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Usually when an ortho-para directing substituent is present on the benzene ring for an electrophilic aromatic substitution reaction, the para product is the major product (exceptions can be there when hydrogen bonding or ortho effect of COOH group makes the ortho product a major one.) But I don't understand why the ortho product in nitration of toluene is the major product (and the para product isn't). The ortho position is supposed to have more steric crowding, right?

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  • $\begingroup$ Now I know nothing about this particular nitration but one thing that tends to make ortho products favorable is the inductive effect, due to which ortho position of toulene is slightly more activated than para. $\endgroup$ – Sawarnik Apr 9 '17 at 18:49
  • $\begingroup$ i read the answers and now I'm confused . If this is the reason then what if there is an ethyl group instead of methyl . Ortho position should be major because of +I effect but this is not the case as para is major .why is that $\endgroup$ – utkarsh Apr 10 '17 at 12:19
  • $\begingroup$ @utkarsh Then steric hindrance increases and the nitro group will go to the para position. $\endgroup$ – dr.drizzy Mar 2 '18 at 20:29
  • $\begingroup$ Related: chemistry.stackexchange.com/questions/88752/… $\endgroup$ – Avnish Kabaj Mar 3 '18 at 3:43
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  1. A methyl-group is not t-butyl, so it isn't all that crowded.
  2. There are two ortho-positions.
  3. There is also the possibility of an ipso-attack with the nitronium donor attacking the position of the methyl group, then shifting to the ortho-position.

Given all that without any orientation effect, the ratio between ortho and para should be around 3/1 - 2/1. It is commonly observed around 3/2, so the crowding does have an effect.

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There are three effects: sterics, electronics and statistics.

Yes, there is more steric crowding in the ortho position, but a methyl group isn't that big. In addition, electronic effects are stronger in ortho position than in para, since it is much closer to the +I substituent. And last but not least: there are two ortho positions which can react, but only one para-position, which can have a rather big influence if reactivity towards ortho and para position is similar.

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