Hydrogen-bond connectivity

The pattern of hydrogen bonding between a pair of acylurea derivatives revealed by X-ray analysis was consistent with that predicted by spectroscopic studies. Typical examples are illustrated in Figs. 11 and 12 35-37) two NH — O intermolecular hydrogen bonds connect the two molecules. This holds true for the other acylurea derivative 20 (R8 = CH2Ph)38) and 1 1 complexes whose crystal structures were so far determined. 

Scheme I. The infinite sequence of hydrogen bonds connecting diol molecules...

Another photochemically driven proton transfer occurs in the system 46. This molecule on sublimation at low temperatures crystallizes in form 46a having infinite chains of intermolecular hydrogen bonds connecting zwitterionic molecules. Its fluorescence at such temperatures is essentially that of the acridinium ion. However, on prolonged UV irradiation, conversion to 46b occurs and the... 

Hydrogen bonds connecting different molecules are termed intermolecular, and when they connect groups within the same molecule they are called intramolecular. A simple example of an intramolecular hydrogen bond is seen in the enol form of acetylacetone (see Section 10.1). Carboxylic acids... 

Hydrogen bonding connects the complexes via interactions between the eoordinated water molecule (06) and carbonyl oxygen atoms 03 (2.817(5) A) and 04 (2.764(5) A). The disordered water molecule present in the lattice does not form any significant hydrogen bonds (perhaps accounting for its disorder). ... 

The a-D-glucopyranose residues are present in the Cl (d) conformation (Ia2e3e4e5e), and an intrachain hydrogen bond connects 0-2 and 0-3 of adjacent D-glucopyranose residues. A direct, interchain hydrogen-bond connects 0-2 and 0-6, and 0-2 and 0-5 have a water molecule lying between them to which both are hydrogen-bonded. However, this water molecule is randomly replaced by a potassium ion. 

Definitive x-ray diffraction data on structure I was obtained by McMullan and Jeffrey (1965) for ethylene oxide (EO) hydrate, as presented in Table 2.2a. The crystal consists of a primitive cubic lattice, with parameters as given in Table 2.2a. The common pictorial view of structure I is presented in Figure 1.5a. In that figure, the front face of a 12 A cube is shown, with two complete 51262 (emphasizing hydrogen bonds) connecting four 512. 

Parenthetically, DNA is a fibrous sodium salt of double-stranded ribose-poly-phosphate covalently bonded to precise sequences of the four nucleotides adenine (A), thymine (T), glycine (G), and cytosine (C), with intemu-cleotide hydrogen bonds connecting the two strands, and which, in trios, form one bit of the genetic code. 

Fig. 2.6 a, b. Hydrogen-bond connectivity diagram for maltose monohydrate, a Projection of a section of the crystal structure b schematic connectivity diagram... 

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