Trimethylamine, hydrogen-bonded with

An especially interesting case is bis-aryltriazene 26 [50, 51] which is not able to form cyclic dimers, in contrast to bis-arylamidines 17 [49, 52]. The crystal structures indicate a steric hindrance between the formyl CH and the aryl o-CH in 17, leading to a substantial angle between the aryl groups and the molecular skeleton, which allows the approach of two monomers and the formation of the cyclic dimers 17. This steric interaction is absent in 26 and repulsion between aryl protons of two different monomers hinder the cyclic dimer formation. However, 26 can form hydrogen bonds with bases B such as trimethylamine, which catalyze the intramolecular proton transfer from one nitrogen to the other in the complex 27. 

A clear effect of hydrogen bonding is afforded by considering the interaction of alcohols with acetonitrile, CH3CN, and trimethylamine, (CH3)3N. The dipole moments of these molecules are 3.44D... 

The trimethylamine/water system (for 10 isotopomers) was investigated by microwave spectroscopy69. The analysis of the rotational constants indicate a structure with an essentially linear single hydrogen bond (r = 1.818 A in 13). 

Figure 9-1 Possible structures for the hydroiiium ion. (a) The species H9O4 has been observed in the solid state and may be an important contributor in aqueous solution, (b) The species (H20)2iH exhibits a dodecahedral caged stracture in mixed water-trimethylamine cluster ions. The hydroniiim ion (not shown) is encased in the hydrogen-bonded cage with 10 non-hydrogen-bonded protons protaiding from its surface. S. Wei, Z. Shi, and A. W. Castleman, Jr., J. Chem. Phys, 1991, 94, 3268. Structure reproduced by courtesy of the American Institute of Physics.

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