A compound is having both NH group and OH group in its structure. When alkylation is carried out on this compound alkylation took place on NH group not on OH group. The reason may be due to nucleophilicity or basicity, but can anyone give further explanation?
Nitrogen is less electronegative than oxygen and hence it's more nucleophilic.
Dr. B.V.s opinion is at the point! Such properties can be understood directly at the basis of atom properties such as electronegativity (EN for N 3.0, O 3.5 and F 4.0). The higher the EN is the more does the atom "keep the electrons in his sphere" in a covalent bond. As a result OH is a weak nucleophile and may even be acidic towards NaOH (in case of aryl-OH) and NH2 is a base and better nucleophile (with alkyl-NH2 much stronger than aryl-NH2).
This kind of "thinking it back to atom properties" is often helpful in understanding such effects.
The reason for the order of EN as given above is the tendency to come closer and closer to the octet electron configuration of the nobel gas Ne. This is the "driving force" for the electron retaining behaviour of N, O and F in covalent bonds. The closer an element is to the Ne octet the higher its EN is.
You can influence the alkylation by the leaving groups. Alkylation reagents with a hard leaving group like Meerwein salt, dimethylsulfate, magic methyl (methyl fluorosulfonate) or methyl triflate results in O-alkylation of amides. In contrast methyliodide with a soft leaving group leads to N-alkylation. Methylbromide or methyltosylate are in between.
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