Alkenes 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... 

We will show here the classification procedure with a specific dataset [28]. A reaction center, the addition of a C-H bond to a C=C double bond, was chosen that comprised a variety of different reaction types such as Michael additions, Friedel-Crafts alkylation of aromatic compounds by alkenes, or photochemical reactions. We wanted to see whether these different reaction types can be discerned by this... 

A rational classification of reactions based on mechanistic considerations is essential for the better understanding of such a broad research field as that of the organic chemistry of Pd. Therefore, as was done in my previous book, the organic reactions of Pd are classified into stoichiometric and catalytic reactions. It is essential to form a Pd—C cr-bond for a synthetic reaction. The Pd— C (T-bond is formed in two ways depending on the substrates. ir-Bond formation from "unoxidized forms [1] of alkenes and arenes (simple alkenes and arenes) leads to stoichiometric reactions, and that from oxidized forms of alkenes and arenes (typically halides) leads to catalytic reactions. We first consider how these two reactions differ. 

Reactions of another class are catalyzed by Pd(II) compounds which act as Lewis acids, and are treated in Chapter 5 and partly in Chapter 4. From the above-mentioned explanation, the reactions catalyzed by Pd(0) and Pd(II) are clearly different mechanistically. In this book the stoichiometric and catalytic reactions are classified further according to reacting substrates. However, this classification has some problems, viz. it leads to separate treatment of some unit reactions in different chapters. The carbonylation of alkenes is an example. Oxidative carbonylation of alkenes is treated in Chapter 3 and hydrocar-bonylation in Chapter 4. 

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 ... 

CLASSIFICATION OF REACTIONS BY TYPE OF COMPOUND SYNTHESIZED 16-47 Reaction of phosphines with Michael alkenes or with alkyl halides... 

Carbene reactivity is strongly affected by substituents.117 Various singlet carbenes have been characterized as nucleophilic, ambiphilic, and electrophilic as shown in Table 10.2 This classification is based on relative reactivity toward a series of both nucleophilic alkenes, such as tetramethylethylene, and electrophilic ones, such as acrylonitrile. The principal structural feature that determines the reactivity of the carbene is the ability of the substituent to act as an electron donor. For example, dimethoxycarbene is devoid of electrophilicity toward alkenes because of electron donation by the methoxy groups.118... 

FIGURE 6.2 Representation of multivariate data by icons, faces, and music for human cluster analysis and classification in a demo example with mass spectra. Mass spectra have first been transformed by modulo-14 summation (see Section 7.4.4) and from the resulting 14 variables, 8 variables with maximum variance have been selected and scaled to integer values between 1 and 5. A, typical pattern for aromatic hydrocarbons B, typical pattern for alkanes C, typical pattern for alkenes 1 and 2, unknowns (2-methyl-heptane and meta-xylene). The 5x8 data matrix has been used to draw faces (by function faces in the R-library Tea-chingDemos ), segment icons (by R-function stars ), and to create small melodies (Varmuza 1986). Both unknowns can be easily assigned to the correct class by all three representations. 

Table 10.2. Classification of Carbenes on the Basis of Reactivity toward Alkenes ...

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. 

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. 

The structure of the sex pheromone for the Fucus species, fucoserratene (11), was elucidated in 1973.16 The positions and geometries of alkenes were revealed by comparison of the gas chromatographic behavior with those of the isomeric conjugated 1,3,5- and 2,4,6-octatrienes. To date, a series of hydrocarbons and epoxides 1-11 and their stereoisomers have been identified within the pheromone bouquets of more than 100 different species of brown algae.17-23 Identification of these compounds was based on a combination of gas chromatography-mass spectrometry (GC-MS) analysis and by comparison with authentic synthetic compounds. These sex pheromones were all lipophilic, volatile compounds that consisted of C8 or Cn linear or monocyclic hydrocarbons or their epoxides. The monocyclic compounds have a cyclopropane, cyclopentene, or cyclo-heptadiene structure. Interestingly, the relationships between the chemical structures of pheromones and the taxonomical classifications of algae are unclear (Table 1). 

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