Why is no2 electron withdrawing

Electrophilic Aromatic Substitution. Study Tip: Learn to recognise the types of substituents and then break it down into the following : 1 Electron donors activate and direct ortho and para.

Substituents with lone pairs e. The resonance effect only allows electron density to be positioned at the ortho- and para- positions. Hence these sites are more nucleophilic, and the system tends to react with electrophiles at these ortho- and para- sites. This is most easily seen by pushing the curly arrows, see below :. Alkyl substituents e. This is the same effect that allows alkyl groups to stabilise simple carbocations. They overall effect is similar to that described above.

This is a similar effect to that for type 1 except that the electrons are from a bonded pair not a lone pair. Substituents with pi bonds to electronegative atoms e. The resonance decreases the electron density at the ortho- and para- positions. So the methyl group is considered as ortho para directing and activating group. Due to highly electronegative Cl atoms, C of CCl3 becomes significantly positively charged.

Therefore, this carbon pulls electrons w. H whenever it is attached in a molecule. Again, hyper-conjugation explains the additional electron withdrawing power of the para-trifluoromethyl group.

Electron withdrawing groups have an atom with a slight positive or full positive charge directly attached to a benzene ring. This is due to the electron withdrawing group pulling away electrons from the carbon, creating an even stronger positive charge. Electronic configuration of fluorine In organic that effect is inductive effect and in NO2 there is resonance stabilising factor. However coming to electronegativity , flourine is the most electronegative elemnet known yet.

So definitely flourine is more electronegative. In nitrobenzene, on drawing the structure, we see that the nitrogen in - NO2 already has a positive charge, because it has given its lone pair to one of the oxygens. Thus, - NO2 is very good at pulling electrons away. When it is in ortho position, it nehaves as an electron withdrawing group by -I effect and an electron donating group due to mesomeric effect.

When it is in meta position, it behaves as an electron withdrawing group by -I effect. Since the distance has increased as compared to ortho, its effect decreases. Type 2- All groups having their key atom multiply bonded to more powerful element are meta -- directing groups. Type 3- Alkyl groups are ortho, para- directing groups.

Since NO 2 is an electron withdrawing group, a glance at the resonance structures shows that the positive charge becomes concentrated at the ortho-para positions. Thus these positions are deactivated towards electrophilic aromatic substitution. Hence, NO 2 is a meta - director , as we all learned in organic chemistry. The carboxy group is electron - withdrawing both by inductive and by mesomeric mechanisms.

That also makes sense considering it is bonded to two electron - withdrawing , strongly electronegative oxygen atoms. The oxygen atom does indeed exert an electron - withdrawing inductive effect, but the lone pairs on the oxygen cause the exact opposite effect — the methoxy group is an electron -donating group by resonance.

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