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1、HeterocyclicCompoundsAssoc.prof.LubomirMakedonski,PhDMedicalUniversityofVarnaOtherelementssuchasnitrogenandoxygencanbeincludedintherings.Whentheyare,thecompoundsarecalledheterocycliccompounds.Thehetero-partofthenamemeansthatmorethanonekindofelementisincludedwithintheringand-cyclic,ofcourse,indica
2、testhatthereisatleastoneringpresentinthecompound.Compoundsclassifiedasheterocyclicprobablyconstitutethelargestandmostvariedfamilyoforganiccompounds.Afterall,everycarbocycliccompound,regardlessofstructureandfunctionality,mayinprinciplebeconvertedintoacollectionofheterocyclicanalogsbyreplacingoneor
3、moreoftheringcarbonatomswithadifferentelement.Evenifwerestrictourconsiderationtooxygen,nitrogenandsulfur(themostcommonheterocyclicelements),thepermutationsandcombinationsofsuchareplacementarenumerous.SomeimportantheterocycliccompoundswithN-heteroatomPyrrolIndolePyridinePyrazoleImidazole27Pyramidi
4、nePurineNomenclatureDevisingasystematicnomenclaturesystemforheterocycliccompoundspresentedaformidablechallenge,whichhasnotbeenuniformlyconcluded.Manyheterocycles,especiallyamines,wereidentifiedearlyon,andreceivedtrivialnameswhicharestillpreferred.Aneasytoremember,butlimited,nomenclaturesystemmake
5、suseofanelementalprefixfortheheteroatomfollowedbytheappropriatecarbocyclicname.Ashortlistofsomecommonprefixesisgiveninthefollowingtable.Examplesofthisnomenclatureare:§ethyleneoxide=oxacyclopropane§furan=oxacyclopenta-2,4-diene§pyridine=azabenzene§morpholine=1-oxa-4-azacyclohexane.Elementoxygensul
6、furseleniumnitrogenphosphoroussiliconboronValenceIIIIIIIIIIIIIVIIIPrefixOxaThiaSelenaAzaPhosphaSilaBora27Allthepreviousexampleshavebeenmonocycliccompounds.Polycycliccompoundsincorporatingoneormoreheterocyclicringsarewellknown.Afewoftheseareshowninthefollowingdiagram.Thus,thelocationofafusedringma
7、ybeindicatedbyalowercaseletterwhichdesignatestheedgeoftheheterocyclicringinvolvedinthefusion,asshownbythepyridineringinthegreenshadedbox.Heterocyclicringsarefoundinmanynaturallyoccuringcompounds.Mostnotably,theycompose
