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Question
Arrange the following compounds in an increasing order of basic strengths in their aqueous solutions:
NH3,CH3NH2,(CH3)3N, (CH3)2NH
NH3,CH3NH2,(CH3)3N, (CH3)2NH
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Solution
1. The introduction of an alkyl group into ammonia increases the basic strength.
2. The introduction of a second alkyl group further increases the basic strength, but the net effect of introducing the second alkyl group is very much less marked than compared to the first.
3. The introduction of a third alkyl group to yield a tertiary amine, however, actually decreases the basic strength. This is due to the fact that the basic strength of an amine in water is determined not only by electron-availability on the nitrogen atom but also by the extent to which the cation formed by uptake of a proton, can undergo solvation and thereby become stabilized.
Hence the correct order is: NH3<3o<1o<2o
1. The introduction of an alkyl group into ammonia increases the basic strength.
2. The introduction of a second alkyl group further increases the basic strength, but the net effect of introducing the second alkyl group is very much less marked than compared to the first.
3. The introduction of a third alkyl group to yield a tertiary amine, however, actually decreases the basic strength. This is due to the fact that the basic strength of an amine in water is determined not only by electron-availability on the nitrogen atom but also by the extent to which the cation formed by uptake of a proton, can undergo solvation and thereby become stabilized.
Hence the correct order is:
NH3<3o<1o<2o
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