A Study On The Aromaticity Of Carbaporphyrins

Aromaticity is one of the most important concepts in organic chemistry.Many criteria for determining aromaticity have been advanced.These are based on acompound’s molecular properties and have generally been divided into four categories:structural,magnetic,energetic,and electronic.Porphyrin and related compounds aredistributed widely in nature and are found in many important natural substances such as heme,chlorophyll,and Vitamin B12.Therefore the study of porphyrins hasattracted great interest for many years.Porphyrin compounds are a type of largeπ-conjugated molecules in which four pyrrole rings are connected by methine bridges.Carbaporphyrins are porphyrin analogues in which one or more of the pyrrolicnitrogen atoms have been replaced by a carbon atom.In this paper,we use the TRE and%TRE methods,which belong to the energetic criterion of aromaticity,to study the global aromaticity of carbaporphyrins,heterodiazuliporphyrins,o-dicarbaporphyrins,benzoporphyrins,dibenzoporphyrins,and tribenzoporphyrins.The local aromaticity of these compounds was analyzedusing the BRE and CRE methods.Our BRE and CRE results are compared with the results obtained by the use of other criteria of aromaticity as reported in the literature.The RC intensity of the compounds is predicted by the Hückel-London method.The correlation between the observed ~1H NMR chemical shift and our RC results isdiscussed.This thesis consists of six chapters,each of which is outlined below.In the first chapter,the origin,development,and the characteristics of thedifferent criteria of aromaticity are introduced.In addition,the research methods used in this paper are described.In the second chapter,we analyze the global aromaticity of carbaporphyrins using the TRE and%TRE methods.The relative aromaticity of these compounds is explained using the TCS rule.The local aromaticity of these compounds is studied using the BRE and CRE methods and is compared with the NICS results as reported in the literature.Finally,the RC intensity of carbaporphyrins is predicted using the RC method,and the relationship between the RC results and the observed ~1H-NMR chemical shifts is discussed.In the third chapter,the global aromaticity of diheterodiazuliporphyrins,both in the neutral and the dicationic states,is investigated using the TRE method.Their local aromaticity is determined using the BRE and CRE indices.The main conjugationpathways are identified using the BRE and CRE indices.The correlation between the observed ~1H NMR chemical shift and the ring current strength is discussed.Thestrength of the magnetically induced RC is calculated using the Hückel-London model.The correlation between the observed ~1H NMR chemical shift and the RC strength is discussed and good correlation was obtained.Finally,the main impact factors upon aromaticity and RCs are clarified.In the forth chapter,the global aromaticity of o-dicarbaporphyrins and their dications is investigated using the TRE and%TRE methods.Their local aromaticity is predicted using the BRE and CRE indices.The strength of the magnetically induced RC is calculated using the Hückel-London model.In the fifth chapter,the global aromaticity of benzocarbaporphyrins and dibenzo carbaporphyrins is studied by the use of the TRE and%TRE methods.The relative aromaticity of these compounds is explained using the TCS rule.The local aromaticity of these compounds is studied using the BRE and CRE methods and is compared with the NICS results reported in the literature.The main conjugation pathways are identified using the BRE and CRE indices.Finally,the correlation between the observed ~1H NMR chemical shift and the RC strength is discussed and good correlation was obtained.In the sixth chapter,the global aromaticity of tribenzocarbaporphyrins is examined using the TRE and%TRE methods.The relative aromaticity of these compounds is explained by the use of the TCS rule.The local aromaticity of these compounds is studied using the BRE and CRE methods,and their magnetic properties are predicted using the Hückel-London model.