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Question
Give plausible explanation for each of the following :
Why are amines less acidic than alcohols of comparable molecular masses?
Solution 1
Amines undergo protonation to give amide ion.
`R- NH_2 -> R - bar(N) H + H^(+)`
Amide ion
Similarly, alcohol loses a proton to give alkoxide ion.
`R - OH -> R - bar(O) + H^(+)`
Alcohol Alkoxide ion
In an amide ion, the negative charge is on the N-atom whereas in alkoxide ion, the negative charge is on the O-atom. Since O is more electronegative than N, O can accommodate the negative charge more easily than N. As a result, the amide ion is less stable than the alkoxide ion. Hence, amines are less acidic than alcohols of comparable molecular masses
Solution 2
Loss of proton from an amine gives an amide ion while loss of a proton from alcohol give an alkoxide ion.
R—NH2—>R—NH– +H+
R—O —H—>R— O– +H+ .
Since O is more electronegative than N, so it wijl attract positive species more strongly in comparison to N. Thus, RO~ is more stable than RNH®. Thus, alcohols are more acidic than amines. Conversely, amines are less acidic than alcohols.
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