Home > Organic Chemistry > Introduction to Reactions and Mechanisms

What is a meta-director?

Answer 1

I assume this question was asked on the basis of aromatic chemistry.

When benzene is substituted by a meta-director, #X#, subsequent aromatic substitutions on the ring are directed to the meta position with respect to #X#.

The classic meta-director is the nitro group, which contains a quaternized nitrogen centre, #-N^(+)(=O)O^-#. When the nitro group is substituted on a benzene ring, it deactivates ALL the positions on the ring to some extent. Nitrobenzene is much less reactive towards electrophilic substitution than say benzene. The ortho and para positions (#2# and #5# with respect to #NO_2#) are ESPECIALLY deactivated because of the unfavourable resonance structure, which you will have to draw and establish for yourself.

On the other hand, the meta positions (#3# with respect to the nitro group), when substituted, give rise to mesomers that are more stable, and more capable of electron delocalization.

In other words, we attempt to account for the experimental result. All I have written here accounts for the experimental observation that meta substitution of substituted arenes is more favourable, when the initial substituent is a deactivating group (and a meta director).

By signing up, you agree to our Terms of Service and Privacy Policy

Answer 2

Nolan Allen

A meta-director is a substituent or functional group in organic chemistry that, when attached to a benzene ring, directs incoming electrophiles to the meta position in an electrophilic aromatic substitution reaction. This occurs due to the withdrawal of electron density from the benzene ring by the meta-directing group. Examples of meta-directing groups include nitro (-NO₂) and carbonyl (-COR) groups.

By signing up, you agree to our Terms of Service and Privacy Policy

Answer from HIX Tutor

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.