Transmission of substituent effects through 5-membered heteroaromaticrings isinvestigated theoretically at the RHF/6-31+G* and B3LYP/6-31+G* levelsusing the deprotonation equilibria of phenol analogues with heteroatoms Y = NH, O, PHand S. The incr ease in the resonance delocalization of the $pilone-pair$ on the phe-nolic oxygen atom, $npi(O)$, accompanied with the deprotonation depends on the heteroatom Y,in the order NH < O < PH < S. This represents the $pielectron$ accepting ability, or conversely reverse order of the $pielectron$ donating ability of the $pilone-pair$ on Y, $npi(Y).$ The transmission efficiency of substituenteffects is, however,in the reverse order NH > O > S, which represents the order of delocalizability of $npi(Y).$ A better correlation is obtained with ${sigma}p$ - than with ${sigma}p$ for the Hammett type plots with the positive slope, $ ho-$ > 0, of the magnitude in the same order as that for the delocalizability of $npi(Y).$ Thedeprotonation energy, ΔG = [G(PA) + G(H+)] -G(P), decreases with the increasein the extence delocalization in the order NH > O > PH > S.