On the Strength of the CH…O Hydrogen Bond and the Eclipsed Arrangement of the Methyl Group in a Tricyclic Orthoamide Trihydrate

A maximum of 3.0 kcalmol−1 should be the total energy of the three CHO hydrogen bonds in the trihydrate of 1 according to the results of the calculations described here. This is substantially less than the energy needed to overcome the rotational barrier of the methyl group, which would thus rationalize the highly unusual eclipsed conformation about the CCH3 bond found in 1·3 H2O experimentally. Further investigations are needed for the complete understanding of this phenomenon.