Chain structures hydrogen fluoride

Karpfen, A., and Yanovitskii, Q., Structure and vibrational spectra of neutral, protonated and deprotonated hydrogen bonded polymers an ah initio SCF study on chain-like hydrogen fluoride clusters, J. Mol. Struct. (Theochem) 307, 81-97 (1994). 

The crystal structure of many compounds is dominated by the effect of H bonds, and numerous examples will emerge in ensuing chapters. Ice (p. 624) is perhaps the classic example, but the layer lattice structure of B(OH)3 (p. 203) and the striking difference between the a- and 6-forms of oxalic and other dicarboxylic acids is notable (Fig. 3.9). The more subtle distortions that lead to ferroelectric phenomena in KH2PO4 and other crystals have already been noted (p. 57). Hydrogen bonds between fluorine atoms result in the formation of infinite zigzag chains in crystalline hydrogen fluoride... 

Due to its strong hydrogen bonds, in the vapor state hydrogen fluoride is found as short chains and rings. Draw the Lewis structure of an (HF)3 chain and indicate the approximate bond angles. 

When the monosaccharide was not available directly after hydrolysis or solvolysis of the polysaccharide, a monomeric derivative for MS analysis could be obtained by a combination of chemical modifications and cleavages. Thus, in order to obtain an open-chain derivative of pseudaminic acid, OPS of S. boydii type 7 (Fig. 4, structure 12) was carboxyl-reduced, hydrolyzed under mild acid conditions, the products were carbonyl-reduced, solvolyzed with anhydrous hydrogen fluoride, and methylated.9,24... 

Table 13. Computed equilibrium structures of cyclic and open-chain hydrogen fluoride trimers... 

The trimer of hydrogen fluoride, (HF)3, does not have an open-chain structure. All experimental evidence points to a symmetric cyclic cluster... 

Figure 8.7. Plots of AE (n) and AE (n) versus Ijn for zigzag chains and for cyclic hydrogen fluoride clusters as obtained at the MP2/6-311+ +G(2d,p) level [52]. Open symbols A (n) filled symbols AE (n) circles cyclic structures squares chains.

Another prototypical system for the study of hydrogen-bonded interactions is liquid hydrogen fluoride. The crystal structure of solid HF shows that the molecules are arranged in parallel hydrogen-bonded zig-zag chains. Small (HF)n cluster on the other hand form cyclic structures in the gas phase. A recent AIMD simulation has helped in characterizing the nature of the liquid for which only indirect experimental data is available. A typical configuration taken out of the AIMD trajectory is shown in Figure 3. 

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