Covalent bonds, multiple

Conjugation The process of covalently bonding (multiple) copies of a hapten to a carrier protein, usually by means of a linker to distance the hapten from the surface of the carrier protein by a chain of about six atoms. 

Any double or triple bond is often referred to as a multiple covalent bond. Multiple bonds higher than these, such as the quadruple covalent bond, are not commonly observed. 

SOME OTHER ASPECTS OF COVALENT BONDING Multiple Bonds and Bond Order... 

Monatomic Ions with Noble-Gas Electron Configurations Ionic Bonds Covalent Bonds Polar and Nonpolar Covalent Bonds Multiple Bonds Atoms That Are Bonded to Two or More Other Atoms Exceptions to the Octet Rule Metallic Bonds... 

As in the case of NH4 the charge is distributed over the whole ion. By considering each multiple bond to behave spatially as a single bond we are again able to use Table 2.8 to correctly deduce that the carbonate ion has a trigonal planar symmetry. Structures for other covalently-bonded ions can readily be deduced. 

As in the case of ions we can assign values to covalent bond lengths and covalent bond radii. Interatomic distances can be measured by, for example. X-ray and electron diffraction methods. By halving the interatomic distances obtained for diatomic elements, covalent bond radii can be obtained. Other covalent bond radii can be determined by measurements of bond lengths in other covalently bonded compounds. By this method, tables of multiple as well as single covalent bond radii can be determined. A number of single covalent bond radii in nm are at the top of the next page. 

When writing a Lewis structure we restrict a molecule s electrons to certain well defined locations either linking two atoms by a covalent bond or as unshared electrons on a sm gle atom Sometimes more than one Lewis structure can be written for a molecule espe cially those that contain multiple bonds An example often cited m introductory chem istry courses is ozone (O3) Ozone occurs naturally m large quantities m the upper atmosphere where it screens the surface of the earth from much of the sun s ultraviolet rays Were it not for this ozone layer most forms of surface life on earth would be dam aged or even destroyed by the rays of the sun The following Lewis structure for ozone satisfies fhe ocfef rule all fhree oxygens have eighf elecfrons m fheir valence shell... 

Macromolecules bearing reactive groups in the repeat units along their chains are capable of multiple interaction with the matrix. As early as 1973, Wilchek prepared Sepharose-based supports chemically modified by chemisorbed polylysine and polyvinylamine [41]. The leakage of dyes covalently bonded to these supports was reduced remarkably as compared to non-modified Sepharose activated by cyanogen bromide. Thus, stable and high capacity affinity adsorbents could be prepared by the introduction of macromolecular spacers between a matrix and a biospecific ligand. 

When the multiplicity of a complex is the same for ionic or ion-dipole bonds and for covalent bonds, the decision as to which extreme bond type is the more closely approached in any actual case must be made with the aid of less straightforward arguments. Sometimes theoretical energy diagrams can be constructed with sufficient accuracy to decide the question. A discussion of crystals based on the Born-Haber thermochemical cycle has been given by Rabinowitsch and Thilo3), and more accurate but less extensive studies have been made by Sherman and Mayer4). 

Carbon likes to form bonds so well with itself that it can form multiple bonds to satisfy its valence of four. When two carbon atoms are linked with a single bond and their other valencies (three each) are satisfied by hydrogens, the compound is ethane. When two carbons are linked by a double bond (two covalent bonds) and their other valencies (two each) are satisfied by hydrogens, the compound is ethylene. When two carbons are linked by a triple bond (three covalent bonds) and their other valencies (one each) are satisfied by hydrogens, the compound is acetylene. 

The DNA double heUx illustrates the contribution of multiple forces to the structure of biomolecules. While each individual DNA strand is held together by covalent bonds, the two strands of the helix are held together exclusively by noncovalent interactions. These noncovalent interactions include hydrogen bonds between nucleotide bases (Watson-Crick base pairing) and van der Waals interactions between the stacked purine and pyrimidine bases. The hehx presents the charged phosphate groups and polar ribose sugars of... 

The complex hierarchy of native protein structure may be disrupted by multiple possible destabilizing mechanisms. As has been described in the foregoing, these processes may disrupt noncovalent forces of interaction or may involve covalent bond breakage or formation. A summary of the processes involved in the irreversible inactivation of proteins is illustrated in Fig. 3 and described briefly in the following section. Detailed discussions of mechanisms of protein desta-... 

Multiple covalent bonds are formed in each macromolecule and, in general, statistical, polydispersed structures are obtained. In the case of controlled vinyl polymerizations, the average length of the macromolecule is determined by monomer to initiator ratios. If one views these polymerizations as extraordinarily long sequences of individual reaction steps, the average number of covalent bonds formed/chain may be visualized as shown in Scheme 2 ... 

A comparison of the covalent connectivity associated with each of these architecture classes (Figure 1.7) reveals that the number of covalent bonds formed per step for linear and branched topology is a multiple (n = degree of polymerization) related to the monomer/initiator ratios. In contrast, ideal dendritic (Class IV) propagation involves the formation of an exponential number of covalent bonds per reaction step (also termed G = generation), as well as amplification of both mass (i.e. number of branch cells/G) and terminal groups, (Z) per generation (G). 

Where Nc = initiator core multiplicity Nb = branch cell multiplicity NcNbM = number of covalent bonds formed/step... 

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