Linear hydrogen bonds

What is the range of OHO bond angles for the linear hydrogen bonds in your sample (see also Chapter 2, Problem 2)7... 

The main difference between hydrogen bond and the halogen bond lies in the propensity of the hydrogen bond to be non-linear [28,29], when symmetry of the complex is appropriate (molecular point group Cs or Ci). In so far as complexes B- ClF are concerned, the nuclei Z Cl - F, where Z is the acceptor atom/centre in B, appear to be nearly collinear in all cases, while the nuclei Z- H - Cl in complexes B- HC1 of appropriate symmetry often show significant deviations from collinearity. This propensity for the hydrogen-bonded species B- HC1 to exhibit non-linear hydrogen bonds can be understood as follows. 

A linear hydrogen-bonded structure VIII has also been proposed, but accounts less satisfactorily for the color. The surprising thing about these complexes is the lack of any measurable exchange of the hydroxyl hydrogen atoms from the hydroquinone moiety to the quinone moiety... 

Remarkably enough, dialkoxyterephthalic acids, both in 2D and 3D, form linear hydrogen bonded strands which are reminiscent of the rigid rods formed from alkyl substituted poly-para-phenylenes. 

Fig. 2 Linear hydrogen bonded chain structure formed between [18]crown-6 and [Cu(NH3)4 (H20)P [21]...

Note added in proof, (viii) Suppose liquid water is excited by a short intense pulse of frequency selected infra-red radiation. Let the frequency be chosen to coincide with OH stretching in one of the inferred subcomponents (linear hydrogen bonds, bent hydrogen bonds, etc.). Finally, suppose the incident pulse is intense... 

The simple conception of a tight turn as approximately planar with a linear hydrogen bond is fairly accurate for type II. However, even an ideal type I turn is decidedly nonplanar, with the NH and CO of its... 

The right-handed a-helix (ur) is one of the most common secondary structures. In this conformation, the peptide chain is wound like a screw. Each turn of the screw (the screw axis in shown in orange) covers approximately 3.6 amino acid residues. The pitch of the screw (i. e., the smallest distance between two equivalent points) is 0.54 nm. a-Helices are stabilized by almost linear hydrogen bonds between the NH and CO groups of residues, which are four positions apart from each another in the sequence (indicated by red dots see p. 6). In longer helices, most amino acid residues thus enter into two H bonds. Apolar or amphipathic a-helices with five to seven turns often serve to anchor proteins in biological membranes transmembrane helices see p. 214). 

Non-linear hydrogen bonds pass diagonally across the empty cation sites in the goethite stmcture. These bonds help link the chains of octahedra the hydrogen bond joins an On of one octahedron to an Oj of an octahedron in a chain diagonally... 

Fig. 7.2. The effective valence, s, as a function of 0-0 distance (7 oo)- AB is Rmir. and A B is iJunstrained from Fig. 6.4 ED shows the distance expected for a linear hydrogen bond uncorrected for 0-0 repulsion (based on the thin line of Fig. 7.1) CD shows the distance expected for a linear hydrogen bond corrected for 0-0 repulsion (based on the heavy line of Fig. 7.1) CF is the minimum value of iJoo observed for maximally bent hydrogen bonds (based on the broken line in Fig. 7.4).

Figure 7.3 displays these same results in a different way by plotting A, rather than s, against the 0-0 distance. Although Ah is the same as s for linear hydrogen bonds, it is not the same if the bonds are bent. Since the O O distance... 

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