Arrange the following amines in order of decreasing base strength. NH3, NH2Br, CH3NH2, (CH3)2NH
Strongest --> Weakest Base:
(CH3)2NH CH3NH2 NH3 NH2Br
Look up Kb in tables and go from there. I know NH3 is 1.8 x 10^-5 and CH3NH2 is 4.8 x 10^-4, dimethylamine (CH3)2NH is 5.9 x 10^-4 but I don't have the other one in the table I have at home.
Hayley is Right
Sure, let's arrange them in order of decreasing base strength:
1. NH3 (Ammonia)
2. CH3NH2 (Methylamine)
3. (CH3)2NH (Dimethylamine)
4. NH2Br (Bromamine)
Ammonia (NH3) is the strongest base since it has no substituents or electronegative atoms. Methylamine (CH3NH2) is slightly weaker than ammonia due to the presence of a methyl group, which slightly decreases its basicity.
Dimethylamine ((CH3)2NH) is weaker than methylamine as the addition of another methyl group further reduces its basicity.
Finally, Bromamine (NH2Br) is the weakest base among the four, as the electronegative bromine atom decreases its ability to accept a proton, making it the least basic.
To determine the order of decreasing base strength among the given amines, we need to consider their structures and the factors that influence their basicity.
The basicity of an amine primarily depends on the availability of its lone pair of electrons, which can accept a proton (H+). The more readily the lone pair is available, the stronger the base.
Now let's analyze each amine:
1. NH3 (Ammonia):
Ammonia has a lone pair of electrons on the central nitrogen atom. It is the simplest amine among the given compounds. Being a primary amine, it can readily donate its lone pair to accept a proton. It is a weak base compared to other amines due to the absence of additional alkyl groups.
2. NH2Br (Bromamine):
Bromamine is formed by replacing one of the hydrogen atoms in ammonia with a bromine atom. The presence of the electronegative bromine atom decreases the electron density on the nitrogen atom and makes it less capable of donating its lone pair. Therefore, NH2Br is a weaker base than NH3.
3. CH3NH2 (Methylamine):
Methylamine is ammonia in which one of the hydrogen atoms is substituted with a methyl (-CH3) group. The methyl group releases electron density towards the nitrogen, making its lone pair more available for proton acceptance. Therefore, CH3NH2 is a stronger base than NH3 and NH2Br.
4. (CH3)2NH (Dimethylamine):
Dimethylamine is ammonia in which two hydrogen atoms are substituted with methyl groups. The presence of the two methyl groups further increases the electron density on the nitrogen atom compared to methylamine. This increased electron density enhances the availability of the lone pair, making (CH3)2NH the strongest base among the given amines.
So, in terms of decreasing base strength:
(CH3)2NH > CH3NH2 > NH2Br > NH3