Basicity

[freakJoe]

Which of these molecules is the most basic?

NH3, NH2CH3, NH2NH2 or NH2OH?

[hypervalent_iodine]

I assume this is homework? If so, what do you think? Which part of the molecule is responsible for it being basic?

[freakJoe]

It is a part of theoretical investigation... computational chemistry... and i would like to compare calculation results with some theories. I am not sure if i am correct, but i was thinking about the nature of the group attached to NH2. Is it possible, that thanks to -CH3 substituent, which push electrones towards N atom, it makes the molecule more basic? It would tend to accept extra proton more then for example NH2OH, where -OH group withdraw the electrons...?

[BabcockHall]

One thing to be aware of in comparing the basicities of ammonia and gradually more methyl-substituted amines is that one has to specify gas-phase versus in solution. The order of basicities is different.

[John Cuthber]

It depends on the solvent (or lack of one).

[freakJoe]

no solvent and water?

[BabcockHall]

no solvent and water?

 

Gas-phase acidities are obviously measured in the complete absence of solvent (my recollection is that mass spectrometry is involved, but I don't recall any details). Many pK_a values are measured in water, but many others are tabulated in DMSO. With respect to primary, secondary, and tertiary amines, the relative order of pK_a values is affected by how well the conjugate acid (which is a cation) is solvated by water, as well as electronic effects that are intrinsic to the cation.

Edited May 27, 2016 by BabcockHall

[Albert hofmann]

in my opinion form left to right of increase. Because basicity is mean to, localize and feed consist of electrons. So Nh2oh the most basic

 

i cant exactly explain im sorry i am not Good about english writting

Edited June 29, 2016 by Albert hofmann