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Reactions of Aromatic Molecules

By James Ashenhurst

Ortho-, Para- and Meta- Directors in Electrophilic Aromatic Substitution

Last updated: October 24th, 2024 |

Two Important Reaction Patterns: Ortho- , Para- Directors and Meta- Directors

It’s one thing to learn about electrophilic aromatic substitution reactions of benzene itself.

But once you move toward substituted benzenes, that’s when things start getting really interesting.

Today we’ll describe the two main patterns by which various substituents “direct” electrophilic aromatic substitution.

  • In one pattern, substituents direct the reaction to give either the “ortho” (1,2) or “para” product, with a slight preference for “para” (1,4).
  • In the second pattern, a different family of substituents direct the reaction to give primarily the “meta” (1,3) product.

summary-ortho meta para directors for electrophilic aromatic substitution

Table of Contents

  1.  ortho-, para- Directors
  2. meta- Directors
  3. How Well Do “ortho-, para” And “meta“- Directors Correlate With “Activating” and “Deactivating” Groups?
  4. The Key To Understanding ortho-, para- Directors And meta- Directors Is To Understand The Stability of The Carbocation Intermediate
  5. Notes
  6. Quiz Yourself!

1. ortho-, para- Directors

Here’s a fascinating observation.

Start with a monosubstituted benzene. Then perform some kind of electrophilic aromatic substitution  (nitration, halogenation, sulfonation – turns out it doesn’t matter).

Two important reaction patterns are observed. 

It’s important to note that these two patterns are wholly a function of the substituent and not the reaction itself.

In one pattern, ortho- and para– products dominate, and the meta- product is an extremely minor byproduct.

what is an ortho para director - gives mostly ortho and para products in electrophilic aromatic substitution with examples

Substituents which lead to this result are called, “ortho-, para- directors”. Examples of ortho-, para– directors are hydroxyl groups, ethers, amines, alkyl groups, thiols, and halogens.

Here’s a concrete example: the nitration of methoxybenzene (also known as anisole).

electrophilic aromatic substitution of anisole showing it to be ortho para director example

ortho- and para- products dominate, while meta– products comprise less than 3%.

2. meta- Directors

In the second pattern, the meta– product dominates, and the ortho- and para– products are minor.

what is a meta director - substituent which gives mostly meta product in electrophilic aromatic substitution with example

We call the substituents which lead to this result “meta- directors”. Examples of meta– directors include nitriles, carbonyl compounds (such as aldehydes, ketones, and esters), sulfones, electron-deficient alkyl groups, nitro groups, and alkylammoniums.

Specific example: nitration of trifluoromethylbenzene gives the meta product in about 90% yield. (Compare that to the case of anisole, above, where nitration resulted in a <5% yield of the meta product. )

electrophilic aromatic substitution of trifluoromethylbenzene gives mostly meta products

3. How Well Do “ortho-, para” And “meta“- Directors Correlate With “Activating” and “Deactivating” Groups

What factors could be in play here? How do ortho-, para- and meta– directors differ, and how could this difference affect the product distribution?

Great question.

One aspect we’ve covered previously is the concept of “activating” and “deactivating” groups.

We said that

  • Activating groups increase the rate of electrophilic aromatic substitution, relative to hydrogen.
  • Deactivating groups decrease the rate of electrophilic aromatic substitution, relative to hydrogen.

If you look through the list of ortho- , para- directors, you might recognize that many of them are also activating groups.

Likewise, the list of meta- directors (nitro, CF3, cyano) is like a who’s who of deactivating groups.

If you’re a real nerd, you could even make a 2 × 2 matrix, like this:

table of activating deactivating ortho para meta directors matrix

What do we notice?

  • First: no activating groups are meta directors.
  • Second: what’s up with the halogens?

Yes indeed. What is up with the halogens, and how is it that they can be deactivating (i.e. slow down the reaction rate) and yet lead to ortho-, para- products?

4. The Key To Understanding ortho-, para- Directors And meta- Directors Is To Understand The Stability of The Carbocation Intermediate

There’s no quick and thorough answer to these questions, and it’s worth its own separate article for that reason.

However, the first place to start is that it has to do with the stability of the carbocation intermediate in electrophilic aromatic substitution reactions. [See this previous post on the mechanism of electrophilic aromatic substitution].  More specifically, how does each substituent affect the stability of that intermediate?

It might be worth going back and revisiting some of the factors that affect the stability of carbocations.

And also, if you prefer to look at it from the opposite side of the coin, here are some of the factors which make carbocations more unstable.

In our next post, we’ll explain the reasons for both ortho-, para- and meta- direction, and try to show why halogens fit in the former category but not the latter.

Next Post: Understanding Ortho, Meta, and Para Directors

Notes

Related Articles

Quiz Yourself!

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00 General Chemistry Review
01 Bonding, Structure, and Resonance
02 Acid Base Reactions
03 Alkanes and Nomenclature
04 Conformations and Cycloalkanes
05 A Primer On Organic Reactions
06 Free Radical Reactions
07 Stereochemistry and Chirality
08 Substitution Reactions
09 Elimination Reactions
10 Rearrangements
11 SN1/SN2/E1/E2 Decision
12 Alkene Reactions
13 Alkyne Reactions
14 Alcohols, Epoxides and Ethers
15 Organometallics
16 Spectroscopy
17 Dienes and MO Theory
18 Aromaticity
19 Reactions of Aromatic Molecules
20 Aldehydes and Ketones
21 Carboxylic Acid Derivatives
22 Enols and Enolates
23 Amines
24 Carbohydrates
25 Fun and Miscellaneous
26 Organic Chemistry Tips and Tricks
27 Case Studies of Successful O-Chem Students

Comments

Comment section

47 thoughts on “Ortho-, Para- and Meta- Directors in Electrophilic Aromatic Substitution”

  1. If ortho/para directors and meta directors are together in a reactant molecule, after substitution reaction, what products appear?

    Reply
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    1. Let’s say you did 4 different electrophilic aromatic substitution reactions (e.g. nitration) with PhCl, PhNO2, PhCF3, and PhCN. You measure the rates. All all slower than benzene. Of the four, one is fastest and one is slowest. You’d probably call the one that is the fastest, “weakly deactivating” and the one that is the slowest, “strongly deactivating”, and the ones in the middle, “moderately deactivating”.

      Reply

  6. How to determine where to add when there are two ortho para directing group for eg in
    3 methyl phenol nitration->???

    Reply
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  10. Hey, I had a doubt. When we have phenol substituted with no2 which is an electron withdrawing group. Which one will be more acidic, ortho nitro phenol or para nitro phenol?

    Reply

  11. that is really a wonderful article but something confuses me that what is the trend of halogens when they behave as deactivating ortho para directors which halogen is most de activating and which is least next i want to ask that which is more activating OR or OH

    Reply

  12. This is the kinda answer I was looking for .
    I understood completely what is meant by Ortho para director and deactivating group.

    Reply

  13. Hey James
    Hope you’re well.
    i wanted to ask that if we are given several ortho , para or either meta grps , howw would we know which ortho para will activate the benzene ring most and which meta will deactivate the most ?
    e.g -N(CH3)2 , -NH2 , -OH , OCH3 , -Cl , Br- , I- (ORTHO , PARA)

    e.g -NR3 , CYANIDE ION , -COOH , -CHO , COR- ,

    KINDLY ARRANGE THEM ACCORDING TO THE QS .
    GoD Bless you

    Reply

  15. How does the pathway if we want to turning -CHO as a meta director into ortho and para director? For example if we want to substitute a hydroxyl group to the position of para or ortho on cinnamaldehyde. thans for ur answer.

    Reply

    1. Substitution reactions to install hydroxy groups are very difficult. In theory you could nitrate, reduce to NH2, convert to diazonium, and then KOH, but in practice, you could start with benzaldehyde and install a temporary directing group for directed ortho lithiation followed by an oxygen electrophile

      Reply
  18. Pingback: Ortho-, Para- and Meta- Directors in Electrophilic Aromatic Substitution – Master Organic Chemistry | LiveNRGY

  21. This article is quite detailed. But how does this ortho para affect the difference in boiling points and melting points when it comes to isomerism.

    Reply

  22. Hi James, thank you for the brilliant article?
    What if we have a trityl as a substituent? I believe it should be a meta director since the carbon would be quite electrophilic due to the -I effect of the phenyl group. Thoughts?

    Reply

    1. Why would you choose to have trityl as a substituent? You have three phenyl groups which could interfere with your desired EAS. I think you should comment with a pic of what you’re proposing.

      Reply

  26. “In the second pattern, the meta– product dominates, and the ortho- and meta– products are minor.”
    Just FYI, I think you meant to say “ortho- and para- products are minor”
    :)

    Reply

  27. Which one would be more acidic
    No2-ch2-cooh. Or
    Me3N(+)-ch2-cooh

    Shouldn’t it be the 2nd one as it is Me3n+ is more e- withdrawing than no2?

    Reply

  28. I know it’s very specific, but definitely interesting how aniline (and maybe even phenol), direct meta when they are nitrated or sulfonated, mainly because the lone pair on the nitrogen of the aniline gets protonated by the H2SO4, making it a meta director. It’s a very small point but it would have saved me a few points on a test!

    Reply

  29. Great article! But, what if you have a Ph group as an substituent? Is it considered as a alkyl group as far a being a o,p, director?

    Reply

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