Triple bonding, group 13 element compounds

Transition metal bisadduct 138 Transition metal complexes 121,157,158 Transport through cell membranes 43,46 Triazolylboranes 8-9 Triple bonding, group 13 element compounds 75,76... 

A. In the periodic table, silicon is in the same group as carbon. Therefore, it has the same valence electron arrangement and is most likely to have carbon s versatility in forming single, double, and triple bonds and forming compounds with a variety of other elements. 

Carbon is an extremely versatile element because it can form many different compounds. Most of the compounds have one or more functional groups, which contain atoms other than Ccirbon and hydrogen and/or double or triple bonds, and define the reactivity of the organic molecule. 

Elemental silicon is relatively stable in most substances at ordinary temperatures. Silicon shows similarity with other elements of its group, especially with germanium in many chemical properties. It forms tetravalent compounds with tetrahedral geometry almost exclusively. However, only in silicon monoxide, SiO, is its valence +2. Also, unlike carbon, silicon does not form unsaturated double or triple bond compounds. Silicon dissolves in germanium... 

Alkynes are hydrocarbons that contain a carbon-carbon triple bond. A triple bond consists of a cr bond and two tt bonds. The general formula for the alkynes is C li2n-2- The triple bond possesses two elements of unsaturation. Alkynes are commonly named as substituted acetylenes. Compounds with triple bonds at the end of a molecule are called terminal alkynes. Terminal —CH groups are called acetylenic hydrogens. If the triple bond has two alkyl groups on both sides, it is called an internal alkyne. 

The thin control of the energetic characteristics and the electronic transition nature may be carried out by chemical structure alteration. For example the appearance of CH2 group between phenyl ring and triple bond (compounds 3 and 5 in Table 4) interrupts the interaction between it-ekctrons of the both elements. This leads to the short wavelength shift in the absorption and photoconductivity spectra. The insertion of the ethynyl group instead of a CH2 group restores the conjugation. The increase in the numbers and sizes of the... 

The constant x depends on the class of compound (e.g., aromatic vs. aliphatic), ry is the number of specific atoms (e.g., C or Cl), y is a constant specific to that atom and how it is bonded, rij is the number of certain bonds or structural types (e.g., double or triple bonds or branching), and z is a constant specific to these bonds or structural elements. Lyman et al. (1982) gives a full account of this approach and recommend it as the preferred method when no partition coefficient data are available. However, this method is dated and does not include functional groups containing oxygen, nitrogen, and sulfur atoms. 

In summary, it is noted that multiple bonding between the heavier Group 14 elements E (Ge, Sn, Pb) differs in nature in comparison with the conventional a and 7T covalent bonds in alkenes and alkynes. In an E=Ebond, both components are of the donor-acceptor type, and a formal E=E bond involves two donor-acceptor components plus a p-p n bond. There is also the complication that the bond order may be lowered when each E atom bears an unpaired electron or a lone pair. The simple bonding models provide a reasonable rationale for the marked difference in molecular geometries, as well as the gradation of bond properties in formally single, double and triple bonds, in compounds of carbon versus those of its heavier congeners. 

The elusiveness of stable compounds with a triple bond between two group 14 elements (see Section VI.A) makes their synthesis, isolation and characterization one of the holy grails of main-group chemistry. In view of the many experimental failures to produce such compounds, even as short-lived intermediates (except for a few successes, see Section VI.A), theory remains the only reliable source of information. Furthermore, the calculations can be used to develop and test ideas of how to stabilize this group of compounds, hopefully directing experimentalists to their synthesis and isolation. 

Skeletal formula The representation of an organic compound s carbon-to-carbon bonds by lines. A single line represents a single bond with double and triple lines for double and triple bonds, respectively. The carbon-to-hydrogen bonds are assumed but not shown apart from the outline, but other functional groups or elements use their conventional representation. 

Molecules of heavier main-group elements show significant differences to compounds of elements from the first-octal row of the periodic system. The coordination number of the lighter elements is rarely larger than 4 while many stable molecules of the heavier elements with coordination number 5 and 6 are known. Another difference concerns the stability of molecules with multiple bonds. Many stable molecules with double or triple bonds between the lighter elements are well known, particularly compounds that have C=C, C=N, C=0,... 

Triple-Bond Compounds between Group 14 Elements 21... 

The first stable compound to feature triple bonding to a heavier group 14 elements was the molybdenum-germanium derivative, ( -C5H5)(CO)2Mo=Ge-C6H3-2,6-Mes2. After this sensational work, itwas experimentally... 

Although the addition of H2O to an alkyne resembles the acid-catalyzed addition of H2O to an alkene in some ways, an important difference exists. In the presence of strong acid or Hg " catalyst, the elements of H2O add to the triple bond, but the initial addition product, an enol, is unstable and rearranges to a product containing a carbonyl group—that is, a C=0. A carbonyl compound having two alkyl groups bonded to the C=0 carbon is called a ketone. 

The unique properties of carbon relate to its position in the periodic table. As a second-period element, carbon atoms are relatively small. Therefore, it can easily form the double and triple bonds that are rare in the compounds of related elements, such as silicon. As a Group IV element, carbon can form four bonds, which is more than the other second-period elements this characteristic gives it wide... 

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