2-substituted thiophene compounds with electron donating and electron withdrawing p-phenyl substitution were synthesized and studied their radical scavenging properties using DPPH assay and DFT method. It is shown that p-hydroxy and p-amino phenyl substituted compound exhibit radical scavenging activity. From DFT and radical scavenging studies, a correlation between IC₅₀ with the bond dissociation enthalpy, proton affinity, ground state dipole moment and optical band gap of compound is found. Compounds 1–3 with electron withdrawing substituent (NO₂, CN, Cl) do not show any radical scavenging properties, whereas compounds 6–7 with electron donating substituent (OH, NH₂) show antiradical properties. Further, the antiradical activity is reduced drastically by replacing the -OH and -NH₂ with methoxy and -N-alkylating group respectively in 6 and 7. The compound with p-hydroxy phenyl substitution, exhibits stronger antiradical activity as compared to the p-amino phenyl substitution due to smaller O-H bond dissociation energy as compared to the N-H bond. From DPPH and DFT studies, it is suggested that the radical scavenging activity in 2-substituted thiophene is occurred through proton transfer mechanism. The other possible SET, SPLET mechanisms are also corroborated.

合成了具有给电子和吸电子对位苯基取代基的2-取代噻吩化合物，并通过DPPH法和DFT法研究了它们的自由基清除性能。结果表明，对羟基和对氨基苯基取代的化合物表现出自由基清除活性。通过DFT和自由基清除研究，发现IC ₅₀与化合物的键解离焓，质子亲和力，基态偶极矩和光学带隙之间存在相关性。化合物1 - 3与吸电子取代基（NO ₂，CN，Cl）的不显示任何自由基清除性能，而化合物6 -7与供电子取代基（OH，NH ₂）示出的抗自由基性。此外，通过分别在6和7中用甲氧基和-N-烷基化基团取代-OH和-NH ₂，大大降低了抗自由基活性。与对-p-相比，具有对-羟基苯基取代的化合物表现出更强的抗自由基活性。与NH键相比，由于OH键的离解能较小，所以可以进行氨基苯基取代。从DPPH和DFT研究表明，2-取代噻吩的自由基清除活性是通过质子转移机理发生的。其他可能的SET，SPLET机制也得到了证实。