1.3.5- trihydroxybenzene , hydrogen bonding

Another class of phenol-binding pyridines has been synthesized by Vogtle (Ebmeyer and Vogtle, 1989 Seel and Vogtle, 1992). In the bimacrocycles [69], those phenols were especially well bound which form hydrogen bonds to all three bipyridine units, for example 1,3,5-trihydroxybenzene derivatives. 

The crystal structures of only three substituted 1,2,4-trihydroxybenzenes are known. All three have the same conformation, determined by intramolecular hydrogen bonding such as in (2 5,4a5 )-4,4a-dihydro-5,6,8-lrihydroxy-7-(2 -hydroxypropyl)-l,2,4a-trimethylphen-anthrene-3,9-ione (38). 

An interesting parameter has to be noted about the hydrophilicity of trihydroxybenzenes, and by extention to other polyhydroxylated compound. The fact that the hydroxyl groups of 1,2,3-trihydroxybenzene, and in a lesser extent those of 1,2,4-trihydroxybenzene, are able to form intramolecular hydrogen bonds leave these hydroxyl less available to generate hydrogen bonds with water, making them more hydrophobic than 1,3,5-trihydroxybenzene. 

The complex l,l -bis(ethenyl -pyridyl)ferrocene was also co-crystallized with 1,3-dihydroxybenzene (resorcinol) and 1,3,5-trihydroxybenzene (phloroglucinol)" to form hydrogen-bonded molecular clips (see Figure 12), which lock the conformation of the organometallic fragment in a dipolar arrangement, a prerequisite for NLO molecules. 

Selectivity of encapsulation of trihydroxyben- glucinol and 1,2,4-trihydroxybenzene to give 1 1 zenes by the bipyridine-based covalent capsules cage complexes, but 18 does not. This result is 16-18 shown in Scheme 2.7 has been studied in explained [24] by host-guest hydrogen bonding [24]. The ligands 16 and 17 encapsulate phloro- within the inner cavities of 16 and 17, which have... 

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