Bond semipolar

In this process an electron pair, shared by a N and an O atom, is moved completely to the O atom. This is equivalent to the transfer of one electron from the N to the O atom, and by this process the N atom acquires a positive charge of one unit, whereas the oxygen atom obtains a negative charge the double covalent bond is transformed into one single covalent bond plus an ionic one. This type of bond is called a semifiolar bond. By assuming a sufficient number of semipolar bonds, all the other oxides with an even number of... 

In the oxides with semipolar bonds we have a second example of the coexistence of covalent and ionic bonds in one molecule. The oxide N20 is a very unusual compound. By electron diffraction measurements it has been discovered that the molecule is linear, and that the two N atoms are directly connected. For this molecule, then, the following electronic structures are possible... 

There are combinations of covalent and ionic bonds other than those observed in PC15 and the semipolar bonds in N2Os. For the ion N02, different electron configurations can be constructed, but since this compound has an odd number of electrons, these configurations cannot have only normal octets. If, however, one electron is taken away, the ion NO can be given different structures with normal octets, e.g. 

Since all these states have the same number of double bonds and semipolar bonds, the energy of the four states will be almost equal, and the different states will occur with almost the same frequency. 

In Section 54 ample evidence was given for the existence of stable multiple bonds in the oxides of group II. In this group, sulphur forms a transition to the following group. In the lower oxide SOs two double or semipolar bonds must be assumed... 

The structure SeOs in the gaseous or solid state is unknown, but in the lower oxide there is polymerization. In Se02 there are two double or semipolar bonds, but in the solid state the compound forms chains... 

Bromine forms the same type of compounds, viz. the very unstable hypobromites AOBr and the bromates ABr03. In all these reactions the double bonds in the oxides become semipolar bonds in the complex ions. 

The term is preferred to the obsolescent synonyms coordinate link , co-ordinate covalence , dative bond semipolar bond . 

The differences have the sign and magnitude which is associated with a mixed bond, and this confirms the structure assigned on p. 52. The ethyl ester of phenylmethylphosphinic acid had a paraehor of 420-5 that calculated on the assumption of an ordinary double bond was 442-1, while on the assumption of a mixed or semipolar bond it was 417-3. The structure was therefore given as... 

Structure.—Many possible structures may be assigned to the molecule. Whichever of these is adopted the phosphorus must be quinque-valent according to the old representation, or quadrivalent with a semipolar bond according to the octet theory. Thus... 

Orient formulae so that the principal heteroatom is at the bottom and the numbering proceeds counterclockwise around the ring. Always write in double bonds, do not use circles in rings. For mesoionic compounds, give (one of) the most important canonical forms. Do not use semipolar bonds, i.e., use —0 , and not N - O for fV-oxides. 

Pyrazolin-5-ones react with salts of various metals to form compounds in which the pyrazolinone has reacted in its enolic form with replacement of the enolic hydrogen to give a salt and having semipolar bonds formed by donation of electrons to the metal by the nitrogen atoms393 394 Usually these compounds contain the number of pyrazolinone residues corresponding to the valence of the metal atom. Such salts as cuprous iodide, ferric iodide, cobaltous iodide, silver iodide and silver diiodide participate in such reactions.393,394 In addition, complexes may be formed in which there has been no elimination of a small molecule between the reactants and no formation of ionic bonds.432... 

Various substituted 2-pyrazolin-5-ones react with metal salts with replacement of hydrogen and formation of semipolar bonds with electron donating atoms. The most important of these compounds are the metal complexes of 4-arylazo-2-pyrazolin-5-ones. These complexes are widely used in the dye industry to give desired properties to 4-arylazo-2-pyrazolin-5-one dyes. Although a large number of metal-dye complexes have been used in dyeing, only a few such compounds have been characterized and reported in the literature. Usually a solution of the azo compound and an appropriate salt such as cupric chloride or nickel sulfate are mixed in solution and heated.326 The reaction is... 

Covalent semipolar bonds result if an s-hole is available in the valence shell of X. This is in line with the donor-acceptor description given above. 

If the positive charge of X is increased to X, or if X is excited to a state with pronounced s-holes, then the corresponding NeX and Ar" species are covalently bound for the same reasons discussed for HeX. The semipolar bond between Ng and X"" is formed by sharing of the two 2pa electrons of Ne or Ar. Alternatively, two 2pn electrons of Ne or Ar could be donated to X. However, the acceptor ability of X with regard to n electrons is much lower. There is no 7i-donation by Ne or Ar towards X" ". 

A dipole moment of 1.46 x 10 Cm (4.38 D) for the nitrogen-oxygen bond is larger than the moments of other semipolar bonds (3). The spatial arrangement around nitrogen in amine oxides is tetrahedral as in quaternary ammonium salts. Tetrahedral configuration was demonstrated by Meisenheimer, who separated iV-ethji-iV-methjianiline iV-oxide [825-19-4] into its optical isomers (4), and later confirmed by electron diffraction studies ( ) ... 

The coordinate link is, of course, electrically unsymmetri-cal and has considerable ionic character hence the names semipolar bond and coionic link, which are also used for this type of binding. Molecules containing the coordinate link usually show a pronounced electrical dipole moment that is, they will tend to turn and orient themselves when they are placed in an electric field just as a compass needle orients itself in a magnetic field. 

For there to be <8 electrons in the valence shell of the sulfur atom in SFe, the polarity of the molecule must be S (F )6 with x>2. (For an explanation, click here http //bit.lv/fM3PNf or see Appendix 5.) Quantum-mechanical calculations give x 3. This corresponds to the semipolar bond structure ... 

As a group the compounds with such phosphorus-to-carbon semipolar bonds are known as ylides or, occasionally, as Wittig reagents (Chapter 10), and they are commonly prepared from the corresponding phosphonium salts, for example, methyl-triphenylphosphonium bromide [(C6H5)3PCH3 Br ]. 

Coordinate Covalent Bond n A covalent bond in which both shared electrons appear to have been contributed by one atom. (2) coordinate link, coordinate covalent bond, dative bond, semipolar bond, or dipolar bond is a description of covalent bonding between two atoms in which both electrons shared in the bond come from the same atom. The distinction from ordinary covalent bonding is artificial, but the terminology is popular in textbooks, especially those describing coordination compounds. Once such a bond has been formed, its strength and description is no different from that of other polar covalent bonds. An example of a dipolar bond in the ammonium ion. 

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