Substituted ring are separated into two groups based on the form of the substituent that the ring carries:Activated rings: the substituents ~ above the ring are groups that donate electrons. Deactivated rings: the substituents top top the ring are groups that retract electrons.
You are watching: Why are halogens ortho para directors but deactivating
Examples of activating groups in the loved one order from the many activating group to the least activating:
-NH2, -NR2 > -OH, -OR> -NHCOR> -CH3 and also other alkyl groups
with R together alkyl teams (CnH2n+1)
Examples that deactivating teams in the loved one order from the most deactivating to the the very least deactivating:
-NO2, -CF3> -COR, -CN, -CO2R, -SO3H > Halogens
with R together alkyl groups (CnH2n+1)
The order of reactivity among Halogens indigenous the an ext reactive (least deactivating substituent) come the the very least reactive (most deactivating substituent) halogen is:
F> Cl > Br > I
The bespeak of reactivity the the benzene rings towards the electrophilic substitution when it is substituted v a halogen groups, complies with the order of electronegativity. The ring the is substituted v the most electronegative halogen is the most reactive ring ( much less deactivating substituent ) and the ring that is substituted with the least electronegatvie halogen is the least reactive ring ( more deactivating substituent ), once we to compare rings with halogen substituents. Additionally the dimension of the halogen impacts the reactivity that the benzene ring that the halogen is enclosed to. Together the dimension of the halogen increase, the reactivity that the ring decreases.
The direction that the reaction
The activating team directs the reaction come the ortho or para position, which way the electrophile instead of the hydrogen the is ~ above carbon 2 or carbon 4. The deactivating group directs the reaction come the meta position, which way the electrophile substitute the hydrogen the is on carbon 3 through the exemption of the halogens that is a deactivating group however directs the ortho or para substitution.
Activating teams (ortho or para directors)
When the substituents favor -OH have an unshared pair that electrons, the resonance effect is more powerful than the inductive impact which make these substituents stronger activators, since this resonance effect straight the electron towards the ring. In situations where the subtituents is esters or amides, castle are less activating since they type resonance framework that pull the electron thickness away indigenous the ring.
Substituents identify the reactivity that rings
The reaction that a substituted ring with an activating team is quicker than benzene. Top top the various other hand, a substituted ring v a deactivated team is slower 보다 benzene.
Activating teams speed increase the reaction since of the resonance effect. The visibility of the unpaired electron that can be donated to the ring, stabilize the carbocation in the shift state. Thus; stabilizing the intermediate step, speeds up the reaction; and also this is due to the decrease of the activating energy. On the various other hand, the deactivating groups, retract the electrons far from the carbocation developed in the intermediate step, thus; the activation power is raised which slows under the reaction.
ReferencesSchore, N.E. And also P.C. Vollhardt. 2007. Organic snucongo.orgistry, structure and function, 5th ed. Brand-new York,NY: W.H. Freeman and Company. Fryhle, C.B. And also G. Solomons. 2008. Organic snucongo.orgistry, 9th ed.Danvers,MA: Wiley.
Problemsguess the direction that the electrophile substition on these rings:
2. Which nitration product is walking to type faster?
nitration of aniline or nitration of nitrobenzene?
3. Predict the product the the adhering to two sulfonation reactions:
2. The nitration the aniline is going come be quicker than the nitration the nitrobenzene, due to the fact that the aniline is a ring with NH2 substituent and also nitrobenzene is a ring through NO2 substiuent. As described above NH2is one activating team which speeds up the reaction and NO2 is deactivating group that slows under the reaction.