Question

What the diffrent between basicity and nucleophicility ?!?!?!

Answer 1

Well basicity is the propensity of the species to act as the electron pair acceptor in an acid-base reaction.....

Explanation:

And thus....

`NH_3(aq) + H_2O(l) rightleftharpoonsNH_4^(+) + ""^(-)OH`

Ammonia here acts a base...an electron pair donor, in aqueous solution as a source of hydroxide ions....and certainly this equilibrium reaction is measurable...`K_b=1.74xx10^-5`.

On the other hand, ammonia could also behave as a nucleophile; the nitrogen-based electron pairs could donate to an electrophilic centre, to form, say, a `C-N` bond....

`H_3C-Br + NH_3 stackrel(NEt_3)rarr H_3C-NH_2 + Et_3N*HCl`

(And note that in some circumstances, the product methylamine could react with further equivalents methyl bromide to give up to `(H_3C)_4N^(+)Br^(-)`)

And here the ammonia has clearly acted as a nucleophile, whereas triethylamine has acted as a base....anyway please read your organic text for further detail.