Explain orientation effect mono substituted benzene
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Orientation and directive influence in mono and di substituted substituted benzene:
It talks about the nature of product when substituted benzene undergoes electrophilic substitution reaction. When un substituted benzene undergoes electophilic substitution reaction reaction, all six carbon atoms are equal. So the incoming electrophile can go at any one of the carbon atom. Whereas if mono and di substituted benzene undergoes electrophilic substitution depending upon the group which present in the benzene ring, the incoming electrophile can go either ortho/para or meta position to the the substituent.
If electron pumped to the the aromatic pi ring by some means, namely +I, +M effect, the aromatic ring will be activated. In such cases the the relative electron density will be higher at ortho/para than meta position with respect to the substituent. So this type of groups are called activating ortho/para directing groups. Eg. CH3-, C2H5-, OH, -OCH3, -OC2H5, -NH2, -NHR, -NHCOCH3 etc.( Note: here the rate of substituted benzene is higher than unsubstituted benzene)
If the otherway electron withdrawn from the ring by -I or -M effect then the system is said to be deactivated. That is relative electron density at met will be higher than ortho/para. So the incoming electrophile will go and attached at meta position to the existing substituent. So this type of groups are called deactivating meta directing group. Eg. -NO2, -CHO, -COOR, -CN, etc. (Note:here the rate of substituted benzene is lower than unsubstituted benzene)
The third one is deactivating ortho/para directing group/subsituent: Halogens (Cl, Br and I) are coming under this category. Here both -I and +M effects are operating. Due to -I effect of halogen substituent the relative rate (rate of the reaction) of halogen substituted benzene is slower than the reaction of benzene towards electrophilic substitution reaction. So it is said to be deactivating. While the lone pairs present on halogen will be given to pi ring, the incoming electrophile directed to orth/para position with respect to halogen. So it is said be ortho/para director. Hence deactivating ortho/para directing.
Similarly, if more than one substituent present then, the one which is dominating over other group, will decide the incoming electrophile attachment on the benzene ring.
Hope this will clarify your doubt.
For more info about Elecrophilic aromatic substitution reaction go through Advanced organic Chemistry by Morrison and Boyd.
Thank you
It talks about the nature of product when substituted benzene undergoes electrophilic substitution reaction. When un substituted benzene undergoes electophilic substitution reaction reaction, all six carbon atoms are equal. So the incoming electrophile can go at any one of the carbon atom. Whereas if mono and di substituted benzene undergoes electrophilic substitution depending upon the group which present in the benzene ring, the incoming electrophile can go either ortho/para or meta position to the the substituent.
If electron pumped to the the aromatic pi ring by some means, namely +I, +M effect, the aromatic ring will be activated. In such cases the the relative electron density will be higher at ortho/para than meta position with respect to the substituent. So this type of groups are called activating ortho/para directing groups. Eg. CH3-, C2H5-, OH, -OCH3, -OC2H5, -NH2, -NHR, -NHCOCH3 etc.( Note: here the rate of substituted benzene is higher than unsubstituted benzene)
If the otherway electron withdrawn from the ring by -I or -M effect then the system is said to be deactivated. That is relative electron density at met will be higher than ortho/para. So the incoming electrophile will go and attached at meta position to the existing substituent. So this type of groups are called deactivating meta directing group. Eg. -NO2, -CHO, -COOR, -CN, etc. (Note:here the rate of substituted benzene is lower than unsubstituted benzene)
The third one is deactivating ortho/para directing group/subsituent: Halogens (Cl, Br and I) are coming under this category. Here both -I and +M effects are operating. Due to -I effect of halogen substituent the relative rate (rate of the reaction) of halogen substituted benzene is slower than the reaction of benzene towards electrophilic substitution reaction. So it is said to be deactivating. While the lone pairs present on halogen will be given to pi ring, the incoming electrophile directed to orth/para position with respect to halogen. So it is said be ortho/para director. Hence deactivating ortho/para directing.
Similarly, if more than one substituent present then, the one which is dominating over other group, will decide the incoming electrophile attachment on the benzene ring.
Hope this will clarify your doubt.
For more info about Elecrophilic aromatic substitution reaction go through Advanced organic Chemistry by Morrison and Boyd.
Thank you
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