Naming the Alkynes

A carbon-carbon triple bond is the functional group characteristic of the alkynes. The general formula for the alkynes is C H2 2, the same as that for the cycloalkenes. The common names for many alkynes are still in use, including acetylene, the common name of the smallest aUcyne, C2H2. Other alkynes are treated as its derivatives—for example, the alkylacetylenes. 

The lUPAC rules for naming alkenes (Section 11-1) also apply to alkynes, the ending -yne replacing -ene. A number indicates the position of the triple bond in the main chain. 

Alkynes having the general structure RC=CH are terminal, whereas those with the structure of RC=CR are internal. 

Substituents bearing a triple bond are alkynyl groups. Thus, the substituent -C=CH is named ethynyl its homolog -CH2C=CH is 2-propynyl (propargyl). Like alkanes and alkenes, alkynes can be depicted in straight-line notation. 

In lUPAC nomenclature, a hydrocarbon containing both double and triple bonds is called an alkenyne. The chain is numbered starting from the end closest to either of the functional groups. When a double bond and a triple bond are at equidistant positions fiom either terminus, the double bond is given the lower number. Alkynes incorporating the hydroxy function are named alkynols. Note the omission of the final e of -ene in -enyne and of -yne in -ynol. The OH group takes precedence over both double and triple bonds in the numbering of a chain. 

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As a result of this process, the sequential addition of a carbon nucleophile and a carbon electrophile across a triple bond is achieved. For example, addition of cuprate 101 (Scheme 2.32) across the triple bond of acetylene produces the vinylcuprate intermediate 102. Quenching of the latter with electrophile 103 gave acetoxydiene 104, the active constituent of the pheromone Cossus cossus. The sequence exemplified in Scheme 2.32 enables independent variations in the structure of all participants involved, namely the alkyne, the organome-tallic nucleophile, and the electrophile. Therefore this approach can serve as a unified protocol for the one-pot assemblage of various alkenes from simple precursors. 

A gaseous alkyne is burned completely in oxygen. The volume of the water vapor that forms equals the volume of the alkyne burned (the volumes are measured at the same temperature and pressure). Name the alkyne and write a balanced equation for its combustion. 

Problem 7.6 One of the intermediate compounds in the synthesis of the spruce budworm sex pheromone is (.E)- 1-tetradecen-l-ol. How can this compound be produced from a substituted alkyne Name the alkyne. 

There also exists an acidregioselective condensation of the aldol type, namely the Mannich reaction (B. Reichert, 1959 H. Hellmann, 1960 see also p. 291f.). The condensation of secondary amines with aldehydes yields Immonium salts, which react with ketones to give 3-amino ketones (=Mannich bases). Ketones with two enolizable CHj-groupings may form 1,5-diamino-3-pentanones, but monosubstitution products can always be obtained in high yield. Unsymmetrical ketones react preferentially at the most highly substituted carbon atom. Sterical hindrance can reverse this regioselectivity. Thermal elimination of amines leads to the a,)3-unsaturated ketone. Another efficient pathway to vinyl ketones starts with the addition of terminal alkynes to immonium salts. On mercury(ll) catalyzed hydration the product is converted to the Mannich base (H. Smith, 1964). 

The skeletal rearrangement of various strained cyclic compounds is carried out with a catalytic amount of soluble complexes of PdCl2. Namely, the rearrangements of bulvalene (67) to bicyclo[4.2.2]deca-2,4,7,9-tetraene (68)[54], cubane (69) to cuneane (70)[55], hexamethyl Dewar benzene (71) to hexa-methylbenzene (72)[56], and 3-oxaquadricyclanes[57] and quadricyclane (73) to norbornadiene[58-60] take place mostly at room temperature. Reaction of iodocubane (74) with a terminal alkyne catalyzed by Pd(0) and CuBr unexpectedly affords an alkynylcyclooctatetraene 75, without giving the desired cubylalkyne 76. Probably the rearrangement is a Pd-catalyzed reaction[61]. 

Wnte structural formulas and give the lUPAC names for all the alkynes of molecular for mula CgHiQ... 

Eor multiple unsaturated bonds, the chain is so numbered as to give the lowest possible locants to the unsaturated bonds. When there is a choice in numbering, the double bonds are given the lowest locants, and the alkene is cited before the alkyne where both occur in the name. Examples ... 

Alkenes and alkynes are similar in structure to the alkanes except the alkenes contain a carbon-to-carbon double bond (C=C) and the alkynes contain a carbon-to-carbon triple bond (C=C). The name prefixes are exactly the same as for the alkanes with the same number of carbons, but the endings are -one for compounds with double bonds and their derivatives and -yne for compounds with triple bonds... 

Another analogous series of unsaturated hydrocarbons that contain just one multiple bond, but, instead of being a double bond, it is a triple bond is the alkynes. The names of all the compounds end in -yne. The only compound m this series that is at all common happens to be an extremely hazardous material. It is a highly unstable (to heat, shock, and pressure), highly flammable gas that is the first compound in the series. This two-carbon unsaturated hydrocarbon with a triple bond between its two carbon atoms is called ethyne, and indeed this is its proper name. It is, however, known by its common name, acetylene. 

Two new sections on the protection of phosphates and the alkyne-CH are included. All other sections of the book have been expanded, some more than others. The section on the protection of alcohols has increased substantially, reflecting the trend of the nineties to synthesize acetate- and propionate-derived natural products. An effort was made to include many more enzymatic methods of protection and deprotection. Most of these are associated with the protection of alcohols as esters and the protection of carboxylic acids. Here we have not attempted to be exhaustive, but hopefully, a sufficient number of cases are provided that illustrate the true power of this technology, so that the reader will examine some of the excellent monographs and review articles cited in the references. The Reactivity Charts in Chapter 10 are identical to those in the first edition. The chart number appears beside the name of each protective group when it is first introduced. No attempt was made to update these Charts, not only because of the sheer magnitude of the task, but because it is nearly impossible in... 

Name the following alkynes, and predict the products of their reaction with (i) H2 in the presence of a Lindlar catalyst and (ii) HsO" " in the presence of HgSC ... 

The IUPAC names of alkynes are derived from those of the corresponding alkenes by replacing the suffix -ene with -yne. Thus we have... 

The alkynes are hydrocarbons that have at least one carbon-carbon triple bond. The simplest is ethyne, FIO CH, which is commonly called acetylene (20). Alkynes are named like the alkenes but with the suffix -yne. 

A few remarkable, but rather uncommon, transfer hydrogenations also deserve mention within the context of this chapter namely, the reduction of alkynes to alkenes using a chromium catalyst, and the reduction of double bonds using diimines. 

Hydrocarbons that contain one or more carbon-to-carbon triple bonds are called alkynes. The names of alkynes end in -yne. Ethyne, commonly known as acetylene, is the simplest alkyne. It consists of two carbon atoms with a triple bond between them, with each carbon also bonded to one hydrogen atom. The chemical formula for ethyne is C2H2. 

Alkynes are hydrocarbons that contain a carbon-carbon triple bond. A triple bond consists of a cr bond and two tt bonds. The general formula for the alkynes is C li2n-2- The triple bond possesses two elements of unsaturation. Alkynes are commonly named as substituted acetylenes. Compounds with triple bonds at the end of a molecule are called terminal alkynes. Terminal —CH groups are called acetylenic hydrogens. If the triple bond has two alkyl groups on both sides, it is called an internal alkyne. 

Another analogous series of unsaturated hydrocarbons that contain just one multiple bond, but, instead of being a double bond, it is a triple bond is the alkynes. The names of all die compounds... 

Consideration of the oxidation level reveals diat while one carbon is reduced (the one to which hydrogen adds), die other is oxidized (die one to which the oxygen adds). There is no net change in oxidation level of the alkene functional group. Likewise die reverse processes of these addition reactions, namely, elimination of HX from alkyl halides and dehydration of alcohols to give alkenes, are not redox processes. Additions of water to alkynes is analogous. In this case, however, the product is a ketone, the oxidation level of the ketone is seen to be the same as the alkyne, and so no net change in oxidation level has occurred. 

Table 5.1 lists the names and formulas of the first 10 unbranched (sometimes called normal) alkanes, alkenes, and alkynes. Photocopy and distribute this table to students. As students study this table, they should look for relationships between the number of carbon atoms and the number of hydrogen atoms in the various hydrocarbons. They will soon discover that the general formula for alkanes is CnH2n+2, the general formula for alkenes is c h2 , and the general formula for the alkynes is C H2n 2. 

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