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How to easily find which is +m and-m group and what is way to find it

How to easily find which is +m and-m group and what is way
to find it

Grade:11

5 Answers

Arun
25750 Points
4 years ago
+M effect- groups which have lone pairs (also incld functional groups with lone pairs) , all methyl grps (due to hyperconjugation), groups with a negative charge
-M groups- groups with positive charge, functional groups with no lone pair(eg NO2)
Remember - halogens show +m effect and -I effect but their -i effect is more dominating while in other functional groups +M is more dominating if they show +M and -I ( -OCH3)
 
Vikas TU
14149 Points
4 years ago
Dear student 
-M Effect is shown by groups which decreases the electron density on benzene.
+M Effect is shown by groups which increases the electron density on benzene ring.
Good Luck 
ANKIT DHAKAD
32 Points
4 years ago
+M Group has lone pair or - ve charge and - M group has +ve charge or conjugate system which has more EN than other conjugate system example is ph-cho, Cho is a - M group bcz it has more EN than C=C bond in benzene 
Srinivasan S
27 Points
3 years ago
All answers mentioned earlier are correct. I suggest an easier solution. If you know your periodic table well enough.
 
Consider Ar – X-Y (where Ar is aryl ring, X is an atom (not group) attached directly to Ar and Y is an atom attached directly to X). Here, when:
 
  1. X belongs to a higher group in the periodic table than Y (e.g. -OH, -CH3, -NH2 etc.), then XY is o-/p- directing.
  2. X belongs to a lower group in the periodic table than Y (e.g. NO2, COCH3, CN etc) then XY is m-directin
Hope this helps
Srinivasan S
27 Points
3 years ago
I missed out that in all o-/p- directing it is +M effect (e- donating) and all m-directing, it is -M (e-  withdrawing effect)

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