The hydrogen bond basicity scale pK(HB) (logarithm of the formation constant of 4-fluorophenol-base complexes in CCl4) has been measured for nitro-compounds. This thermodynamic basicity scale is correlated to a spectroscopic basicity scale. The Yukawa-Tsuno equation is obeyed in the nitroaromatics. We have shown that nitroenamines are the most basic nitro-compounds presently known and have hydrogen bond basicity comparable to tributylamine.