Isolated double or triple bonds

On the other hand, if two atoms in a molecule are connected by a significantly stronger covalent bond then the other covalent bonds of the molecule (e.g., the isolated double or triple bond, as in one of the cases >C=C<, >C=0, >C=N-, -N=N-, -C-C-), than the vibration of the respective bond can be also considered quasi-independent from the oscillation of the rest of the molecule. In this case, we can say that in one of the normal modes of vibration of the molecule practically occurs only the elongation oscillation of that bond, so the optical absorption band, generated in the IR spectrum by the normal mode of vibration, is characteristic for the presence of that covalent bond... 

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. 

One obvious synthetic route to isoxazoles and dihydroisoxazoles is by [3+2] cycloadditions of nitrile oxides with alkynes and alkenes, respectively. In the example elaborated by Giacomelli and coworkers shown in Scheme 6.206, nitroalkanes were converted in situ to nitrile oxides with 1.25 equivalents of the reagent 4-(4,6-di-methoxy[l,3,5]triazin-2-yl)-4-methylmorpholinium chloride (DMTMM) and 10 mol% of N,N-dimethylaminopyridine (DMAP) as catalyst [373], In the presence of an alkene or alkyne dipolarophile (5.0 equivalents), the generated nitrile oxide 1,3-dipoles undergo cycloaddition with the double or triple bond, respectively, thereby furnishing 4,5-dihydroisoxazoles or isoxazoles. For these reactions, open-vessel microwave conditions were chosen and full conversion with very high isolated yields of products was achieved within 3 min at 80 °C. The reactions could also be carried out utilizing a resin-bound alkyne [373]. For a related example, see [477]. 

In a few cases [4 + 2]-cycloaddition reactions of 1,2,4-triazines with C—N double or triple bonds have been reported. Thus, benzimidamide reacts with 1,2,4-triazines in refluxing toluene to yield 1,3,5-triazines 30 (see Section 2.3.1.2.3.). The isolated products are rationalized by assuming that the dienophile undergoes addition to the 2- and 5-positions of the 1,2,4-triazines, as in the reactions with ynamines, then a nitrile R CN is eliminated followed by aromatization via loss of ammonia.367,459... 

Isolated carbon-carbon double or triple bonds do not usually take part in inter-molecular Diels-Alder reactions, but a number of cyclic alkenes and alkynes with pronounced angular strain are reactive dienophiles. The driving force for these reactions is thought to be the reduction in angular strain associated with the transition state for the addition. Thus, cyclopropene reacts rapidly and stereoselectively with cyclopentadiene at 0°C to form the endo adduct 7 in 97% yield, and butadiene gives norcarene 8 in 37% yield (3.13). ... 

A number of metal hydrides have been employed as reducing agents in organic chemistry, but the most commonly used are lithium aluminium hydride and sodium borohydride, both of which are commercially available. These reagents are nucleophilic and as such they normally attack polarized multiple bonds such as C=0 or C=N by transfer of hydride ion to the more-positive atom. They do not usually reduce isolated carbon-carbon double or triple bonds. 

Of the partner molecules indicated in Scheme 1 only a few representatives (boxed) are discussed. As far as compounds with carbon-carbon double or triple bonds are concerned, one can differentiate between three subgroups those with isolated, conjugated, or aromatic (a) systems. 

Selenenamides (23) are obtained by the substitution of selenenyl halides with amines or by the metathesis of the former compounds with Af-silylamines. N-(Phenylseleno)phthalimide (24) is similarly obtained using potassium phthalimide (Scheme 10). These compounds can be isolated but are prone to hydrolyze when exposed to moisture. Selenenamides react with aldehydes or jS-dicarbonyl compounds to afford a-seleno derivatives (as in the process shown in equation 11), and add to activated double and triple bonds, as in the example in equation (19). The imide (24) is a useful alternative to PhSeCl in various selenenylation reactions, and to ArSeCN in the conversion of alcohols and carboxylic acids to selenides and selenoesters (8), as shown in Scheme 3. 

Additionally, classes (or types) of hydrocarbons were, and still are, determined based on the capability to isolate them by separation techniques. The four fractional types into which petroleum is subdivided are paraffins, olefins, naphthenes, and aromatics (PONA). Paraffinic hydrocarbons include both normal and branched alkanes, whereas olefins refer to normal and branched alkenes that contain one or more double or triple carbon-carbon bonds. Naphthene (not to be confused with naphthalene) is a term specific to the petroleum industry that refers to the saturated cyclic hydrocarbons (cycloalkanes). Finally, the term aromatics includes all hydrocarbons containing one or more rings of the benzenoid structure. 

---