[Melon]

Hello everyone, in my homework I have a reaction as stated in the topic above, and it's a case of Nucleophilic Sub.

In the first reaction I understand that the Br atom exits the molecule to form a carbocation, which is then attack by the nucleophile (the acid with -NH2 group).

However, what I don't get is, rather than the H from the NH2 exiting to form a H+, why  can't the lone pair of electrons on N atom in the acid form a dative bond with the Carbocation, so in the end the H doesn't have to leave the NH2?

Thank you!

[chenbeier]

How do aminoacids normally looks like? Acidgroup and aminogroup. Is the lonepair at nitrogen available? Where is the carbocation bonded.