Abstract A study of orientation effect of the phenyl(RPh) on the electrophilic aromatic substitution in the biphenyls (RPh-Ph,R:NH2,CH3,OH,Br,H,CHO,CN,COOH,NO2) was carried out by the G03 packages software at HF/6 -31G basis set level, respectively. The conformational analysis of the biphenyl and substituted biphenyls showed that the rotational barrier about the carbon-carbon bond in biphenyl and m, p-substituted biphenyls is tiny, the rotation energy barrier (△E) is ca. 12 kJ/mol, the rotational barrier △E(R) in o-substituted biphenyl is larger than biphenyl and m, p-substituted biphenyls, △E(COOH) > △E(NO2) > △E(CHO) > △E(CH3) > △E(NH2) > △E(OH) > △E(Br) > △E(CN), as a result, their rotation about the carbon-carbon bond is sterically hindered. The atomic charge distribution of the biphenyl and substituted biphenyls with the conformational is change. The minimum energy structure of biphenyls in same compound, whether this substituent group (R) is the class Ⅰ or the class Ⅱ positioning group, it is larger total charge density on the unsubstituted benzene ring of carbon atoms than substituted benzene ring, the electrophilic substitution reaction, therefore, introduction of a second substituent usually selective takes place in the unsubstituted benzene ring.Due to the charge density of o-carbon atoms of unsubstituted benzene is relatively small, and stereo effect is larger, and the charge density of p-carbon atoms is larger, introduction of a second substituent usually selective takes place in the unsubstituted benzene ring in the p-position.Therefore, substituted phenyl (RPh) is p-positioning group in the biphenyls.
KUANG Dai-Zhi, ZHANG Fu-Xing, FENG Yong-Lan, XU Zhi-Feng, JIANG Wu-Jiu. Orientation Effect of Phenyl on Electrophilic Electrophilic Substitution in Biphenyl[J]. Chinese Journal of Chemical Education, 2017, 38(22): 73-80.
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