In previous work [C. A. Chatzidimitriou-Dreismann et al., J. Chem. Phys. 113, 2784 (2000)] we provided first results of the subfemtosecond dynamics of C-H bond dissociation of solid fully protonated polystyrene at Tapproximate to295K, applying neutron Compton scattering (NCS). A striking anomalous shortfall of the proton scattering intensity with respect to that of the carbon nucleus has been observed. A theoretical explanation based on short-lived protonic quantum entanglement (QE) has also been given. Here we present a twofold extension of that work: Investigation of the found anomaly (i) in solid D-polystyrene with various degrees of aromatic protonation [(-CD2CDC6HxDy-)(n) with x + y = 5] and (ii) in liquid C6H6 and C6H6-C6D6 mixtures. A striking decrease of the neutron cross-section density of H by 20% (on the average) was observed, which appeared to be weakly dependent on the H:D atomic ratio. This result indicates that the considered effect is mainly of intramolecular origin. In contrast to previous NCS experiments on metallic hydrides which revealed a strong scattering time (tau(scatt)) dependence of the decrease of the neutron cross-section density of H, this effect is only slightly apparent in polystyrene and benzene, thus indicating different dynamics of the decoherence process due to different electronic environments. All presented results imply that short-lived QE may be highly relevant for chemical and biological systems.