11.9 The dihydronaphthalene in which the double bond is conjugated with the aromatic ring is more stable; thus 1,2-dihydronaphthalene has a lower heat of hydrogenation than 1,4-dihydronaphthalene. 11.10 (b) The regioselectivity of alcohol formation by hydroboration–oxidation is opposite that predicted by Markovnikov’s rule. (c) Bromine adds to alkenes in aqueous solution to give bromohydrins. A water molecule acts as a nucleophile, attacking the bromonium ion at the carbon that can bear most of the positive charge, which in this case is the benzylic carbon. (d) Peroxy acids convert alkenes to epoxides. 11.11 Styrene contains a benzene ring and will be appreciably stabilized by resonance, which makes it lower in energy than cyclooctatetraene. 11.12 The dimerization of cyclobutadiene is a Diels–Alder reaction in which one molecule of cyclobutadiene acts as a diene and the other as a dienophile. 11.13 (b) Since twelve 2p orbitals contribute to the cyclic conjugated system of [12]-annulene, there will be 12 molecular orbitals. These MOs are arranged so that one is of highest energy, one is of lowest energy, and the remaining ten are found in pairs between the highest and lowest Diene Dienophile Diels–Alder adduct CH CH2 Structure contains an aromatic ring. Styrene: heat of combustion 4393 kJ/mol (1050 kcal/mol) Cyclooctatetraene (not aromatic): heat of combustion 4543 kJ/mol (1086 kcal/mol) Styrene CH CH2 Epoxystyrene (69–75%) CH CH2 O Peroxybenzoic acid COOH O Benzoic acid COH O CH Styrene 2-Bromo-1-phenylethanol (82%) Br2 H2O CHCH2Br OH CH2 2-Phenylpropene C CH2 CH3 CH3 2-Phenyl-1-propanol (92%) 1. B2H6 2. H2O2, HO CHCH2OH 1,2-Dihydronaphthalene Heat of hydrogenation 101 kJ/mol (24.1 kcal/mol) 1,4-Dihydronaphthalene Heat of hydrogenation 113 kJ/mol (27.1 kcal/mol) 256 ARENES AND AROMATICITY Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website
ARENES AND ARO 257 energy orbitals. There are 12 T electrons, and so the lowest 5 orbitals are each doubly occu- ied, whereas each of the next 2 orbitals--orbitals of equal energy-is singly occupied Antibonding orbitals (5) Bonding orbitals (5) 11 14 One way to evaluate the relationship between heats of combustion and structure for compounds that are not isomers is to divide the heat of combustion by the number of carbons so that heats of com- bustion are compared on a " per carbon"basis Cyclooctatetraene [161-Annulene [181-Annulene 3265Jm 4543 k/mol 9121 k/mol 9806 k/mol (2182 kcal/mol) (2346 kcal/mol) 544 k/mol 568 kJ/mol 570 k/mol (130 kcal/mol) (136 kcal/mol) (130 kcal/mol) As the data indicate(within experimental error), the heats of combustion per carbon of the two aro- matic hydrocarbons, benzene and [18]-annulene, are equal. Similarly, the heats of combustion per carbon of the two nonaromatic hydrocarbons, cyclooctatetraene and [16]-annulene, are equal. The two aromatic hydrocarbons have heats of combustion per carbon that are less than those of the nonaromatic hydrocarbons. On a per carbon basis, the aromatic hydrocarbons have lower potential energy(are more stable) than the nonaromatic hydrocarbons 11.15 The seven resonance forms for tropylium cation(cycloheptatrienyl cation) may be generated by moving T electrons in pairs toward the positive charge. The resonance forms are simply a succes- sion of allylic carbocations H H Back Forward Main Menu TOC Study Guide Toc Student OLC MHHE Website
energy orbitals. There are 12 electrons, and so the lowest 5 orbitals are each doubly occupied, whereas each of the next 2 orbitals—orbitals of equal energy—is singly occupied. 11.14 One way to evaluate the relationship between heats of combustion and structure for compounds that are not isomers is to divide the heat of combustion by the number of carbons so that heats of combustion are compared on a “per carbon” basis. As the data indicate (within experimental error), the heats of combustion per carbon of the two aromatic hydrocarbons, benzene and [18]-annulene, are equal. Similarly, the heats of combustion per carbon of the two nonaromatic hydrocarbons, cyclooctatetraene and [16]-annulene, are equal. The two aromatic hydrocarbons have heats of combustion per carbon that are less than those of the nonaromatic hydrocarbons. On a per carbon basis, the aromatic hydrocarbons have lower potential energy (are more stable) than the nonaromatic hydrocarbons. 11.15 The seven resonance forms for tropylium cation (cycloheptatrienyl cation) may be generated by moving electrons in pairs toward the positive charge. The resonance forms are simply a succession of allylic carbocations. H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H Benzene Heats of combustion: 3265 kJ/mol (781 kcal/mol) Heats of combustion per carbon: 544 kJ/mol (130 kcal/mol) Cyclooctatetraene 4543 kJ/mol (1086 kcal/mol) 568 kJ/mol (136 kcal/mol) [16]-Annulene 9121 kJ/mol (2182 kcal/mol) 570 kJ/mol (136 kcal/mol) [18]-Annulene 9806 kJ/mol (2346 kcal/mol) 545 kJ/mol (130 kcal/mol) Antibonding orbitals (5) Nonbonding orbitals (2) Bonding orbitals (5) ARENES AND AROMATICITY 257 Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website
258 ARENES AND AROMATICITY 11.16 Resonance structures are generated for cyclopentadienide anion by moving the unshared electron pair from the carbon to which it is attached to a position where it becomes a shared electron pair in a丌bond H H 11. 17 The process is an acid-base reaction in which cyclopentadiene transfers a proton to amide ion( the base)to give the aromatic cyclopentadienide anion. The sodium ion(Nat) has been omitted from the equation. H H, H NH3 ,3-Cyclopentadiene Amide ion Cyclopentadienide Ammonia 11.18 (b) Cyclononatetraenide anion has 10 T electrons; it is aromatic. The 10 T electrons are most easily seen by writing a Lewis structure for the anion: there are 2 T electrons for each of four double bonds, and the negatively charged carbon contributes 2 11.19 Indole is more stable than isoindole. Although the bonding patterns in both five-membered rings are the same, the six-membered ring in indole has a pattern of bonds identical to benzene and so is highly stabilized. The six-membered ring in isoindole is not of the benzene type Six-membered Six-membered ring does nh not have same pattern of to benzene bonds as benzene Indole Isoindole more stable less stable 11.20 The prefix benz- in benzimidazole(structure given in text) signifies that a benzene ring is fused to n imidazole ring. By analogy, benzoxazole has a benzene ring fused to oxazole Benzimidazole Benzoxazole Similarly, benzothiazole has a benzene ring fused to thiazole Benzothiazole Back Forward Main Menu TOC Study Guide Toc Student OLC MHHE Website
11.16 Resonance structures are generated for cyclopentadienide anion by moving the unshared electron pair from the carbon to which it is attached to a position where it becomes a shared electron pair in a bond. 11.17 The process is an acid–base reaction in which cyclopentadiene transfers a proton to amide ion (the base) to give the aromatic cyclopentadienide anion. The sodium ion (Na) has been omitted from the equation. 11.18 (b) Cyclononatetraenide anion has 10 electrons; it is aromatic. The 10 electrons are most easily seen by writing a Lewis structure for the anion: there are 2 electrons for each of four double bonds, and the negatively charged carbon contributes 2. 11.19 Indole is more stable than isoindole. Although the bonding patterns in both five-membered rings are the same, the six-membered ring in indole has a pattern of bonds identical to benzene and so is highly stabilized. The six-membered ring in isoindole is not of the benzene type. 11.20 The prefix benz- in benzimidazole (structure given in text) signifies that a benzene ring is fused to an imidazole ring. By analogy, benzoxazole has a benzene ring fused to oxazole. Similarly, benzothiazole has a benzene ring fused to thiazole. S N Benzothiazole N H N Benzimidazole O N Benzoxazole N H Indole more stable NH Isoindole less stable Six-membered ring corresponds to benzene. Six-membered ring does not have same pattern of bonds as benzene. H H NH2 H NH3 1,3-Cyclopentadiene Amide ion Cyclopentadienide anion Ammonia H H H H H H H H H H H H H H H H H H H H H H H H H 258 ARENES AND AROMATICITY Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website
ARENES AND ARO 259 11.21 Write structural formulas for the species formed when a proton is transferred to either of the two nitrogens of imidazole Protonation ofn-1 The species formed on protonation of N-1 is not aromatic. The electron pair of N-l that contributes to the aromatic 6 T-electron system of imidazole is no longer available for this purpose because it used to form a covalent bond to the proton in the conjugate acid. Protonation of N-3 H The species formed on protonation of N-3 is aromatic. Electron delocalization represented by the resonance forms shown allows the 6 T-electron aromatic system of imidazole to be retained in its conjugate acid. The positive charge is shared equally by both nitrogens H 11.22 Since the problem requires that the benzene ring be monosubstituted, all that needs to be examined are the various isomeric forms of the C4H, substituent. CH,CH,,CH3 CHCHCH (l-phenylbutane) (2-phenylbutane) C CH,CH(CH3) Isobutylbenzene tert-Butylbenzene (2-methyl-l-phenylpropane) (2-methyl-2-phenylpropane) These are the four constitutional isomers. sec-Butylbenzene is chiral and so exists in enantiomeric R and s forms 11.23 (a) An allyl substituent is-CH, CH=CH2 CHCHECH Allylbenzene Back Forward Main Menu TOC Study Guide Toc Student OLC MHHE Website
11.21 Write structural formulas for the species formed when a proton is transferred to either of the two nitrogens of imidazole. Protonation of N-1: The species formed on protonation of N-1 is not aromatic. The electron pair of N-1 that contributes to the aromatic 6 -electron system of imidazole is no longer available for this purpose because it is used to form a covalent bond to the proton in the conjugate acid. Protonation of N-3: The species formed on protonation of N-3 is aromatic. Electron delocalization represented by the resonance forms shown allows the 6 -electron aromatic system of imidazole to be retained in its conjugate acid. The positive charge is shared equally by both nitrogens. 11.22 Since the problem requires that the benzene ring be monosubstituted, all that needs to be examined are the various isomeric forms of the C4H9 substituent. These are the four constitutional isomers. sec-Butylbenzene is chiral and so exists in enantiomeric R and S forms. 11.23 (a) An allyl substituent is @CH2CH?CH2. Allylbenzene CH2CH CH2 Butylbenzene (1-phenylbutane) CH2CH2CH2CH3 sec-Butylbenzene (2-phenylbutane) CHCH2CH3 CH3 Isobutylbenzene (2-methyl-1-phenylpropane) CH2CH(CH3)2 tert-Butylbenzene (2-methyl-2-phenylpropane) C(CH3)3 H H N N N N H H H3O N N H 3 1 H H N N 3 1 H3O N N H 1 N N H H 3 3 1 ARENES AND AROMATICITY 259 Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website
260 ARENES AND AROMATICITY (b) The constitution of l-phenyl-1-butene is C6HS CH=CHCH, CH3. The E stereoisomer is H CHCH The two higher ranked substituents, phenyl and ethyl, are on opposite sides of the double bond (c) The constitution of 2-phenyl-2-butene is CH, C=CHCH, The Z stereoisomer is C6H5 H,C (Z)-2-Phenyl-2-butene The two higher ranked substituents, phenyl and methyl, are on the same side of the double bond (d) 1-Phenylethanol is chiral and has the constitution CH_ CHC6Hs. Among the substituents attached to the stereogenic center, the order of decreasing precedence is HO >CHs>CH3>H In the R enantiomer the three highest ranked substituents must appear in a clockwise sense in proceeding from higher ranked to next lower ranked when the lowest ranked substituent is di- rected away from you (R)-1-Phenylethanol (e) A benzyl group is CHs CH2. Benzyl alcohol is therefore CBH_ CH,OH and o-chlorobenzyl alcohol is -CH-OH (f) In p-chlorophenol the benzene ring bears a chlorine and a hydroxyl substituent in a 1, 4 (g) Benzenecarboxylic acid is an alternative IuPAC name for benzoic acid CO,H 2-Nitrobenzenecarboxylic acid Back Forward Main Menu TOC Study Guide Toc Student OLC MHHE Website
(b) The constitution of 1-phenyl-1-butene is C6H5CH?CHCH2CH3. The E stereoisomer is The two higher ranked substituents, phenyl and ethyl, are on opposite sides of the double bond. (c) The constitution of 2-phenyl-2-butene is . The Z stereoisomer is The two higher ranked substituents, phenyl and methyl, are on the same side of the double bond. (d) 1-Phenylethanol is chiral and has the constitution . Among the substituents attached to the stereogenic center, the order of decreasing precedence is HO C6H5 CH3 H In the R enantiomer the three highest ranked substituents must appear in a clockwise sense in proceeding from higher ranked to next lower ranked when the lowest ranked substituent is directed away from you. (e) A benzyl group is C6H5CH2@. Benzyl alcohol is therefore C6H5CH2OH and o-chlorobenzyl alcohol is ( f ) In p-chlorophenol the benzene ring bears a chlorine and a hydroxyl substituent in a 1,4- substitution pattern. (g) Benzenecarboxylic acid is an alternative IUPAC name for benzoic acid. CO2H NO2 2-Nitrobenzenecarboxylic acid OH Cl p-Chlorophenol CH2OH Cl H3C C OH H (R)-1-Phenylethanol OH CH3CHC6H5 (Z)-2-Phenyl-2-butene H C C CH3 H3C CH3C C6H5 CHCH3 (E)-1-Phenyl-1-butene CH2CH3 C C H H 260 ARENES AND AROMATICITY Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website
ARENES AND ARO 261 (h) Two isopropyl groups are in a 1, 4 relationship in p-disopropylbenzene CH(CH3)2 CH(CH3)2 (i) Aniline is CSHSNH, Therefore NH 2.4.6-Tribromoaniline G Acetophenone(from text Table Il. 1)is C6H-CCH3 Therefore C () Styrene is CH CH=CH, and numbering of the ring begins at the carbon that bears the side chain CHCH 4-Bromo-3-ethylstyrene 11.24 (a) Anisole is the name for CH_OCH,, and allyl is an acceptable name for the group HIC=CHCH2-. Number the ring beginning with the carbon that bears the methoxy group (b) Phenol is the name for CHsOH. The ring is numbered beginning at the carbon that bears the hydroxyl group, and the substituents are listed in alphabetical order (c) Aniline is the name given to CHSNH,. This compound is named as a dimethyl derivative of aniline Number the ring sequentially beginning with the carbon that bears the amino group OCH NH C CH CH,CH=CH, Estragole 4-Allvlanisole 2,6-D.Diosphenol m-Xylidine Back Forward Main Menu TOC Study Guide Toc Student OLC MHHE Website
(h) Two isopropyl groups are in a 1,4 relationship in p-diisopropylbenzene. (i) Aniline is C6H5NH2. Therefore (j) Acetophenone (from text Table 11.1) is . Therefore (k) Styrene is and numbering of the ring begins at the carbon that bears the side chain. 11.24 (a) Anisole is the name for C6H5OCH3, and allyl is an acceptable name for the group . Number the ring beginning with the carbon that bears the methoxy group. (b) Phenol is the name for C6H5OH. The ring is numbered beginning at the carbon that bears the hydroxyl group, and the substituents are listed in alphabetical order. (c) Aniline is the name given to C6H5NH2. This compound is named as a dimethyl derivative of aniline. Number the ring sequentially beginning with the carbon that bears the amino group. OCH3 CH2CH CH2 1 6 2 5 3 4 Estragole 4-Allylanisole OH I I NO2 1 6 2 5 3 4 Diosphenol 2,6-Diiodo-4-nitrophenol NH2 H3C CH3 1 6 2 5 3 4 m-Xylidine 2,6-Dimethylaniline H2C CHCH2 CH3CH2 Br CH CH2 3 4 1 5 6 2 4-Bromo-3-ethylstyrene C6H5CH CH2 C H3C NO2 O m-Nitroacetophenone C6H5CCH3 O NH2 Br Br Br 2,4,6-Tribromoaniline p-Diisopropylbenzene CH(CH3)2 CH(CH3)2 ARENES AND AROMATICITY 261 Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website
262 ARENES AND AROMATICITY 11.25(a) There are three isomeric nitrotoluenes, because the nitro group can be ortho, meta, or para to the methyl group CH trotoluen m-Nitrotoluene p-Nitrotoluene (b) Benzoic acid is CH CO, H. In the isomeric dichlorobenzoic acids, two of the ring hydrogens of benzoic acid have been replaced by chlorines. The isomeric dichlorobenzoic acids are COH COH COH Cl Cl 2.3-Dichlorobenzoic 2, 4-Dichlorobenzoic 2. 5-Dichlorobenzoic COH CO,H COH 2. 6-Dichlorobenzoic 3, 4-Dichlorobenzoic 3.5-Dichlorobenzoic The prefixes o-, m-, and p- may not be used in trisubstituted arenes; numerical prefixes are used. Note also that benzenecarboxylic may be used in place of benzoic. (c) In the various tribromophenols, we are dealing with tetrasubstitution on a benzene rin Again, o-m-and p-are not valid prefixes. The hydroxyl group is assigned position 1 because the base name is phenol. OH 2.3.4-Tb 2,.5-Tribromophen 2.3, 6-Tribromophenol OH B1 Br 2,4,5-Tribromophenol 2, 4, 6-Tribromophenol 3, 4-5-Tribromophenol Back Forward Main Menu TOC Study Guide Toc Student OLC MHHE Website
11.25 (a) There are three isomeric nitrotoluenes, because the nitro group can be ortho, meta, or para to the methyl group. (b) Benzoic acid is C6H5CO2H. In the isomeric dichlorobenzoic acids, two of the ring hydrogens of benzoic acid have been replaced by chlorines. The isomeric dichlorobenzoic acids are The prefixes o-, m-, and p- may not be used in trisubstituted arenes; numerical prefixes are used. Note also that benzenecarboxylic may be used in place of benzoic. (c) In the various tribromophenols, we are dealing with tetrasubstitution on a benzene ring. Again, o-, m-, and p- are not valid prefixes. The hydroxyl group is assigned position 1 because the base name is phenol. 2,4,5-Tribromophenol OH Br Br Br 2,4,6-Tribromophenol Br Br OH Br 3,4,5-Tribromophenol Br Br OH Br 2,3,4-Tribromophenol OH Br Br Br 2,3,5-Tribromophenol Br OH Br Br 2,3,6-Tribromophenol Br Br OH Br Cl Cl CO2H 2,6-Dichlorobenzoic acid 3,4-Dichlorobenzoic acid CO2H Cl Cl 3,5-Dichlorobenzoic acid CO2H Cl Cl 2,3-Dichlorobenzoic acid CO2H Cl Cl 2,4-Dichlorobenzoic acid CO2H Cl Cl 2,5-Dichlorobenzoic acid CO2H Cl Cl CH3 NO2 o-Nitrotoluene (2-nitrotoluene) CH3 NO2 p-Nitrotoluene (4-nitrotoluene) m-Nitrotoluene (3-nitrotoluene) CH3 NO2 262 ARENES AND AROMATICITY Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website
