Covalent bonding double bonds

Double and triple covalent bonds can be formed between elements by the sharing of two or three electron pairs respectively. Consider the formation of ethene (ethylene), C2H4 ... 

Moving now to nitrogen we see that it has four covalent bonds (two single bonds + one double bond) and so its electron count is 5(8) = 4 A neutral nitrogen has five electrons m its valence shell The electron count for nitrogen m nitric acid is one less than that of a neutral nitrogen atom so its formal charge is +1... 

Covalent radii (Table 4.7) are the distance between two kinds of atoms connected by a covalent bond of a given type (single, double, etc.). 

Fiber-Reactive Dyes. These dyes can enter iato chemical reaction with the fiber and form a covalent bond to become an iategral part of the fiber polymer. They therefore have exceptional wetfastness. Thein main use is on ceUulosic fibers where they are appHed neutral and then chemical reaction is initiated by the addition of alkaH. Reaction with the ceUulose can be by either nucleophilic substitution, using, for example, dyes containing activated halogen substituents, or by addition to the double bond in, for example, vinyl sulfone, —S02CH=CH2, groups. 

The stereochemistry of the most fundamental reaction types such as addition, substitution, and elimination are described by terms which specify the stereochemical relationship between the reactants and products. Addition and elimination reactions are classified as syn or anti, depending on whether the covalent bonds which are made or broken are on the same face or opposite faces of the plane of the double bond. 

Note that these compounds are covalently bonded compounds containing only hydrogen and carbon. The differences in their strucmral formulas are apparent the alkanes have only single bonds in their structural formulas, while the alkenes have one (and only one) double bond in their structural formulas. There are different numbers of hydrogen atoms in the two analogous series. This difference is due to the octet rule that carbon must satisfy. Since one pair of carbon atoms shares a double bond, this fact reduces the number of electrons the carbons need (collectively) by two, so there are two fewer hydrogen atoms in the alkene than in the corresponding alkane. 

A large body of experimental evidence confirms that covalent bonds have characteristic distances depending on bond type. Carbon-carbon single and double bond lengths are around 1.54A and 1.32A, respectively, while partial double bond distances, e.g., in benzene, are about 1.40A. 

Synthesis and application in molecular biology of double-helical nucleic acids with covalent-bonded chains 98UK274. 

The oxygen atom O-1 adds to the carbon-carbon double bond, while the oxygen 0-2 forms a covalent bond to the titanium center. As a result complex 5 is... 

Pi (77 ) bond (Section 1.8) The covalent bond formed by sideways overlap of atomic orbitals. For example, carbon-carbon double bonds contain a 7r bond formed by sideways overlap of two / orbitals. 

I topoisomerase of mammals is a 100 kD monomeric protein whose activity is ATP-independent. This enzyme binds to double-stranded DNA and cleaves one of the DNA strands of the duplex, simultaneously forming an enzyme-DNA covalent bond between a tyrosine residue and the 3 -phosphate of the cleaved DNA. The type II topoisomerases are dimeric enzymes, which are ATP-dependant. Two isoforms of topoisomerase II exist, topoisomerase a and (3, with apparent molecular weights of 170 and 180 kD. Topoisomerase... 

In Table VI3) and Fig. 3 there are given radii for use in compounds of this type. The sum of the singlebond radii for two atoms gives the expected distance between these two atoms in such a compound when they are connected by a covalent bond. The sum of their double-bond or triple-bond radii similarly gives the expected distance when they are connected by a double or a triple bond. 

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