Bonding double and triple

First we need to locate the part of the molecule where resonance is an issue. Remember that we can push electrons only from lone pairs or bonds. We don t need to worry about all bonds, because we can t push an arrow from a single bond (that would violate the first commandment). So we only care about double or triple bonds. Double and triple bonds are called pi bonds. So we need to look for lone pairs and pi bonds. Usually, only a small region of the molecule will possess either of these features. 

A—Answers B—E contain molecules or ions with double or triple bonds. Double and triple bonds contain Jt bonds. Water has only single (a) bonds. If any are not obvious, draw a Lewis structure. 

In some cases, such as C—O and C—C, the variations can be much greater, approaching 20 percent. In these cases, the values fall into groups which we interpret as representative of single- and multiple bonds double, and triple. 

Again, the reaction sites are multiple bonds (double and triple bonds) polar bonds and Lewis acids (electrophiles) and Lewis bases (nucleophiles). 

Step 1 To determine the name of the electron group geometry around each atom that is attached to two or more other atoms, count the number of electron groups around each central atom and apply the guidelines found on Table 12.3. An electron group can be a single bond, a lone pair, or a multiple bond. (Double and triple bonds count as one group.)... 

As described earlier in this chapter, polymers are long chains of atoms linked together. They may be flexible and bendable. To explain this, one may visual them as ball-and-stick model. In chemistry, the ball-and-stick model is a molecular model of a chemical substance which aims to display both the three-dimensional position of the atoms and the bonds between them. The atoms are typically represented by spheres, connected by rods which represent the bonds. Double and triple bonds are usually represented by two or three curved rods, respectively. The chemical element of each atom is often indicated by the sphere s color and size. The top of Figure 1.6 shows a drawing of a ball-and-stick model of a molecule. Figure 1.6 also indicates that there is free rotation around the single bonds. If there was a double or triple bond, there would not be any rotation possible around those bonds. 

Each N atom appears to have only six outer-shell electrons, not the expected eight. The situation can be corrected by bringing the four unpaired electrons into the region between the N atoms and using them for additional bond pairs. In all, we now show the sharing of three pairs of elecfrons between the N atoms. The bond between the N atoms in N2 is a triple covalent bond (=). Double and triple covalent bonds are known as multiple covalent 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 ... 

Double and triple bonds are counted as if they were split into two or three single bonds, respectively. 

Molecular models such as the one shown often do not explicitly show double and triple bonds Write a Lewis structure for this hydrocarbon showing the location of any multiple bonds Specify the hybndization state of each carbon (You can view this model in more detail on Learn mg By Modeling)... 

Univalent radicals have the endings -enyl, -ynyl, -dienyl, -diynyl, etc. When necessary, the positions of the double and triple bonds are indicated by locants, with the carbon atom with the free valence numbered as 1. Examples ... 

Should there be a choice for the fundamental straight chain of a radical, that chain is selected which contains (1) the maximum number of double and triple bonds, (2) the largest number of carbon atoms, and (3) the largest number of double bonds. These are in descending priority. 

Bivalent radicals derived from unbranched alkenes, alkadienes, and alkynes by removing a hydrogen atom from each of the terminal carbon atoms are named by replacing the endings -ene, -diene, and -yne by -enylene, -dienylene, and -ynylene, respectively. Positions of double and triple bonds are indicated by numbers when necessary. The name vinylene instead of ethenylene is retained for —CH=CH—. 

For purely alicyclic compounds, the selection process proceeds successively until a decision is reached (a) the maximum number of substituents corresponding to the characteristic group cited earliest in Table 1.7, (b) the maximum number of double and triple bonds considered together, (c) the maximum length of the chain, and (d) the maximum number of double bonds. Additional criteria, if needed for complicated compounds, are given in the lUPAC nomenclature rules. 

In presence of carbon-carbon double and triple bonds —C=C—C=C— In presence of two carbon-carbon triple bonds —C=C—C=C— Double bond... 

Dibromoborane—dimethyl sulfide is a more convenient reagent. It reacts directly with alkenes and alkynes to give the corresponding alkyl- and alkenyldibromoboranes (120—123). Dibromoborane differentiates between alkenes and alkynes hydroborating internal alkynes preferentially to terminal double and triple bonds (123). Unlike other substituted boranes it is more reactive toward 1,1-disubstituted than monosubstituted alkenes (124). 

Many other examples ia the Hterature illustrate the possibiUties of chemoselective hydroborations (124,186—189). For example, selectivity between double and triple bonds has been shown (124). 

Unsymmetrical functional tetraorganotins are generally prepared by tin hydride addition (hydrostaimation) to functional unsaturated organic compounds (88) (see Hydroboration). The realization that organotin hydrides readily add to atiphatic carbon—carbon double and triple bonds forming tin—carbon bonds led to a synthetic method which does not rely on reactive organometatiic reagents for tin—carbon bond formation and, thus, allows the synthesis of... 

The addition of nucleophiles to double and triple bond systems is often a convenient way of effecting an intramolecular ring closure. Addition to cyano groups has received considerable attention, as in addition to ring formation it provides a convenient method for the introduction of an amino group. Reaction of methyl Af-cyanodithiocarbimidate with Af-methylaminoacetonitrile resulted in displacement of methanethiol and formation of (314). Sodium ethoxide treatment in DMF converted (314) into a 4-amino-5-cyanoimidazole... 

The hybridization concept can also be applied to molecules containing double and triple bonds. The descriptive valence bond approach to the bonding in ethylene and... 

The earbon-to-hydrogen bond is always a single bond. While the resulting bond between earbon and hydrogen is always a single bond, earbon does have the capability to form double and triple bonds between itself and other carbon atoms, and/or any other atom that has the ability to form more than one bond. When a hydrocarbon contains only single bonds between earbon atoms, it is known as a saturated hydrocarbon when there is at least one double or triple bond between two carbon atoms anywhere in the molecule, it is an unsaturated hydrocarbon. When determining the saturation or unsaturation of a hydrocarbon, only the carbon-to-... 

Double and triple bonded hydrocarbons Fire and explosion... 

Anhydrous hydrogen fluoride adds across carbon-carbon double and triple bonds and to other unsaturated systems, but wide variations of solvent, catalyst, temperature, and conditions are required with different substrates. 

All five models for ethane show roughly the same information. The Wire model looks like a line formula in your chemistry textbook, except that all atoms, not just earbons, are found at the end of a line or at the intersection of lines. (The only exception occurs where three atoms lie on a line. Here, a Wire model will not show the exact position of the center atom.) The Wire model uses color to distinguish different atoms, and one, two and three lines to indicate single, double and triple bonds, respectively. 

The following bond density surface for hex-5-en-l-yne clearly allows you to see whicf atoms are connected. It does not, however, distinguish single, double and triple carbon-carbon bonds as clearly as a simple skeletal model. 

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