Classification of H bonds

2 Classification of H Bonds In general, H bonding systems can be divided into 

Bonds between three atoms of high electronegativity 

Bonds of type (3) are known as bifurcated H bonds and they occur only rarely  

In the conunon type of arrangement A-H-B, A-H is usually regarded as the donor segment and B as the acceptor of the bond. 

Hydrogen bonds can be linear or bent with the A/H/A or A/H/B angle lying somewhere in the range of 130-180°. Often the angle is 175°, but the lower end is usually considered to represent the limiting condition for the formation of the bond. 

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Fig. 1. Classification of H-bonded liquid-crystalline materials exhibiting homogeneous phases Type A-I association of identical molecules Type A-II association of different molecules...

Hydrogen Bonds ivHh Varying Strengths 505 Table 17.1 Classification of H bonds according to Jeffrey. 

Following our general classification of hydrogen bonds, a negatively polarized hydrogen atom in H-Y, where Y is a less electronegative element than H (e.g., B, Al, Re, K, Mg, etc.), could be considered an unusual or nonconventional proton acceptor. Then the interaction... 

On the basis ofthe Cottesman data set and a set of259 compounds compiled from the literature, we explored the performance of several classification methods combined with different descriptor sets. These include simple ADME-type descriptors (log P, number of rotatable bonds, number of H-bond donors, and acceptors),... 

We will show here the classification procedure with a specific dataset [28]. A reaction center, the addition of a C-H bond to a C=C double bond, was chosen that comprised a variety of different reaction types such as Michael additions, Friedel-Crafts alkylation of aromatic compounds by alkenes, or photochemical reactions. We wanted to see whether these different reaction types can be discerned by this... 

The classification of amorphous carbon films according to carbon bond type and hydrogen content can be represented in a triangular diagram, Fig. 6 [e.g., 70]. The comers at the base of the triangle correspond to graphite (100% sp carbon) and diamond (100% sp carbon). The apex represents 100% H, but the upper limit for formation of solid films is defined by the tie line between the compositions of polyethene, -(CH2) -, and polyethyne, -(CH) -. 

The hydrides of the later main-group elements present few problems of classification and are best discussed during the detailed treatment of the individual elements. Many of these hydrides are covalent, molecular species, though association via H bonding sometimes occurs, as already noted (p. 53). Catenation flourishes in Group 14 and the complexities of the boron hydrides merit special attention (p. 151). The hydrides of aluminium, gallium, zinc (and beryllium) tend to be more extensively associated via M-H-M bonds, but their characterization and detailed structural elucidation has proved extremely difficult. 

I 6 H-bonding Parameterization in Quantitative Structure-Activity Relationships i Drug Design Tab. 6.5 Biopharmaceutics classification for 254 Drugs on the basis of HYBOT descriptors. 

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