Synthesis Of 2-(4-Substituted Phenyl)-5-Substituted Pyrimidines And Effect Of Substituents On Chemical Shift Of Nuclear Magnetic Resonance,Ultraviolet Spectra And Reduction Potential

Pyrimidine derivatives,an important class of heterocyclic compounds based on pyrimidine rings,are widely used in pharmaceutical,agricultural and optoelectronic materials and other related fields for having a wide range of physiological and pharmacological activities such as anti-cancer,anti-inflammatory,insecticidal,bactericidal,and herbicidal activities,as well as excellent optical and electrical properties.Substituents have an important influence on the properties of pyrimidine derivatives.In our previous work,the substituent effects on the physico-chemical properties of 2-X-5-Y pyrimidines have been systematically studied.Many pyrimidine derivatives,contain a conjugated system with various aromatic rings.Especially for the photoelectric materials with pyrimidine ring,there are generally a long conjugation chain consisting of pyrimidine rings and benzene rings.In this dissertation,a series of 2-（4-X-phenyl）-5-Y pyrimidines were synthesized,where the conjugated chain was extended by attaching a benzene ring to the 2-position carbon of pyrimidine ring.In this series of compounds,one substituent Y is attached to a polar pyrimidine ring,and the other substituent X is connected to a non-polar benzene ring.How do these two substituents X and Y affect the properties of compounds?What are the similarities and differences between the rule and the influence X and Y pair substituents on 2-X-5-Y pyrimidines?And the following research develops in order to address this issue.48 2-（4-X-phenyl）-5-Y pyrimidines were designed and synthesized（substituents X,Y=NMe2,OCH3,NH2,OH,CH3,H,Cl,Br,I,CN,NO2,CF3）.The structures of compounds were characterized by Nuclear Magnetic Resonance spectra of ¹H and ¹³C(¹H NMR and ¹³C NMR).The UV spectra and reduction potentials of these compounds were also recorded.Quantitative structure-property relationship were investigated against the NMR chemical shifts（δ）,the maximum wavenumber(ν_max)of ultraviolet absorption and the reduction potential（ERed）.The conclusions were obtained as follows.（1）In order to characterize the structure of substituents,the following structural parameters were considered:Hammett parametersσ（σ_F andσ_R）,excited-state substituent effect parameters(σ_CC^ex),electronegativity parameters（χ）,and indicator variable（D）characterizing the heavy atom effect.（2）¹³C NMR chemical shiftsδ（C₂）、δ(C_4,6)、δ（C₅）、δ(C_1’)、δ(C_4’)of C₂,C₄（same as C₆）,C₅ on pyrimidine ring and C_1’,C_4’on benzene rings,the ¹H NMR chemical shiftδ(H_4,6)of H_4,6,6 on pyrimidine ring were all characterized.Quantitative structure-property relationship studies have shown that:The influences of substituents X and Y on the chemical shifts at different positions are various Not onlyδ(H_4,6)andδ（C₅）on the pyrimidine ring,but alsoδ(C_1’)and(C_4’)on the benzene ring are greatly influenced by the proximal substituent（Y/X）,while the influence by the distal substituent is smaller.（3）Quantitative structure-property relationship model was also built for the maxium absorption wavenumber(ν_max)corresponding to the maxium absorption wavelength(λ_max)of ultraviolet absorption of model compounds.It is indicated that theν_max of2-（4-X-phenyl）-5-Y pyrimidine is mainly affected by the conjugative effect and excited-state substituent effect of the 4-X on the benzene ring,the conjugative effect and excited-state substituent effect of 5-Y on the pyrimidine ring,together with the cross interactions between substituents X and Y.（4）Quantitative structure-property relationship investigation against reduction potential(E_Red)revealed that the conjugative effects,indicator variable for the heavy atom effect of both substituents X and Y,the cross interaction between substituents X and Y,and the electronegativity parameter of substituent Yare all responsible for the reduction potential of2-（4-substituted phenyl）-5-Y pyrimidine.（5）Comparing the substituent effects of 2-（4-X-phenyl）-5-Y pyrimidines to those of2-X-5-Y pyrimidines,it was found that the substituent effects of two series of compounds were different.Furthermore,the distinctions varied for different properties.These investigations indicated that the substituents on different parent skeletons had different effects on the properties of compounds,which confirmed that the substituent effect is not only related to the nature of substituent,but also closely related to the parent skeleton structure.