What will be the increasing order of basic strength of the following compounds?

\(C_2H_5NH_2,\, \ (C_2H_5)_2NH,\, \ (C_2H_5)_3N,\, \ C_6H_5NH_2\)

\(C_6H_5NH_2 < C_2H_5NH_2 < (C_2H_5)_3N < (C_2H_5)_2NH\)

The correct answer is option 2. \(C_6H_5NH_2 < C_2H_5NH_2 < (C_2H_5)_3N < (C_2H_5)_2NH\).

To determine the increasing order of basic strength of the given compounds (\(C_2H_5NH_2\), \((C_2H_5)_2NH\), \((C_2H_5)_3N\), \(C_6H_5NH_2\)), we need to consider how readily each compound's nitrogen atom can donate its lone pair of electrons to accept a proton. This is influenced by the inductive and resonance effects of the substituents attached to the nitrogen.

\(C_6H_5NH_2\) (Aniline):

Resonance Effect: The phenyl group (benzene ring) has a resonance effect that delocalizes the lone pair of electrons on the nitrogen into the aromatic ring. This resonance effect decreases the electron density on the nitrogen, making it less available to accept a proton.

Basicity: Due to the resonance effect, aniline is the least basic among the given compounds.

\(C_2H_5NH_2\) (Ethylamine):

Inductive Effect: The ethyl group is an electron-donating group via the inductive effect, which increases the electron density on the nitrogen, making it more basic than aniline.

Basicity: Ethylamine is more basic than aniline because the lone pair on nitrogen is more available for protonation.

\((C_2H_5)_3N\) (Triethylamine):

Inductive Effect: Three ethyl groups provide a strong inductive effect, increasing the electron density on the nitrogen. However, the steric hindrance caused by the three bulky ethyl groups around the nitrogen can make it harder for the nitrogen to access protons.

Basicity: Despite the increased electron density, the steric hindrance slightly reduces the availability of the lone pair for protonation compared to diethylamine, making it less basic than diethylamine.

\((C_2H_5)_2NH\) (Diethylamine):

Inductive Effect: Two ethyl groups provide a significant inductive effect, increasing the electron density on the nitrogen without causing excessive steric hindrance.

Basicity: Diethylamine is more basic than both ethylamine and triethylamine because it has a high electron density on nitrogen with less steric hindrance compared to triethylamine.

Based on the inductive and resonance effects, the increasing order of basic strength is:
\(\text{C}_6\text{H}_5\text{NH}_2 < \text{C}_2\text{H}_5\text{NH}_2 < (\text{C}_2\text{H}_5)_3\text{N} < (\text{C}_2\text{H}_5)_2\text{NH}
\)

Therefore, the correct option is 2. \(C_6H_5NH_2 < C_2H_5NH_2 < (C_2H_5)_3N < (C_2H_5)_2NH\)