Arrange the following:
(i) In decreasing order of the `pK_(b)` values:
`C_(2)H_(5)NH_(2),C_(6)H_(5)NHCH_(3),(C_(2)H_(5))_(2)NHandC_(6)H_(5)NH_(2)`
(ii) In increasing order of basic strength:
`C_(6)H_(5)NH_(2),C_(6)H_(5)N(CH_(3))_(2),(C_(2)H_(5))_(2),NH andCH_(3)NH_(2)`
(iii) In increasing order of basic strength:
(a) Aniline, p-nitroaniline and p-toluidine
(b) `C_(6)H_(5)NH_(2),C_(6)H_(5)NHCH_(3),C_(6)H_(5)CH_(2)NH_(2)`
(iv) In decreasing order of basic strength in gas phase:
`C_(2)H_(5)NH_(2),(C_(2)H_(5))_(2)NH,(C_(2)H_(5))_(3)NandNH_(3)`
(v) In increasing order of boiling point:
`C_(2)H_(5)OH,(CH_(3))_(2)NH,C_(2)H_(5)NH_(2)`
(vi) In increasing order of solubility in water:
`C_(6)H_(5)NH_(2),(C_(2)H_(5))_(2)NH,C_(2)H_(5)NH_(2^.)`

Explanation

(i) Stronger the base lesser the `pK_(b)` value.
`C_(6)H_(5)NH_(2) gt C_(6)H_(5)NHCH_(3) gt C_(2)H_(5)NH_(2) gt (C_(2)H_(5))_(2)NH`
Refer In-text Q.4.
(ii) `(C_(2)H_(5))_(2)NH gt CH_(3)NH_(2) gt C_(6)H_(5)NHCH_(3) gt C_(6)H_(5)NH_(2)`
Refer Intext Q. 4.
(iii)(a) p-nitroaniline `lt` aniline `lt` p-toluidine
(b) `C_(6)H_(5)NH_(2) lt C_(6)H_(5)NHCH_(3) lt C_(6)H_(5)CH_(2)NH_(2)`
(iv) `(C_(2)H_(5))_(3)N gt (C_(2)H_(5))_(2)NH gt C_(2)H_(5)NH_(2) gt NH_(3)`
In gas phase reactions, the stabilization of the conjugate acids due to hydrogen bonding is absent.
(v) Since the electronegativity of O is more than that of N, alcohols form stronger hydrogen bonds than amines. Therefore, the b.p. of `C_(2)H_(5)OH` (mol. mass = 46) is higher than those of `(CH_(3))_(2)NH` and `C_(2)H_(5)NH_(2)` (each having mol mass = 45). Further, since the extent of hydrogen bonding depends upon the number of H-atoms on N atom, therefore, `1^(@)` amines with two H atoms on the N atom have higher b.p. than `2^(@)` amines (of comparable molecular mass) having only one H atom on N. Thus, the boiling point of `C_(2)H_(5)NH_(2)` is more than that of `(CH_(3))_(2)NH`. Thus, the b.p.s of given compounds increase as:
`(CH_(3))_(2)NH lt C_(2)H_(5)NH_(2) lt C_(2)H_(5)OH`
(vi) Solubility decreases with increase in molecular mass of amines due to increase in size of the hydrophobic hydrocarbon part and with the decrease in the number of H atoms on the N-atom which form hydrogen bonds. Among the given compounds, `C_(6)H_(5)NH_(2)` has higher molecular mass (93) followed by `(C_(2)H_(5))_(2)NH` (73) while `C_(2)H_(5)NH_(2)` has lowest molecular mass of 45. Thus, the solubility increases in the order :
`C_(6)H_(5)NH_(2) lt (C_(2)H_(5))_(2)NH lt C_(2)H_(5)NH_(2)`