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 Website11.16 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