Which one is more basic aniline or 4-bromoaniline ?

Which one is more basic between aniline and 4-bromo aniline?

Which one is more basic between aniline and 4-bromo aniline that depends on the tendency to donate electron. 4-bromo aniline contains an electron withdrawing group, –Br. 

As a result, the lone pair of electron on nitrogen atom participate in resonance with the pi electron of benzene nucleus  and this electronic charge delocalized  upto the d-orbital of bromine atom present in para-position.

Consequently ,electron pair on nitrogen atom is less available for sharing with other atom , ions or molecule.  

But in case of aniline no such electron withdrawing group is present in any position of benzene ring . 

So in this case electron pair on nitrogen atom is more available for sharing than 4-bromo aniline . 

In addition to ,experimentally  pKa  value of aniline and 4-bromo aniline proved that aniline is more basic than 4-bromo aniline.

Therefore , from the above explanation it is clear that aniline is more basic than 4-bromo aniline.

Which is more acidic between phenol and p-nitro phenol ?

P-nitro phenol is more acidic than phenol . Because ,–NO₂  group  is strong electron withdrawing group. Nitro group ( - NO₂  ) can attract electron from any position of benzene ring ( ortho, meta , para ) due to –I  effect  and -R  effect . 

Therefore,the density of electron of –OH group decrease due to  –I  effect  of –NO₂  group.  Besides this, for –R effect of –NO₂  group, a conjugation occurs between lone pair of oxygen and –NO₂  group.

As a result, –NO₂ group attract O – H bonded electron towards itself. Hence O – H bond becomes more polar and more weak .Consequently, O – H  bond break easily to release proton ( H⁺ ) .

But in case of phenol, O – H  bond is less polar with compare to p-nitro phenol . So the O – H  bond does not break easily .For the above reason p-nitro phenol is more acidic than phenol.

Why is p-chloro phenol more acidic than p-fluoro phenol?

Fluorine is more electro negative than chlorine. That is –I effect of fluorine is greater than chlorine. Therefore, p-fluoro phenol should be more acidic than p-chloro phenol.  

But the actual order is reversed. This anomalous behavior arises due to the delocalization of negative charge of oxygen atom in both compound. 

In case of p-chloro phenol , the negative charge on oxygen atom delocalized to the vacant d-orbital of chlorine atom present in the para-position .

But this is not possible for p-fluoro phenol . Because fluorine atom has no vacant d-orbital. 
Thus the conjugate base of p-chloro phenol is more stable than p-fluoro phenol.   Consequently, p-chloro phenol more acidic than p-fluoro phenol.

Summary

• Which one is more basic aniline or 4-nitroaniline ?
• Which is more acidic between phenol and p-nitro phenol ?
• Why is p-chloro phenol more acidic than p-fluoro phenol ?

What is Friedel crafts acylation reaction . Click here .