[Ksharindam]

Which compound has higher nucleophilicity among NH2OH and NH2NH2?
I am confused that which effect is predominant among alpha effect and electron withdrawing effect of oxygen.

[betterbesafehero]

ofcourse NH2NH2

[betterbesafehero]

Reason : Nucleophilicity parallels basicity in a period.

So NH2NH2 is a better base than NH2OH, also a better nucleophile here in this case..!

I hope you find it reasonable enough.

[Ksharindam]

NH2NH2 is a better base than NH2OH, also a better nucleophile here in this case.

But nucleophilicity depends also on alpha effect.(such as NH3 is more basic than Hydrazine but less powerful nucleophile due to alpha effect).Here in hydroxylamine has two lone pairs on neighbouring oxygen atom(hence better alpha effect) but Hydrazine has one lone pair on neighbouring N-atom.

[betterbesafehero]

But here alpha effect is not predominant. Don't stick to what you have studied.

NH2NH2 is the answer..!

[souro10]

Look for the differences in the two bases: Substituent is an -NH₂ group in one case and substituent is an -OH group in the other case.

I think the ease at which the substituent donates electrons is the important factor to look for here.

Nitrogen has 7 protons pulling it's electrons while Oxygen has 8 protons to pull it's electrons.
Consequently, Nitrogen pulls it's electrons less tightly than oxygen , which implying the electron-nucleus distance in case of - NH₂ is greater than that of -OH. Thus electrons of NH₂ are donated more easily than -OH, i.e NH₂-NH₂ is more basic than NH₂-OH, in this case.

Thanks to @Orgopete for this wonderful approach.
Corrections and comments welcomed.

[betterbesafehero]

That's what I am saying. Ease of donating electron decreases along the period..!

[souro10]

That's what I am saying. Ease of donating electron decreases along the period..!

That is not a reason. That is the statement of a particular pattern - but not the reason.

[Babcock_Hall]

Do you have any rate constant data that bear on this question?

[betterbesafehero]

I

That's what I am saying. Ease of donating electron decreases along the period..!

That is not a reason. That is the statement of a particular pattern - but not the reason.

In chemistry we don't give a reason, we see what's happening and accordingly give the theory. Any reason which explains the behavior of reaction or anything, we say that this must be happening, in chemistry there is nothing certain.

Example: VBT explained that CH4 must be tetrahedral, when it was actually determined that CH4 is tetrahedral, we said that: yes..! this must happening and this theory is correct. Reason are just manifestation. Chemistry happens at molecular level, of which many things are yet to be determined, or I can say most of it is yet to be determined.

You are giving an explanation which can be true or not. I am no one to judge it. But I go by facts, that this happens generally, so this must be happening.

[betterbesafehero]

Do you have any rate constant data that bear on this question?

 NH2NH2 Kb=1.7 x10-6
 NH2OH Kb=1.1x10^-8

[souro10]

Do you have any rate constant data that bear on this question?

 NH2NH2 Kb=1.7 x10-6
 NH2OH Kb=1.1x10^-8

The rate constants you mention are basicities. These are thermodynamic properties, and nucleophilicity is a kinetic property.

Bromine is more basic than Iodine but Iodine is more nucleophilic than Bromine [ in a protic solvent ].
Thus equilibrium constant [basicity] cannot and does not reflect nucleophilicity.

[betterbesafehero]

I know that, here nucleophillicity and basicity have same trend, Do I need to scream about it ?This question is solved...would you mind wasting your time on some other questions.

[betterbesafehero]

The rate constants you mention are basicities. These are thermodynamic properties, and nucleophilicity is a kinetic property.

Bromine is more basic than Iodine but Iodine is more nucleophilic than Bromine.

Really..! I didn't know that . That's a group trend, there nucleophillicity is opposite to that of basicity, and in a period both are parallel.

[souro10]

I know that, here nucleophillicity and basicity have same trend, Do I need to scream about it. This question is solved...would you mind wasting your time on some other questions.

This is not the correct approach to learning.
Why does nucleophilicity parallel basicity across a period?