Hydrocarbonation alkynes

Now consider the alkynes, hydrocarbons with carbon-carbon triple bonds. The Lewis structure of the linear molecule ethyne (acetylene) is H—O C- H. To describe the bonding in a linear molecule, we need a hybridization scheme that produces two equivalent orbitals at 180° from each other this is sp hybridization. Each C atom has one electron in each of its two sp hybrid orbitals and one electron in each of its two perpendicular unhybridized 2p-orbitals (43). The electrons in the sp hybrid orbitals on the two carbon atoms pair and form a carbon—carbon tr-bond. The electrons in the remaining sp hybrid orbitals pair with hydrogen Ls-elec-trons to form two carbon—hydrogen o-bonds. The electrons in the two perpendicular sets of 2/z-orbitals pair with a side-by-side overlap, forming two ir-honds at 90° to each other. As in the N2 molecule, the electron density in the o-bonds forms a cylinder about the C—C bond axis. The resulting bonding pattern is shown in Fig. 3.23. 

The metal-oxo molecular models outlined above have a quite remarkable potential for studying the metal activity in a quite unusual environment. Some of the possibilities could be (1) the generation and the chemistry of M—C, M=C, M=C functionalities (2) the interaction with alkenes, alkynes, hydrocarbons, and hydrogen (3) the activation of small molecules like N26 and CO (4) the support of metal-metal bonded functionalities and (5) the generation of highly reactive low-valent metals. 

Alkynes hydrocarbons containing at least one carbon-carbon triple bond. 

Our discussion has centered around hydrocarbon molecules that consist of carbon atoms bonded to each other in long chains. These chains are called normal, straight, or unbranched. The chains may have only single bonds (alkanes), double bonds (alkenes), or triple bonds (alkynes). Hydrocarbons with only single bonds are called saturated hydrocarbons with double or triple bonds are called unsaturated. Not all hydrocarbons want to form straight chains. After all, who among us wants to be straight and serious all the time Some of us will always be comedians. In the world of hydrocarbon molecules, the comedians are the branched and cyclic molecules. 

We classify hydrocarbons according to their bonding (Section 2-12), as shown in Table 3-1. Alkanes have only single bonds. A hydrocarbon with a carbon-carbon double bond (such as ethylene) is an alkene. If a hydrocarbon has a carbon-carbon triple bond (like acetylene), it is an alkyne. Hydrocarbons with aromatic rings (resembling benzene) are called aromatic hydrocarbons. 

Elimination reactions introduce n bonds into organic compounds, so they can be used to synthesize alkenes and alkynes—hydrocarbons that contain one and two n bonds, respectively. Like nucleophilic substitution, elimination reactions can occur by two different pathways, depending on the conditions. By the end of Chapter 8, therefore, you will have learned four different organic mechanisms, two for nucleophilic substitution (SnI and Sn2) and two for elimination (El and E2). 

Ethynylestradiol is a synthetic compound whose structure closely resembles the carbon skeleton of female estrogen hormones. Because it is more potent than its naturally occurring anaiogues, it is a component of several widely used oral contraceptives. Ethynylestradiol and related compounds with similar biological activity contain a carbon-carbon triple bond. In Chapter 11 we learn about alkynes, hydrocarbons that contain triple bonds. 

A Lewis acid catalyst can interact with the reagent containing a functional group having a donor atom with nonbonded pairs of electrons. This gives rise to a positively polarized complex or a carbocationic species, which then reacts with the -rr-donor substrate (aromatic, alkenic or alkynic hydrocarbons). Though this process can occur under strictly anhydrous conditions, this generally is not the case as impurity, moisture, or other cocatalysts are usually present. In the case of reactions of alkenes and alkynes... 

Alkynes Hydrocarbons that have one or more carbon-carbon triple bonds. 

Alkynes. Hydrocarbons that contain one or more carbon-carbon triple bonds. They have the general formula C H2 - 2> where n = 2,3,. (24.2) Allotropes. Two or more forms of the same element that differ significantly in chemical and physical properties. (2.6) Alloy. A solid solution composed of two or more metals, or of a metal or metals with one or more nonmetals. (20.2) Alpha particles. See alpha rays. 

Chapter 6 covers the reactions of alkynes—hydrocarbons that contain carbon-carbon triple bonds. Because alkenes and alkynes both have reactive carbon-carbon tt bonds, you will discover that their reactions have many similarities. This chapter will also introduce you to some of the techniques chemists use to design syntheses of organic compounds, and you will then have your first opportunity to design a multistep synthesis. 

It has been evidenced that among the various unsaturated hydrocarbons, alkynes show the largest inhibiting effect on all oxido-reduction reactions occuring on a PtRh catalyst, i.e. non-alkyne hydrocarbons, CO and NO are not converted until alkynes are eliminated,... 

Marine organisms are a rich source of exotic polyalkynes many of which possess structures not found in terrestrial species in addition to conventional acyclic allene-alkyne hydrocarbons and their simple derivatives. For example, red algae (in particular of the Laurencia and Phacelocarpus genera) accumulate compounds such as 23-26 " in which bromine derived by enzymic oxidation of Br from the environment is incorporated... 

The alkyne hydrocarbons have at least one triple bond between the carbons in the chain. The ending for the alkyne family is yne. Alkynes are unsaturated, with the... 

Most of the alkane, alkene, and alkyne hydrocarbon compounds are considered to be flammable as their major hazard, and the toxicity is considered as moderate to low. The vapors are more likely to be asphyxiant than toxic. TLVs range from 50 ppm for hexane to 300 ppm for octane. Decane is listed as having a narcotic effect. Many of these hydrocarbons are found in mixtures, and it will be necessary to look at the Material Safety Data Sheets (MSDS) to obtain toxicity information on particular mixtures. Benzene, toluene, and xylene are aromatic hydrocarbons. They are considered highly toxic and human carcinogens. Benzene has a TLV of 0.1 ppm in air, according to the NIOSH Guide 1997 Addition, and an STEL of 1 ppm. The OSHA STEL is 5 ppm and a PEL of 1 ppm. Toluene is toxic by ingestion, inhalation, and skin absorption. The TLV for toluene is 100 ppm in air. Xylenes are toxic by... 

Wu Y-T, Huang K-H, Shin C-C, Wu T-C (2008) Palladium-catalyzed formation of highly substituted naphthalenes from arene and alkyne hydrocarbons. Chem-Eur J 14 6697-6703. doi 10.1002/aSSN)1521 -3765... 

Alkenes Hydrocarbons with Double Bonds 469 Alkynes Hydrocarbons with Triple Bonds 470... 

Chapter 4 examines the group frequencies of triple bonds and cumulated double bonds. The alkyne hydrocarbons (acetylenes, —C=C—) are treated in I and the important nitrile group, —C=N, in detail in II. In the case of the alkynes the amount and type of substitution can often be identified from vibrational data (I, D, E). Systems containing cumulative double bonds (so-called back-to-back double bonds, >C=C=C<) such as the allenes in the hydrocarbon series are considered in III. A number of them contain hetero-atoms as for example, the ketenes (>C=C=0, III, B). Section F presents a problem that allows the reader to determine which of two possible structures is the correct one based on infrared and Raman data. 

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