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Toluene has a $\ce{CH3}$ group attached to the benzene ring and as a result due to the +I effect of $\ce{CH3}$, the electron density in the ring increases and it undergoes nitration faster than a normal benzene ring.
But what causes thiophene to have an even greater rate of nitration ?

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I would suggest two reasons:

  1. Thiophene is an electron-rich compound because of presence of two lone pairs on the sulphur atom. Hence, it attracts electrophiles readily.

  2. Though its aromaticity is lesser than that of benzene, the delocalisation is among five atoms in thiophene whereas in benzene it is among six atoms. Hence electron density in thiophene is more.

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  • $\begingroup$ I am not sure if this answer is correct. (1) Yes sulphur has lone "pairs", but only one of them is involved in resonance with the ring (the other is out of the place of the ring) (2) sulphur's 3p orbitals have weaker overlap than that of carbon's 2p orbitals with the ring (3) you seem to be comparing thiophene with benzene instead of toluene (as asked by OP), and have completely ignored the hyperconjugative increase in electron density (due to the methyl group in toluene which is absent in thiophene) $\endgroup$ – Gaurang Tandon Mar 2 '18 at 12:21
  • $\begingroup$ Yes, (3) I didnt notice toluene, my bad. (2) I don’t get why. (1) is again a drawback. My bad! Just realised how poor my answer is. Can you explain me (2)? And should i remove the answer? $\endgroup$ – MollyCooL Mar 2 '18 at 16:59
  • $\begingroup$ (2) same size $\ce{2p\pi-2p\pi}$ overlap is better than different size $\ce{3p\pi-2p\pi}$. "And should i remove the answer?" I am not sure what to do in this case. Lemme think. $\endgroup$ – Gaurang Tandon Mar 2 '18 at 17:07
  • $\begingroup$ I think you should remove it. It's going to be misguiding for other visitors. No offence but please remove. $\endgroup$ – Archer Mar 25 '18 at 23:38
  • $\begingroup$ It says I can’t delete an accepted answer :( $\endgroup$ – MollyCooL Mar 26 '18 at 10:54

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