Vibrational frequency hydrogen bonding cooperativity

Although, in general sense, the cooperativity applies to all intermolecular interactions, it is particularly important in H-bond interaction because of the relay effect of hydrogen atoms. The H-bond distance tends to decrease as the cluster size increases. The typical characteristics of cooperative effects show the shorter X- H distance, longer X-H distance, larger chemical shift, and large red-shifts of the O-H vibrational frequency. 

Fig. 4.19. Hydrogen and substituent X interact differently and cause shifts in the 1486 cm doubly degenerate benzene vibrations in (a) and (d), where S is stretch, C is contract and B is bend. The vertically oriented C—X bond in (b) adds cooperative C—X interaction which raises the frequency and, in (e) diminishes the cooperative bending interaction which lowers the frequency relative to benzene. In (c) and (f) the two C—X bonds double these effects.

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