Experimental infrared spectra for CO adlayers on Pt(111) electrodes having known real-space structures as deduced by scanning tunneling microscopy are compared with predictions extracted from conventional dipole-dipole coupling models in order to test the validity of such treatments for compressed electrochemical adlayers, especially with regard to band-intensity transfer effects. The specific structures considered are (2X2)-3CO and (root 19X root 19)R23.4 degrees-13CO hexagonal adlayers; the former is especially close packed (theta(CO)=75) with a pair of threefold hollow and one atop CO per unit cell, while the latter has a lower coverage (theta(CO)=13/19) and involves largely asymmetric binding sites. The comparisons between dipole-coupling theory and experiment include infrared spectra for various (CO)-C-13/(CO)-C-12 mixtures, thereby exploiting the well-known systematic alterations which are induced in the degree of coupling for a given adlayer. Consistent with an earlier assessment (Ref. 6) the conventional dipole-dipole treatment can account semiquantitatively for the marked higher intensity of the atop relative to the threefold hollow C-O stretching band in the observed infrared spectra even though the occupancy on the latter site is twofold greater and the singleton frequencies are substantially (similar to 280 cm(-1)) different. This coupling-induced intensify transfer toward the higher-frequency band component is likely to be a widespread phenomenon for densely packed adlayers. For the (2X2) adlayer, however, the isotope composition-dependent spectral band frequencies and relative intensities deviate markedly from the experiment. While the inclusion of stochastic broadening effects associated with adlayer disorder improves the situation, a satisfactory fit between theory and experiment requires the incorporation of vibrational coupling associated with short-range intermolecular interactions. For the (root 19X root 19) adlayer, on the other hand, dipole-dipole coupling with stochastic broadening accounts well for the observed spectral behavior. The more pronounced limitation of the conventional theory for the (2X2) structure may well be due to the abnormally high adsorbate packing density enhancing the importance of short-range interactions.