Alkynes classification

The alkyne classification follows the same pattern as the alkene classification. The simplest alkyne has two carbons and is named ethyne (formal lUPAC name), or acetylene (common lUPAC name). See Figure 14.16. The name acetylene... 

The classification of hydrocarbons as aliphatic or aromatic took place m the 1860s when It was already apparent that there was something special about benzene toluene and their derivatives Their molecular formulas (benzene is CgHg toluene is C7Hj ) indicate that like alkenes and alkynes they are unsaturated and should undergo addition reac tions Under conditions m which bromine for example reacts rapidly with alkenes and alkynes however benzene proved to be inert Benzene does react with Bi2 m the pres ence of iron(III) bromide as a catalyst but even then addition isn t observed Substitu tion occurs instead ... 

We will begin with a brief discussion of the physical and spectroscopic properties of alkenes and alkynes. But the major emphasis in the chapter is on two main types of reactions, ionic addition and radical-chain addition. For ionic additions we will make extensive use of the classification of reagents as electrophiles and nucleophiles, as described in Chapter 8. 

The cycloaddition of phospholes with alkynes to synthesize phosphorins comes under this classification. For phosphorins to form, the transient 2H-phosphole has to react with alkynes followed by elimination of a carbene. This type of synthetic approach is less common and is discussed in the earlier chapter <1996CHEC-II(5)639>. 

Another means of classification depends on the type of bonding that exists between carbons. Hydrocarbons which contain only carbon-to-carbon single bonds are called alkanes. These are also referred to as saturated molecules. Hydrocarbons containing at least one carbon-to-carbon double bond are called alkenes, and those compounds with at least one carbon-to-carbon triple bond are called alkynes. These are compounds that are referred to as unsaturated molecules. Finally, a class of cyclic hydrocarbons that contain a closed loop (sextet) of electrons are called aromatic (see Chapter 14 in your text for further details). Table 28.1 distinguishes between the families of hydrocarbons. 

Metal compounds are often used to stabilize reactive organic fragments via complexation and intriguing alkyne ligand in this classification is benzyne. A series of iridium benzyne complexes has been made with compound (44) as an example and the reaction chemistry of coordinated benzyne has been explored. ... 

Conventional texts on organic chemistry are usually divided into chapters corresponding to compound types, chemical reactions, synthetic methods, etc. From the viewpoint of synthesis, this traditional classification should be supplemented by consideration of the specific aspects of synthetic relationships i.e. into what a given compound can be converted and from what it can be obtained, in other words, its place in the solution of synthetic tasks. For example, in accordance with conventional classification, alkenes, alkynes, cyclopropanes, and oxiranes fall into substantially different and rather distant taxons of organic chemistry systematics. These classes traditionally are treated as independent and only remotely related areas of organic chemistry. However,... 

Such structure reactions have existed in organic chemistry since long. Wilson gives an example of classification of electrophilic addition reactions of alkenes and alkynes. Patterns in organometalhc chemistry with applications in organic synthesis have been discussed by Schwartz and Labinger. 

Palladium-catalyzed reactions have been widely investigated and have become an indispensable synthetic tool for constructing carbon-carbon and carbon-heteroatom bonds in organic synthesis. Especially, the Tsuji-Trost reaction and palladium(II)-catalyzed cyclization reaction are representative of palladium-catalyzed reactions. These reactions are based on the electrophilic nature of palladium intermediates, such as n-allylpalladium and (Ti-alkyne)palladium complexes. Recently, it has been revealed that certain palladium intermediates, such as bis-7i-allylpalladium, vinylpalladium, and arylpalladium, act as a nucleophile and react with electron-deficient carbon-heteroatom and carbon-carbon multiple bonds [1]. Palladium-catalyzed nucleophilic reactions are classified into three categories as shown in Scheme 1 (a) nucleophilic and amphiphilic reactions of bis-n-allylpalladium, (b) nucleophilic reactions of allylmetals, which are catalytically generated from n-allylpalladium, with carbon-heteroatom double bonds, and (c) nucleophilic reaction of vinyl- and arylpalladium with carbon-heteroatom multiple bonds. According to this classification, recent developments of palladium-catalyzed nucleophilic reactions are described in this chapter. 

Dihydroxyethylaniline N,N-Di-(2-hydroxyethyl) aniline N,N-Di(P-hydroxyethyl) aniline. See Phenyidiethanolamine Di-(2-hydroxyethyl) butynediol CAS 1606-85-5 EINECS/ELINCS 216-526-0 Synonyms 1,4-Bis (2-hydroxyethoxy)-2-butyne 2,2 -(2-Butyne-1,4-diylbis (oxy)) bisethanol 1,4-Di-(2-hydroxyethoxy) but-2-yne Ethanol, 2,2 -(2-butyne-1,4-diylbis (oxy)) bis- Ethanol, 2,2 -(2-butynylenedioxy) di-Classification Alkyne Empirical C8H14O4... 

Classification Alkynes Empirical C6H10O2 Formula CHaCHOHC CCHOHCHa Properties Solid m.w. 114.15 dens. 1.009 m.p. 

In most of the palladium-catalysed domino processes known so far, the Mizoroki-Heck reaction - the palladium(0)-catalysed reaction of aryl halides or triflates as well as of alkenyl halides or triflates with alkenes or alkynes - has been apphed as the starting transformation accordingly to our classification (Table 8.1). It has been combined with another Mizoroki-Heck reaction [6] or a cross-coupling reaction [7], such as Suzuki, Stille or Sonogashira reactions. In other examples, a Tsuji-Trost reaction [8], a carbonylation, a pericyclic or an aldol reaction has been employed as the second step. On the other hand, cross-couphng reactions have also been used as the first step followed by, for example, a Mizoroki-Heck reaction or Tsuji-Trost reactions, palladation of alkynes or allenes [9], carbonylations [10], aminations [11] or palladium(II)-catalysedWacker-type reactions [12] were employed as the first step. A novel illustrative example of the latter procedure is the efficient enantioselective synthesis of vitamin E [13]. 

Hydrocarbons are compounds composed entirely of carbon and hydrogen atoms bonded to each other by covalent bonds. These molecules are further classified as saturated or unsaturated. Saturated hydrocarbons have only single bonds between carbon atoms. These hydrocarbons are classified as alkanes. Unsaturated hydrocarbons contain a double or triple bond between two carbon atoms and include alkenes, alkynes, and aromatic compounds. These classifications are summarized in Figure 19.3. 

In Chapter 11 of Part A, the mechanistic classification of 1,3-dipolar cycloadditions as a type of concerted cycloadditions was developed. Dipolar cycloaddition reactions are useful both for the synthesis of heterocyclic compounds and for carbon-carbon bond formation. Table 6.2 lists some of the types of molecules that are capable of dipolar cycloaddition. These molecules, which are called 1,3-dipoles, have r-electron systems that are isoelectronic with allyl anion, consisting of two filled and one empty orbital. Each molecule has at least one charge-separated resonance structure with opposite charges in a 1,3-relationship. It is this structural feature that leads to the name 1,3-dipolar cycloadditions for this class of reactions. The other reactant in a dipolar cycloaddition, usually an alkene or alkyne, is referred to as the dipolarophile. Other multiply bonded functional groups such as imine, azo, and nitroso groups can also act as dipolarophiles. The transition states for 1,3-dipolar cycloadditions involve four tc electrons fi om the 1,3-dipole and two from the dipolarophile. As in the Diels-Alder reaction, the reactants approach one another in parallel planes. 

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