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 Website11.21 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