Solid solutions hydrogen bonding

This chapter surveys unimolecular and bimolecular photochemical reactions in mixed molecular crystals and solid mixtures. Various photoreactions occurring in mixed crystals (solid solution), hydrogen-bonded cocrystals, donor-acceptor crystals, crystalline organic salts, and solid mixtures are described. In contrast to one-component crystals [2], the organic photochemistry of such multi-... 

With carboxylic acids, the simple dimeric species are reasonably persistent in solution (and the gas phase), but the more extended structures are generally limited to the solid state. Hydrogen bonding between carbonyl oxygen atoms and amino N-H groups has... 

Since A and B are calculated with 6-coordinated elements (7.19), there is a large difference for compotinds with a coordination number different from 6. In solids containing hydrogen bonds, the experimental PZC is lower than the calculated one because hydroxyl ions in the lattice tend to anchor, hydroxyl ions of the solution within the surface layer [4] ... 

Figure Al.7.14. 3.4 mn x 3.4 mn STM images of 1-docosanol physisorbed onto a graphite surface in solution. This image reveals the hydrogen-bonding alcohol molecules assembled in lamellar fashion at the liquid-solid interface. Each bright circular region is attributed to the location of an individual hydrogen...

Hydrogen bonding to a carbonyl group causes a shift to lower frequency of 40 to 60 cm k Acids, amides, enolized /3-keto carbonyl systems, and o-hydroxyphenol and o-aminophenyl carbonyl compounds show this effect. All carbonyl compounds tend to give slightly lower values for the carbonyl stretching frequency in the solid state compared with the value for dilute solutions. 

In the solid state the CH tautomer (78a) is always readily identified, but the OH and NH tautomers (that, in some cases, coexist in the crystal (73CSC469)) are difficult to differentiate due to the strong hydrogen bonds that shift the u(CO) band to the region of pyrazole vibrations. This source of complications is not present in the fixed forms that can always be identified by their IR spectra, both in solution and in the solid state. 

The concept of mesohydric tautomerism was advanced by Hunter and his associates in a series of papers which appeared between 1940 and 1950 (e.g., references 15 and 16). This concept was based on the fact that in all cases where the mobile hydrogen atom would be bonded to oxygen, sulfur, or nitrogen atoms in both possible tautomers, the individual forms had not been isolated. It was further established that many of these compounds were associated both in the liquid state and in solution, and it was concluded that the individual tautomers did not exist. The actual molecules were thought to be intermolec-ularly hydrogen-bonded, the mobile hydrogen atom being bonded equally to both of the hetero atoms. This concept has been useful and has led to clarification of the tautomerism which occurs in solids and... 

As mentioned in Section II,B, solutions of y9-hydroxypyridines in the nonpolar solvents chloroform and carbon tetrachloride show sharp infrared absorption bands near 3600 cm indicating that they exist in the hydroxy form. Infrared spectral data also led Mason to conclude that -hydroxypyridines probably exist largely as such in the solid state and exhibit O— 0 hydrogen bonding, a conclusion which is contrary to an earlier proposal favoring a zwitterion structure. 

In 1951, pyrid-4-thione was concluded from ultraviolet spectral data to exist predominantly as such in ethanolic solution,but no comparisons were made and this conclusion had to be considered as tentative. Pyrid-2-thione has been shown by X-ray crystallography to exist as hydrogen-bonded dimers (201) in the solid state, the posi-... 

In solution and in the solid state, imidazole and its N2-unsubstituted derivatives form large hydrogen-bonded associates 13 (Scheme 8) [76AHC(S1), p. 266 84CHEC-I(5)345,84JPC5882 96CHEC-II(3)77 97JST(415)187]. 

Unexpectedly strong intermolecular hydrogen bonding has been reported by IR spectroscopic studies for tetrahydro-4,7-phenanthroline-l,10-dione-3,8-dicarboxylic acids, which exist in the oxo-hydroxy form 165 in both solid state and in solution [78JCS(CC)369].Tlie conclusion was based on comparison of B-, C-, and D-type bands for 165 and their dimethyl esters (detection of hydrogen bonding) and on analysis of IR spectra in the 6 /xm region (pyridine- and pyridone-like bands). 

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