A substituent top top a benzene ring can result the placement of extr substituents on the ring throughout Electrophilic aromatic Substitution. How do we know where one additonal substituent will most most likely be placed? The answer to this is with inductive and also resonance effects. Inductive impacts are directly correlated with electronegativity. Substituents deserve to either be meta directing or ortho-para directing.

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Introduction

The three basic positions that a disubstituted benzene ring are ortho, meta and also para.

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Figure 1: The effect of an Electron Donating teams on a Benzene Ring

The very first scenario for including an electrophile to a monosubstituted benzene ring is as soon as the substituent is one electron donating group. Electron donating groups are alkyl groups, phenyl groups or substituents that have a lone pair of electrons on the atom directly bonded to the ring. Electron donating groups are donating by induction (Activating and Deactivating Benzene Rings) and resonance. Instances of electron donating groups: -CH3, -OCH3, -OH, -NH2

Electron donating groups reason the second subtituent to include on to the para or ortho place on the benzene ring. The factor for this have the right to be described by the different carbocation resonance structures of the ortho, meta and also para positions.

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Some electron donating groups have an extra resonance type in which there is a dual bond in between the atom and the carbon on the benzene. This is a very stable resonance form. This is because of directing impacts of substituents in conjugation v the benzene ring.

When the electrophile is included to the ortho position, three different resonance creates are possible. Carbocation develops 1 and 2 are an additional carbocations, but position 3 creates a tertiary carbocation and the hopeful charge is on the carbon directly attached to the electron donating group, which is the many stable. This carbocation is likewise stablized through the electrons from the electron donating group. More stable intermediates (the carbocation) have actually lower shift state energies and also therefore a faster reaction rate, forming much more of this product. This is the factor that the ortho position is among the significant products.

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If the electrophile is added to the monosubstituted benzene ring in the para position one of the 3 resonance forms of the carbocations will be a tertiary carbocation i m sorry is extremely stable because of the +I result if the 3 -CH3. This carbocation intermediary is the exact same as the one created from ortho substitution.

For the meta substituted carbocation resonance structures, there room three feasible resonance froms the are secondary carbocations. These forms are not as stable as the tertiary carbocation kind in the ortho and para substituted carbocations.

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Therefore, the two significant products that the reaction that a monosubstituted benzene ring v an electron donating group and extr electrophile space the ortho and para positions. It"s necessary to note that the para product is slightly much more common than the ortho product due to steric hindrance.

H-NMR spectroscopy have the right to be provided to recognize whether or no a compound has actually a second substituent in ~ the ortho or para position. In ~ the ortho place there are four distinctive signals, but for the para place there are just two signals since the molecule is symmetrical. Electron donating groups on a benzene ring are said to be activating, because they boost the price of the second substitution so that it is higher 보다 that of standard benzene.

Electron donating teams are claimed to be ortho/para directing and they space activators.


The result of one Electron Withdrawing team on a Benzene Ring

The other circumstance is as soon as you have add secondary electrophile to a monosubstituted benzene ring through an electron withdrawing group on it. Electron withdrawing groups have an atom with a slight optimistic or complete positive charge directly attached come a benzene ring. Instances of electron withdrawing groups: -CF3, -COOH, -CN. Electron withdrawing groups only have one significant product, the second substituent add to in the meta position. Again, this deserve to be defined by the resonance creates of the carbocation intermediates.

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When the second electrophile is added on to the benzene ring in the ortho position, the exact same three resonance develops of the carbocation room produced. Again, one form is a tertiary carbocation v the hopeful charge top top the carbon directly attached to the electron withdrawing group. Unequal in the case with one electron donating group, this resonance kind is much much less stable. This is due to the electron withdrawing group pulling far electrons native the carbon, creating an also stronger confident charge. This instance holds true because that the para substituted tertiary carbocation resonace type as well.

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For the meta position, every the carbocations developed are secondary. Although these room not completely stable, lock are much more favored than the resonance develops of the ortho and para positions.

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