Alkynes Hydrocarbons Containing Triple Bonds

Hydrocarbons containing a triple bond are described as alkynes (old name acetylenes). The first member of the class, H-C=C-H, is ethyne, and the suffix for this class is -yne. The old name for ethyne is acetylene, and this will doubtless continue to be used as long as we use oxyacetylene welding and cutting equipment. As usual, we start with the configuration of carbon 

11 The condensed method of writing this formula is not as informative as a stick diagram, so first convert it to that, number the structure so that the triple bond has the lowest number, then add the substituents. 

12 First, draw and number 1-heptyne, then add the substituent  

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We have seen that there are three classes of hydrocarbons alkanes, which contain only single bonds alkenes, which contain double bonds and alkynes, which contain triple bonds. We examined the chemistry of alkenes in Chapter 4 and the chemistry of alkynes in Chapter 6. Now we will take a look at the chemistry of alkanes. 

Acetylene, H—C=C—H, is the first member of a homologous series of hydrocarbons containing triple bonds. Aside from acetylene, these substances (called alkynes) have not found wide use, except for the manufacture of other chemicals. 

Diynes and triynes refer to alkynes containing two or three triple bonds poly-ynes contain multiple triple bonds. A conjugated triyne is a straight-chain hydrocarbon with triple bonds alternating with single bonds. An examples is... 

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

The above discussions have concentrated on hydrocarbons, both saturated and unsaturated, with the unsaturated hydrocarbons containing only one multiple bond. The unsaturated hydrocarbons are the alkenes with one double bond and the alkynes with one triple bond. There are other straight-chain hydrocarbons that are unsaturated containing more than one multiple bond, some with more than one double bond, and some with a mixture of double bonds and triple bonds. The combinations and permutations are endless, but there are only a few of the highly unstable materials. 

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. 

The third class of hydrocarbons is the alkynes, which contain at least one triple bond between two carbon atoms. The simplest alkyne is ethyne, C2H2, which is shown in Figure 4. The general formula for an alkyne with one triple bond is C H2 2. 

Alkynes are hydrocarbons that contain a carbon-carbon triple bond. A triple bond can be thought of as a cylinder of electrons wrapped around the a bond. The functional group suffix of an alkyne is yne. A terminal alkyne has the triple bond at the end of the chain an internal alkyne has the triple bond located elsewhere along the chain. Internal alkynes, with two alkyl substituents bonded to the sp carbons, are more stable than terminal alkynes. We now have seen that alkyl groups stabilize alkenes, alkynes, carbo-cations, and alkyl radicals. 

Alkynes The alkynes are a homologous series of hydrocarbons containing a triple bond. The triple bond is formed from one cr bond and two tt bonds. The bond is rigid and allows no rotation. Alkynes with one triple bond have the formula C H2 . The... 

Because alkanes have only single bonds, they contain the largest possible number of hydrogen atoms per carbon atom. As a result, they are called saturated hydrocarbons. Alkenes, alkynes, and aromatic hydrocarbons contain multiple bonds (double, triple, or delocalized tr bonds). As a result, they contain less hydrogen than an alkane with the... 

The alkynes, or acetylenic hydrocarbons, contain one or more carbon-carbon triple bonds, — C = C —. The acyclic alkynes with one triple bond per molecule have the general formula C H2B-2.The bonding in all alkynes is similar to that in acetylene (see Section 8-15). Triply bonded carbon atoms are jp-hybridized. The triply bonded atoms and their adjacent atoms lie on a straight line (Figure 23-10). 

Hydrocarbons can be categorized into three types based on the bonds they contain alkanes contain single bonds, alkenes contain double bonds, and alkynes contain triple bonds. 

Alkynes An unsaturated hydrocarbon that contains one or more triple bonds between carbon atoms is called an alkyne. Alkynes with one triple bond have the general formula C H2 2. The simplest alkyne is ethyne (C2H2), which is commonly called acetylene. The next simplest alkyne is propyne (C3H4). Their condensed structural formulas are shown below. 

A straight- or branched-chain alkane, with formula C H2 +2, has the maximum number of H atoms possible for its number of C atoms. In other classes of hydrocarbons, compounds with the same number of C atoms but fewer H atoms, the C atoms must join into rings, form carbon-to-carbon multiple bonds, or do both to ensure that each C atom forms a total of four bonds. We have already discussed some aspects of ring structures (in Section 26-3). In this section, we focus on hydrocarbons whose molecules contain some double or triple bonds between C atoms. Such molecules are said to be unsaturated. If the molecule has one double bond, the hydrocarbons are the simple alkenes, or olefins they have the general formula C H2 . Simple alkynes have one triple bond in their molecules and have the general formula C H2n-2-... 

Carbon can also form multiple bonds with other carbon atoms. This results in unsaturated hydrocarbons such as olefins (alkenes), containing a carbon-carbon double bond, or acetylenes (alkynes), containing a carbon-carbon triple bond. Dienes and polyenes contain two or more unsaturated bonds. 

Hydrocarbons that contain a carbon-carbon triple bond are called alkynes Non cyclic alkynes have the molecular formula C H2 -2 Acetylene (HC=CH) is the simplest alkyne We call compounds that have their triple bond at the end of a carbon chain (RC=CH) monosubstituted or terminal alkynes Disubstituted alkynes (RC=CR ) have internal triple bonds You will see m this chapter that a carbon-carbon triple bond is a functional group reacting with many of the same reagents that react with the double bonds of alkenes... 

Alkynes are hydrocarbons that contain a carbon-carbon triple bond Sim pie alkynes having no other functional groups or rings have the general formula C H2 -2 Acetylene is the simplest 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 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. 

An alkyne is a hydrocarbon that contains a carbon-carbon triple bond. Acetylene.. H—C= C—H, the simplest alkyne, was once widely used in industry as the starting material for the preparation of acetaldehyde, acetic acid, vinyl chloride, and other high-volume chemicals, but more efficient routes to these substances using ethylene as starting material are now available. Acetylene is still used in the preparation of acrylic polymers but is probably best known as the gas burned in high-temperature oxy-acetylene welding torches. 

An alkyne is a hydrocarbon that contains a carbon-carbon triple bond. Alkyne carbon atoms are sp-hybridized, and the triple bond consists of one sp-sp a bond and two p-p tt bonds. There are relatively few general methods of alkyne synthesis. Two good ones are the alkylation of an acetylide anion with a primary-alkyl halide and the twofold elimination of HX from a vicinal dihalide. 

Alkyne (Chapter 8 introduction) A hydrocarbon that contains a carbon-carbon triple bond, RC CR. 

Nonaromatic hydrocarbons that do not contain such a ring system. Included here are alkanes, which are fully saturated hydrocarbons alkenes, which contain one or more double bonds and alkynes, which contain one or more triple bonds. 

In our study of the simple hydrocarbons, there are only two functional groups. One is a carbon-to-carbon double bond. Hydrocarbons that contain a carbon-to-carbon double bond are alkenes. The other hydrocarbon functional group is a carbon-to-carbon triple bond. Hydrocarbons that contain a triple bond are alkynes. These functional groups are the reactive sites in the alkenes and alkynes. The result is that alkenes and alkynes are more reactive than the alkanes. 

Scientists classify hydrocarbons as either aliphatic or aromatic. An aliphatic hydrocarbon contains carbon atoms that are bonded in one or more chains and rings. The carbon atoms have single, double, or triple bonds. Aliphatic hydrocarbons include straight chain and cyclic alkanes, alkenes, and alkynes. An aromatic hydrocarbon is a hydrocarbon based on the aromatic benzene group. You will encouter this group later in the section. Benzene is the simplest aromatic compound. Its bonding arrangement results in special molecular stability. 

Once again, each carbon has exactly four bonds. Of course, the triple bond between carbons allows each carbon to bond to only one more atom. In acetylene, the single bond is to hydrogen, but in other alkynes, the single bond is to another carbon. Table 6-3 compares 3 hydrocarbons that contain the same number of carbon atoms. 

Alkenes and alkynes are unsaturated hydrocarbons. Alkenes contain at least one carbon-carbon double bond and alkynes have at least one carbon-carbon triple bond. The names of alkenes and alkynes use the alkane prefixes, but add ene and yne endings, respectively (Table 15.3). 

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