In comparing hydroxylamine, hydrazine, and methylamine for basicity, the order of increasing basicity is hydroxylamine < hydrazine < methylamine.

I tried to reason this trend based on electron donating power of the -$\ce{OH}$, -$\ce{NH2}$, and -$\ce{CH3}$ groups, however that yields the order of basicity: methylamine < hydroxylamine < hydrazine, because more electron-donating power concentrates electron density on the nitrogen atom, making it more basic.

Other factors, such as steric hindrance, do not seem to be impacting anything here, because $\ce{-OH}$, $\ce{-NH2}$, and $\ce{-CH3}$ groups are all around the same size.

What is the key factor that influences the basicity here? I realize that hydrazine has two nitrogen atoms, whereas hydroxylamine and methylamine have one nitrogen atom, so that may be affecting the basicity.

  • $\begingroup$ Try this one out. Sort carbon, nitrogen and oxygen according to their electronegativity. $\endgroup$ – user6376297 Apr 16 '19 at 16:52
  • $\begingroup$ O is more electronegative than N, which is more electronegative than C. So the more electronegative substituent decreases the charge density of the nitrogen atom (thereby stabilizing it) and making it less basic, correct? $\endgroup$ – DrPepper Apr 16 '19 at 17:01
  • $\begingroup$ I would say yes. Physical chemists may have a much more sophisticated and articulate explanation, but for a simple organic chemist like myself this seems reasonable. $\endgroup$ – user6376297 Apr 16 '19 at 17:04
  • $\begingroup$ On the other hand, hydrazine is much more basic than ammonia, although H is less electronegative than N. For that one, if I remember correctly, they told us it was because of the repulsion between the electron pairs on the two adjacent nitrogen atoms, so one of the two wants to catch a proton really bad. $\endgroup$ – user6376297 Apr 16 '19 at 17:08

Browse other questions tagged or ask your own question.