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KEAM 2012 Physics and Chemistry Paper

Question : 76 of 120

Marks: +1, -0

Which one of the following is the correct order of increasing basic strength of nitrogen compounds in aqueous solution?

$\mathrm{(A).NH_3}\;<$	$\mathrm{C_2H_5NH_2}\;<$	$\mathrm{C_6H_5NH_2}\;<$	$\mathrm{(C_2H_5)_2NH}\;<$	$\mathrm{C_6H_5CH_2NH_2}$
$\mathrm{(B).C_6H_5NH_2}\;<$	$\mathrm{NH_3}\;<$	$\mathrm{C_6H_5CH_2NH_2}\;<$	$\mathrm{C_2H_5NH_2}\;<$	$\mathrm{(C_2H_5)_2NH}$
$\mathrm{(C).(C_2H_5)_2NH}\;<$	$\mathrm{C_6H_5CH_2NH_2}\;<$	$\mathrm{NH_3}\;<$	$\mathrm{C_2H_5NH_2}\;<$	$\mathrm{C_6H_5NH_2}$
$\mathrm{(D).C_6H_5CH_2NH_2}\;<$	$\mathrm{C_2H_5NH_2}\;<$	$\mathrm{NH_3}\;<$	$\mathrm{C_6H_5NH_2}\;<$	$\mathrm{(C_2H_5)_2NH}$
$\mathrm{(E).C_2H_5NH_2}\;<$	$\mathrm{C_6H_5NH_2}\;<$	$\mathrm{NH_3}\;<$	$\mathrm{(C_2H_5)_2NH}$	$\mathrm{C_6H_5C_2NH_2}$

Validate

Solution:

Basic character depends upon the availability of lone pair of

\mathrm{N}

atom for donation. Presence of electron donating group like

\text{-R},

increases the electron density at

\mathrm{N}

-atom and thus makes its lone pair more available for donation.

Aromatic amines are generally less basic because of the involvement of lone pair of nitrogen in delocalisation. Thus, the correct order of increasing basic strength is

\mathrm{C}_6\mathrm{H}_5\mathrm{NH}_2\; < \;\mathrm{NH}_3\; < \;\mathrm{C}_6\mathrm{H}_5\mathrm{CH}_2\mathrm{NH}_2\; < \;\mathrm{C}_2\mathrm{H}_5\mathrm{NH}_2\; < \;(\mathrm{C}_2\mathrm{H}_5)_2\mathrm{NH}

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