Aniline Annulenes

Electrostatic potential map—cont d ammonia, 145 aniline, 925 anilinium ion, 925 anisole, 111 18]annulene, 535 arene, 74 azulene, 541 benzaldehyde, 565, 704 benzene, 44, 521, 565 benzenediazonium ion, 945 benzoquinone, 631 benzyl carbocation, 377 benzyne, 576 borane, 223... 

ANILINES 4-Chloro-2-pbenylquliiazolme. ANNULENES Propaigyl aldehyde. ANTHRONES Pyiidene hydrochloride. APORPHINES 6-Methoxy-7-hydroxy-3,4-dihydroisoquinoliniuin methiodide. ARYLACETIC ACIDS Ceric acetate. ARYLACETYLENES n-Butylamine. Iodoethynyl(trimethyl)siIane. 

It suggests that it is not the size of the ring but the number of electrons present in it determines whether a molecule would be aromatic or antiaromatic. In fact the molecules with An+ 2) n electrons are aromatic whereas with (An, 0) n electrons are antiaromatic. Thus, benzene, cyclopropenyl cation, cyclobutadiene dication (or dianion), cyclopentadie-nyl anion, tropylium ion, cyclooctatetraene dication (or dianion), etc. possess (4 + 2) ti electrons and hence aromatic whereas cyclobutadiene, cyclopentadienyl cation, cycloheptatrienyl anion, cyclooctatetraene (non-planar) etc. have An n electrons which make them antiaromatic . Systems like [10] annulene are forced to adopt a nonplanar conformation due to transannular interaction between two hydrogen atoms and hence their aromaticity gets reduced even if they have (An + 2)n electrons. On the other hand the steric constraints in systems like cyclooctatetraene force it to adopt a tube-like non-planar conformation which in turn reduces its antiaromaticity. Various derivatives of benzene like phenol, toluene, aniline, nitrobenzene etc. are also aromatic where the benzene ring and the n sextet are preserved. In homoaromatic " systems, like cyclooctatrienyl cation, delocalization does not extend over the whole molecule. 

Aroma2 Rule C-replaced benzenoids are more aromatic than substituted benzenoids, e.g.. Pyridine and Pyiimidine vs. Phenol and Aniline ordering aromaticity in Table 4.5 this rule extends the substituted versus addition rules in aromaticity historical definition (see Introduction) AromaS Rule double-C-replaced annulens have greater aromaticity than mono-C-replaced annulenes, e.g., this is... 

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