Triple bonds defined

In the discussion of metallic radii we may make a choice between two immediate alternative procedures. The first, which I shall adopt, is to consider the dependence of the radius on the type of the bond, defined as the number (which may be fractional) of shared electron pairs involved (corresponding to the single, double, and triple bonds in ordinary covalent molecules and crystals), and then to consider separately the effect of resonance in stabilizing the crystal and decreasing the interatomic distance. This procedure is similar to that which we have used in the discussion of interatomic distances in resonating molecules.7 The alternative procedure would be to assign to each bond a number, the bond order, to represent the strength of the bond with inclusion of the resonance effect as well as of the bond type.8... 

Step 1. ICs are defined as any carbons containing no double or triple bonds to heteroatoms. ICs isolate functional groups from each other according to the classical Hammett concept, so that the treatment of complex structures is simple. 

We need to define what is meant by a double bond equivalent any element-element double bond (C = C, C = 0, C=N) count as 1, while triple bonds count as 2. A saturated ring counts as 1, and any double bond present in the ring also counts as 1 thus a benzene ring corresponds to 4 double bond equivalents. 

The order of a bond may be defined as the number of electron pairs that constitute the bond. Thus the bond orders of single, double, and triple bonds are respectively 1, 2, and 3. As the number of electron pairs forming the bond increases, the attraction of the bonding electrons for the two atomic cores increases, so the bond strength increases and the bond length decreases. 

The differences in selection rules between Raman and infrared spectroscopy define the ideal situations for each. Raman spectroscopy performs well on compounds with double or triple bonds, different isomers, sulfur-containing and symmetric species. The Raman spectrum of water is extremely weak so direct measurements of aqueous systems are easy to do. Polar solvents also typically have weak Raman spectra, enabling direct measurement of samples in these solvents. Some rough rules to predict the relative strength of Raman intensity from certain vibrations are [7] ... 

In summary, the tantalum hydride system adds to the few previously reported well-defined organometallic complexes capable of cleaving N-H bonds of ammonia to yield either an amido or an imido complex, and achieves unprecedented dinitrogen N=N triple bond cleavage with dihydrogen on isolated tantalum atoms to yield reduction of both N atoms. 

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. 

The hollow interior of dodecahedrane and other organic cage compounds described in section 4.9 is much too small to envelop atoms, ions, or molecules. Tight closed-shell macromolecules have been obtained from vesicles by several research groups, by polymerization of amphiphiles possessing double or triple bonds within the membrane or at the head groups. Smaller, but well-defined, closed-shell containers have been obtained by two other methods described below, namely by directed synthesis and by formation of closed-shell all-carbon molecules in graphite vapor. 

The Cu(I)-catalyzed decomposition of (alkynyloxysilyl)diazoacetates 119 furnishes the silaheterocycles 120 and/or 121 (equation 30) in modest yield63. In these cases, the photochemical extrusion of nitrogen from 119 does not lead to defined products and the thermal reaction is dominated by the 1,3-dipolar cycloaddition ability of these diazo compounds. In mechanistic terms, carbene 122 or more likely a derived copper carbene complex, is transformed into cyclopropene 123 by an intramolecular [1 + 2] cycloaddition to the triple bond. The strained cyclopropene rearranges to a vinylcarbene either with an exo-cyclic (124) or an endocyclic (125) carbene center, and typical carbene reactions then lead to the observed products. Analogous carbene-to-carbene rearrangements are involved in carbenoid transformations of other alkynylcarbenes64. 

Hydrozirconation of terminal triple bonds is an essential method to obtain alkenes with defined stereochemistry. In the case of internal alkynes the zirconocene moiety adds to the sterically less hindered position of the triple bond. C/s-selectivity is high, but the regioselectivity is sometimes moderate depending on the nature of the substrate.8... 

The bond order in a diatomic molecule is defined as one-half the difference between the number of electrons in bonding orbitals and the number of antibonding orbitals. The factor one-half preserves the concept of the electron pair and makes the bond order correspond to the multiplicity in the valence-bond formulation one for a single bond, two for a double bond, and three for a triple bond. Fractional bond orders are allowed, but are not within the scope of this discussion. 

An extension of this approach led to the study of some simple molecules in which trivalent phosphorus is bonded to carbon by a double or a triple bond. These spectroscopic experiments have not only yielded conclusive identification but a wealth of molecular information such as geometric and electronic structural data. More importantly, the >C=P- and -CSp moieties could be considered as viable functional groups with interesting and well defined chemical properties. 

Silylenes can be defined as molecules containing a neutral dicoordinate metallene atom possessing two unshared valence-shell electrons. The addition of these short-lived species to double and triple bonds is a practical route for the synthesis of three-membered metallocycles. However, if the [2+1] cycloaddition is followed by insertion of a second silylene molecule, the formation of a four-membered metallocycle takes place. 

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