Q.Can we use nucleophiles such as NH3, CH3O- for the nucleophilic substitution of alcohols?

Step 1. Hydroxide (-OH-) is a strong base and hence a very POOR leaving group -- it does not depart easily even when attacked by a nucleophile.

Step 2. NH3 and CH3O- are themselves comparable in base strength (or weaker as nucleophiles under the relevant conditions) to hydroxide, so they cannot force -OH- to leave directly from an unactivated alcohol.

Step 3. To run a genuine nucleophilic substitution on an alcohol, the -OH must FIRST be converted into a good leaving group -- protonated to -OH2+ with a strong acid, or converted to a halide (with HX, PX3, SOCl2) or a sulfonate ester (tosylate/mesylate). …

Assess whether -OH- is a good enough leaving group for direct substitution (it is not), then note that activation to a halide/sulfonate is …

• Assuming any nucleophile can displace -OH directly just because it is 'nucleophilic enough' -- leaving-group ability (not nucleophile strength) is the limiting factor here. …