Hydrogen bonding—rotational complexes

FIGURE 3.14 Left The electrons in water tend to be pulled more towards the oxygen atom, resulting in an electric dipole moment. Right Structure of the water dimer in the gas phase, showing a typical hydrogen bond. The complex rotates freely about the dashed line the atoms do not always lie in a single plane. 

This vibrational cooling is sufficient to stabilize complexes that are weakly bound by van der Waals or hydrogen-bonding forces. The pure rotational spectra and structure of species such as... 

Heavy atom tunneling of entire alkyl groups between the different sides of the hydrogen bonded ring plane is much less likely even for methanol, in contrast to the analogous but fighter water case [108]. These motions correspond to hindered rotation of the monomer and are slowed down considerably in the complex due to the librational constraints. 

N. Borho and Y. Xu, Molecular recognition in 1 1 hydrogen bonded complexes of oxirane and trans 2,3 dimethyloxirane with ethanol A rotational spectroscopic and ab initio study. Phys. Chem. Chem. Phys. 9, 4514 4520 (2007). 

---