Statement I : Basic strength of ${\left({\mathrm{CH}}_3\right)}_2\mathrm{NH}>{\mathrm{CH}}_3{\mathrm{NH}}_2>{\left({\mathrm{CH}}_3\right)}_3\mathrm{N}$

Statement II : Basic strength of ${\left({\mathrm{C}}_2{\mathrm{H}}_5\right)}_2\mathrm{NH}>{\left({\mathrm{C}}_2{\mathrm{H}}_5\right)}_3\mathrm{N}>{\mathrm{C}}_2{\mathrm{H}}_5{\mathrm{NH}}_2$

Basic strength in amines is decided by the cumulative effect of H–bonding, +I effect and steric hindrance

In general,

 Basic strength of $2^{0}a\min e>3^{0}a\min e>1^{0}a\min e$

Ex :${\left({\mathrm{C}}_2{\mathrm{H}}_5\right)}_2\mathrm{NH}>{\left({\mathrm{C}}_2{\mathrm{H}}_5\right)}_3\mathrm{N}>{\mathrm{C}}_2{\mathrm{H}}_5{\mathrm{NH}}_2$

Based on +I effect only (in gas phase) … $3^0>2^0>1^0$

Based on steric hindrance & H–bonding ….$1^0>2^0>3^0$

In methyl amines there is no steric hindrance to H bonding. Hydrogen bonding dominates + I effect

  $\therefore {\left({\mathrm{CH}}_3\right)}_2\mathrm{NH}>{\mathrm{CH}}_3{\mathrm{NH}}_2>{\left({\mathrm{CH}}_3\right)}_3\mathrm{N}$