Answer:
As the extent of electron delocalization into the ring increases, the geometry at nitrogen flattens. p-Nitroaniline, for example, is planar. Write a resonance contributor for p-nitroaniline that shows the nitro group increases electron delocalization:
This happen due to electron-withdrawing effect of Nitro group
see the attached in the image
Step-by-step explanation:
- What are delocalized electrons ?
The electrons present in a molecule which are not associated with a singlke atom or bond .
In benzene Ring electrons are declocalized because elctrons can be found equally on any of the six- carbons
- How to show delocalization of electron ?
1. Electron moves towards positive charge atom or away from electron-rich atom
2. The movment of electron is shown by the arrow
3. Any group which stablise the excess charge, will increase the delocalization
Delocalisation of Aniline : look at the attached image
In free - NH3 group , The electron Pair (lone pair) of Nitrogen are easily available for donation and NH3 act as base. It has pyramidal shape
But in aniline ( one H of NH3 is replaced by the benzene ring ):
- lone-pair of Nitrogen are deloclized over the benzene ring.
- Hence NH2- group become planar (flattened) and comes in the plane of benzene.
- The lone pair of electrons increase the electron density at ortho and para position of the benzene ring .
In p-Nitroaniline
- Nitro(NO2)- group is present at the para position with respect to -NH2
- This NO2- group is electron withdrawing in nature.
- Electron - withdrawing : those groups that draws the electron density towards themself . Hence they stablise the negative charge.
- NO2- stablises the increased electron density created by -NH2 of aniline . Hence it increases the electron delocalization