《有机化学》课程教学资源（教材文献，英文版）CHAPTER 9 ALKYNES.pdf_大学文库

9.4 Structure and Bonding in Alkynes: sp Hybridization 9.3 PHYSICAL PROPERTIES OF ALKYNES Alkynes resemble alkanes and alkenes in their physical properties. They share with these Examples of physical proper- other hydrocarbons the properties of low density and low water-solubility. They are ties of alkynes are given in slightly more polar and generally have slightly higher boiling points than the corre- Appendix sponding alkanes and alkenes 9.4 STRUCTURE AND BONDING IN ALKYNES: sp HYBRIDIZATION Acetylene is linear, with a carbon-carbon bond distance of 120 pm and carbon-hydro- gen bond distances of 106 pn HC≡C-H Linear geometries characterize the H-C=C-C and C-C=C-C units of ter- minal and internal triple bonds, respectively as well. This linear geometry is responsible for the relatively small number of known cycloalkynes. Figure 9.1 shows a molecular model for cyclononyne in which the bending of the c-C=C-C unit is clearly evi- dent. Angle strain destabilizes cycloalkynes to the extent that cyclononyne is the small est one that is stable enough to be stored for long periods. The next smaller one, cyclooc tyne, has been isolated, but is relatively reactive and polymerizes on standing In spite of the fact that few cycloalkynes occur naturally, they gained recent atten- tion when it was discovered that some of them hold promise as anticancer drugs. (See the boxed essay Natural and"Designed"Enediyne Antibiotics following this section. An sp hybridization model for the carbon-carbon triple bond was develope Section 1. 18 and is reviewed for acetylene in Figure 9. 2. Figure 9.3 maps the electro- static potential in ethylene and acetylene and shows how the second T bond in acety lene causes a band of high electron density to encircle the molecule IGURE 9.1 Molecular model of cyclononyne, showing bending of bond angles th triply bonded carbons. This model represents the structure obtained when the stra is minimized according to molecular mechanics and closely matches the structure dete perimentally Notice too the degree to which the staggering of bonds on adjacent atom the overall shape of the ring Back Forward Main MenuToc Study Guide ToC Student o MHHE Website

9.3 PHYSICAL PROPERTIES OF ALKYNES Alkynes resemble alkanes and alkenes in their physical properties. They share with these other hydrocarbons the properties of low density and low water-solubility. They are slightly more polar and generally have slightly higher boiling points than the corresponding alkanes and alkenes. 9.4 STRUCTURE AND BONDING IN ALKYNES: sp HYBRIDIZATION Acetylene is linear, with a carbon–carbon bond distance of 120 pm and carbon–hydrogen bond distances of 106 pm. Linear geometries characterize the H±CPC±C and C±CPC±C units of terminal and internal triple bonds, respectively as well. This linear geometry is responsible for the relatively small number of known cycloalkynes. Figure 9.1 shows a molecular model for cyclononyne in which the bending of the C±CPC±C unit is clearly evident. Angle strain destabilizes cycloalkynes to the extent that cyclononyne is the smallest one that is stable enough to be stored for long periods. The next smaller one, cyclooctyne, has been isolated, but is relatively reactive and polymerizes on standing. In spite of the fact that few cycloalkynes occur naturally, they gained recent attention when it was discovered that some of them hold promise as anticancer drugs. (See the boxed essay Natural and “Designed” Enediyne Antibiotics following this section.) An sp hybridization model for the carbon–carbon triple bond was developed in Section 1.18 and is reviewed for acetylene in Figure 9.2. Figure 9.3 maps the electrostatic potential in ethylene and acetylene and shows how the second bond in acetylene causes a band of high electron density to encircle the molecule. H C C H 120 pm 106 pm 106 pm 180° 180° 9.4 Structure and Bonding in Alkynes: sp Hybridization 341 FIGURE 9.1 Molecular model of cyclononyne, showing bending of bond angles associated with triply bonded carbons. This model represents the structure obtained when the strain energy is minimized according to molecular mechanics and closely matches the structure determined experimentally. Notice too the degree to which the staggering of bonds on adjacent atoms governs the overall shape of the ring. Examples of physical properties of alkynes are given in Appendix 1. Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website

CHAPTER NINE Alkynes FIGURE 9.2 The carbon atoms of acetylene are connected by a o+T+ triple bond. Both carbon atoms are sp-hybridized, and each is bonded to a hydrogen by an sp-1s o bond. The component of the triple bond arises by sp-sp overlap. Each carbon has two p orbitals, the axes f which are perpendicular to each other. One t bond is formed by overlap of the p orbitals shown in(b), the other by overlap of the p orbitals shown in(c). Each t bond contains two FIGURE 9.3 Electro- static potential maps of eth ylene and acetylene. The re (red) is associated with the Tr bonds and lies be. tween the two carbons in both. This electron-rich re- plane of the molecule in eth ylene. Because acetylene ha two bonds, its band of high electron density encircles the At this point, it's useful to compare some structural features of alkanes, alkenes, and alkynes. Table 9.1 gives some of the most fundamental ones. To summarize, as we progress through the series in the order ethane - ethylene ->acetylene: 1. The geometry at carbon changes from tetrahedral trigonal planar -linear 2. The C-C and C-H bonds become shorter and stronger 3. The acidity of the C-H bonds increases. All of these trends can be accommodated by the orbital hybridization model. The bond angles are characteristic for the sp, sp", and sp hybridization states of carbon and dont require additional comment. The bond distances, bond strengths, and acidities are related to the s character in the orbitals used for bonding. s Character is a simple concept, being nothing more than the percentage of the hybrid orbital contributed by an s orbital. Thus, an sp orbital has one quarter s character and three quarters p, an sp- orbital has one third s and two thirds P, and an sp orbital one half s and one half p. We then use this information to analyze how various qualities of the hybrid orbital reflect those of its s and p contributors Take C-H bond distance and bond strength, for example. Recalling that an elec- tron in a 2s orbital is, on average, closer to the nucleus and more strongly held than an Back Forward Main MenuToc Study Guide ToC Student o MHHE Website

At this point, it’s useful to compare some structural features of alkanes, alkenes, and alkynes. Table 9.1 gives some of the most fundamental ones. To summarize, as we progress through the series in the order ethane → ethylene → acetylene: 1. The geometry at carbon changes from tetrahedral → trigonal planar → linear. 2. The C±C and C±H bonds become shorter and stronger. 3. The acidity of the C±H bonds increases. All of these trends can be accommodated by the orbital hybridization model. The bond angles are characteristic for the sp3 , sp2 , and sp hybridization states of carbon and don’t require additional comment. The bond distances, bond strengths, and acidities are related to the s character in the orbitals used for bonding. s Character is a simple concept, being nothing more than the percentage of the hybrid orbital contributed by an s orbital. Thus, an sp3 orbital has one quarter s character and three quarters p, an sp2 orbital has one third s and two thirds p, and an sp orbital one half s and one half p. We then use this information to analyze how various qualities of the hybrid orbital reflect those of its s and p contributors. Take C±H bond distance and bond strength, for example. Recalling that an electron in a 2s orbital is, on average, closer to the nucleus and more strongly held than an 342 CHAPTER NINE Alkynes (a) (b) (c) Ethylene Acetylene FIGURE 9.2 The carbon atoms of acetylene are connected by a triple bond. Both carbon atoms are sp-hybridized, and each is bonded to a hydrogen by an sp–1s bond. The component of the triple bond arises by sp–sp overlap. Each carbon has two p orbitals, the axes of which are perpendicular to each other. One bond is formed by overlap of the p orbitals shown in (b), the other by overlap of the p orbitals shown in (c). Each bond contains two electrons. FIGURE 9.3 Electrostatic potential maps of ethylene and acetylene. The region of highest negative charge (red) is associated with the bonds and lies between the two carbons in both. This electron-rich region is above and below the plane of the molecule in ethylene. Because acetylene has two bonds, its band of high electron density encircles the molecule. Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website

9.4 Structure and Bonding in Alkynes: sp Hybridization TABLE 9.1 Structural Features of Ethane, Ethylene, and Acetylene Feature Ethane Ethylene Acetylene Systematic name Ethane Ethene Ethyne Molecular formula CH CH Structural formula H-C≡c-H C-C bond distance, pm 153 134 120 C-H bond distance, pm 111 106 C bond angles 111.0° 1214° 180 C-C bond dissociation energy kJ/mol (kcal/mol) 368(88) 611(146) 820(196) C-H bond dissociation energy, kJ/mol (kcal/mol) 452(108) 536(128) Hybridization of carbon character in C-H bonds Approximate acidity as measured by Ka(pka) 10-45(45) electron in a 2p orbital, it follows that an electron in an orbital with more s character will be closer to the nucleus and more strongly held than an electron in an orbital with less s character. Thus, when an sp orbital of carbon overlaps with a hydrogen ls orbital to give a C-H o bond, the electrons are held more strongly and the bond is stronger nd shorter than electrons in a bond between hydrogen and sp-hybridized carbon. Sim- ilar reasoning holds for the shorter C-C bond distance of acetylene compared to eth ylene, although here the additional T bond in acetylene is also a factor The pattern is repeated in higher alkynes as shown when comparing propyne and propene. The bonds to the sp-hybridized carbons of propyne are shorter than the corre- ponding bonds to the sp- hybridized carbons of propene propene and propyne compare H with the experimental values? Propyne ate // An easy way to keep track of the effect of the s character of carbon is to associ- ate it with electronegativity. As the s character of carbon increases, so does that carbon's apparent electronegativity( the electrons in the bond involving that orbital are closer to arbon). The hydrogens in C-H bonds behave as if they are attached to an increasingly more electronegative carbon in the series ethane- ethylene ->acetylene PROBLEM 9.3 How do bond distances and bond strengths change with elec tronegativity in the series NH3, H2O, and HF? The property that most separates acetylene from ethane and ethylene is its acidity It, too, can be explained on the basis of the greater electronegativity of sp-hybridized carbon cor red with sp Back Forward Main MenuToc Study Guide ToC Student o MHHE Website

electron in a 2p orbital, it follows that an electron in an orbital with more s character will be closer to the nucleus and more strongly held than an electron in an orbital with less s character. Thus, when an sp orbital of carbon overlaps with a hydrogen 1s orbital to give a C±H bond, the electrons are held more strongly and the bond is stronger and shorter than electrons in a bond between hydrogen and sp2 -hybridized carbon. Similar reasoning holds for the shorter C±C bond distance of acetylene compared to ethylene, although here the additional bond in acetylene is also a factor. The pattern is repeated in higher alkynes as shown when comparing propyne and propene. The bonds to the sp-hybridized carbons of propyne are shorter than the corresponding bonds to the sp2 hybridized carbons of propene. An easy way to keep track of the effect of the s character of carbon is to associate it with electronegativity. As the s character of carbon increases, so does that carbon’s apparent electronegativity (the electrons in the bond involving that orbital are closer to carbon). The hydrogens in C±H bonds behave as if they are attached to an increasingly more electronegative carbon in the series ethane → ethylene → acetylene. PROBLEM 9.3 How do bond distances and bond strengths change with electronegativity in the series NH3, H2O, and HF? The property that most separates acetylene from ethane and ethylene is its acidity. It, too, can be explained on the basis of the greater electronegativity of sp-hybridized carbon compared with sp3 and sp2 . H 106 pm 146 pm 121 pm C C CH3 Propyne C H CH3 H H 134 pm 151 pm 108 pm C Propene 9.4 Structure and Bonding in Alkynes: sp Hybridization 343 TABLE 9.1 Structural Features of Ethane, Ethylene, and Acetylene Feature Systematic name Molecular formula C±C bond distance, pm C±H bond distance, pm H±C±C bond angles C±C bond dissociation energy, kJ/mol (kcal/mol) C±H bond dissociation energy, kJ/mol (kcal/mol) Hybridization of carbon s character in C±H bonds Approximate acidity as measured by Ka (pKa) Structural formula Ethyne C2H2 120 106 180° 820 (196) 536 (128) sp 50% 1026 (26) Acetylene H C C H Ethene C2H4 134 110 121.4° 611 (146) 452 (108) sp2 33% 1045 (45) Ethylene C H H H H C Ethane C2H6 153 111 111.0° 368 (88) 410 (98) sp3 25% 1062 (62) Ethane C H H H H H H C How do the bond distances of molecular models of propene and propyne compare with the experimental values? Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website

CHAPTER NINE Alkynes NATURAL AND"DESIGNED" ENEDIYNE ANTIBIOTICS BE eginning in the 1980s, research directed based on naturally occurring substances. Often, how- toward the isolation of new drugs derived ever, compounds that might be effective drugs are from natural sources identified a family of produced by plants and microorganisms in such small tumor-inhibitory antibiotic substances characterized amounts that their isolation from natural sources is by novel structures containing a C=C-C=C-C=c not practical. If the structure is relatively simple, chem- unit as part of a 9- or 10-membered ring With one ical synthesis provides an alternative source of the double bond and two triple bonds (-ene di -yne), these compounds soon became known as Equally important, chemical synthesis, modification, or enediyne antibiotics. The simplest member of the both can improve the effectiveness of a drug. Building class is dynemicin A*, most of the other enediynes on the enediyne core of dynemicin a, for example, have even more complicated structures. Professor Kyriacos C. Nicolaou and his associates at the Enediynes hold substantial promise as anti- Scripps Research Institute and the University of Cali- cancer drugs because of their potency and selectivity. fornia at San diego have prepared a simpler analog Not only do they inhibit cell growth, they have a that is both more potent and more selective than greater tendency to kill cancer cells than they do nor- dynemicin A. It is a"designed enediyne"in that its mal cells. The mechanism by which enediynes act in- structure was conceived on the basis of chemical rea- volves novel chemistry unique to the soning so as to carry out its biochemical task. the de C=C-C=C-C=C unit, which leads to a species signed enediyne offers the additional advantage of that cleaves dna and halts tumor growth being more amenable to large-scale synthesis The history of drug development has long been COH OH O HN OCH HOCH, CH2O Learning By Modeling contains a model of dynemicin a, which shows that the C=C ule without much angle strain. 9.5 ACIDITY OF ACETYLENE AND TERMINAL ALKYNES The C-H bonds of hydrocarbons show little tendency to ionize, and alkanes, alkenes, and alkynes are all very weak acids. The ionization constant Ka for methane, for exam- ple, is too small to be measured directly but is estimated to be about 10(pKa 60) Methane Proton Methide anion(a carbanion) Back Forward Main MenuToc Study Guide ToC Student o MHHE Website

9.5 ACIDITY OF ACETYLENE AND TERMINAL ALKYNES The C±H bonds of hydrocarbons show little tendency to ionize, and alkanes, alkenes, and alkynes are all very weak acids. The ionization constant Ka for methane, for example, is too small to be measured directly but is estimated to be about 1060 (pKa 60). H H H H C Methane H Proton H H H C Methide anion (a carbanion) 344 CHAPTER NINE Alkynes NATURAL AND “DESIGNED” ENEDIYNE ANTIBIOTICS Beginning in the 1980s, research directed toward the isolation of new drugs derived from natural sources identified a family of tumor-inhibitory antibiotic substances characterized by novel structures containing a CPC±CœC±CPC unit as part of a 9- or 10-membered ring. With one double bond and two triple bonds (-ene di- -yne), these compounds soon became known as enediyne antibiotics. The simplest member of the class is dynemicin A*; most of the other enediynes have even more complicated structures. Enediynes hold substantial promise as anticancer drugs because of their potency and selectivity. Not only do they inhibit cell growth, they have a greater tendency to kill cancer cells than they do normal cells. The mechanism by which enediynes act involves novel chemistry unique to the CPC±CœC±CPC unit, which leads to a species that cleaves DNA and halts tumor growth. The history of drug development has long been based on naturally occurring substances. Often, however, compounds that might be effective drugs are produced by plants and microorganisms in such small amounts that their isolation from natural sources is not practical. If the structure is relatively simple, chemical synthesis provides an alternative source of the drug, making it more available at a lower price. Equally important, chemical synthesis, modification, or both can improve the effectiveness of a drug. Building on the enediyne core of dynemicin A, for example, Professor Kyriacos C. Nicolaou and his associates at the Scripps Research Institute and the University of California at San Diego have prepared a simpler analog that is both more potent and more selective than dynemicin A. It is a “designed enediyne” in that its structure was conceived on the basis of chemical reasoning so as to carry out its biochemical task. The designed enediyne offers the additional advantage of being more amenable to large-scale synthesis. OH OH O O OH CH3 C C OCH3 COH O C C O HN Dynemicin A “Designed” enediyne O N S HOCH2CH2O O 2 O O C C C C O *Learning By Modeling contains a model of dynemicin A, which shows that the CPC±CœC±CPC unit can be incorporated into the molecule without much angle strain. Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website

9.5 Acidity of Acetylene and Terminal alkynes The conjugate base of a hydrocarbon is called a carbanion. It is an anion in which negative charge is borne by carbon. Since it is derived from a very weak acid,a banion such as CH3 is an exceptionally strong base In general, the ability of an atom to bear a negative charge is related to its elec- tronegativity. Both the electronegativity of an atom X and the acidity of H-X increase across a row in the periodic table. H4 NH3 H,O< Methat Ammonia Kn≈10-60 1. 8 X 10-16 Hydrogen fluoride 35×10-4 pKa≈60 (weakest acid) (strongest acid) Using the relationship from the preceding section that the effective electronega- tivity of carbon in a C-H bond increases with its s character(sp'< sp< sp), the order of hydrocarbon acidity behaves much like the preceding methane, ammonia, water, Acetylene K,≈10 a≈62 The acidity increases as carbon becomes more electronegative. lonization of acetylene gives an anion in which the unshared electron pair occupies an orbital with 50%s H-C≡C-H H++H-C=C<) Proton In the corresponding ionizations of ethylene and ethane, the unshared pair occupies an orbital with 33%(sp) and 25%(sp)s character, respectively Terminal alkynes(RC=CH) resemble acetylene in acidity (CH2CC≡CHKa=3×1026(pKa=25.5) Although acetylene and terminal alkynes are far stronger acids than other hydro- shows the greater positive char- carbons, we must remember that they are, nevertheless, very weak acids--much weaker acter of the acetylenic hydrogen than water and alcohols, for example. Hydroxide ion is too weak a base to convert acety. relative to the methyl hydrogens lene to its anion in meaningful amounts. The position of the equilibrium described by the following equation lies overwhelmingly to the left HC≡C-H Hydroxide ion Acetylide ion ( weaker acid)(weaker base (stronger base)(stronger acid Ka=1.8×10 Because acetylene is a far weaker acid than water and alcohols, these substances are not suitable solvents for reactions involving acetylide ions. Acetylide is instantly converted to acetylene by proton transfer from compounds that contain hydroxyl groups Back Forward Main MenuToc Study Guide ToC Student o MHHE Website

The conjugate base of a hydrocarbon is called a carbanion. It is an anion in which the negative charge is borne by carbon. Since it is derived from a very weak acid, a carbanion such as :CH3 is an exceptionally strong base. In general, the ability of an atom to bear a negative charge is related to its electronegativity. Both the electronegativity of an atom X and the acidity of H±X increase across a row in the periodic table. Using the relationship from the preceding section that the effective electronegativity of carbon in a C±H bond increases with its s character (sp3 sp2 sp), the order of hydrocarbon acidity behaves much like the preceding methane, ammonia, water, hydrogen fluoride series. The acidity increases as carbon becomes more electronegative. Ionization of acetylene gives an anion in which the unshared electron pair occupies an orbital with 50% s character. In the corresponding ionizations of ethylene and ethane, the unshared pair occupies an orbital with 33% (sp2 ) and 25% (sp3 ) s character, respectively. Terminal alkynes (RCPCH) resemble acetylene in acidity. Although acetylene and terminal alkynes are far stronger acids than other hydrocarbons, we must remember that they are, nevertheless, very weak acids—much weaker than water and alcohols, for example. Hydroxide ion is too weak a base to convert acetylene to its anion in meaningful amounts. The position of the equilibrium described by the following equation lies overwhelmingly to the left: Because acetylene is a far weaker acid than water and alcohols, these substances are not suitable solvents for reactions involving acetylide ions. Acetylide is instantly converted to acetylene by proton transfer from compounds that contain hydroxyl groups. Acetylene (weaker acid) Ka 1026 pKa 26 H H C C Hydroxide ion (weaker base) OH Acetylide ion (stronger base) H C C Water (stronger acid) Ka 1.8 1016 pKa 15.7 H OH (CH3)3CCPCH 3,3-Dimethyl-1-butyne Ka 3 1026 (pKa 25.5) H H C C Acetylene Proton H H C C sp Acetylide ion CH3CH3 Ethane Ka 1062 pKa 62 (weakest acid) CH2œCH2 Ethylene 1045 45 HCPCH Acetylene 1026 26 (strongest acid) CH4 Methane Ka 1060 pKa 60 (weakest acid) NH3 Ammonia 1036 36 H2O Water 1.8 1016 15.7 HF Hydrogen fluoride 3.5 104 3.2 (strongest acid) 9.5 Acidity of Acetylene and Terminal Alkynes 345 The electrostatic potential map of (CH3)3CCPCH on Learning By Modeling clearly shows the greater positive character of the acetylenic hydrogen relative to the methyl hydrogens. Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website

Amide ion is a much stronger base than acetylide ion and converts acetylene to its conjugate base quantitatively. Solutions of sodium acetylide (HCPCNa) may be prepared by adding sodium amide (NaNH2) to acetylene in liquid ammonia as the solvent. Terminal alkynes react similarly to give species of the type RCPCNa. PROBLEM 9.4 Complete each of the following equations to show the conjugate acid and the conjugate base formed by proton transfer between the indicated species. Use curved arrows to show the flow of electrons, and specify whether the position of equilibrium lies to the side of reactants or products. (a) (b) (c) (d) SAMPLE SOLUTION (a) The equation representing the acid–base reaction between propyne and methoxide ion is: Alcohols are stronger acids than acetylene, and so the position of equilibrium lies to the left. Methoxide ion is not a strong enough base to remove a proton from acetylene. Anions of acetylene and terminal alkynes are nucleophilic and react with methyl and primary alkyl halides to form carbon–carbon bonds by nucleophilic substitution. Some useful applications of this reaction will be discussed in the following section. 9.6 PREPARATION OF ALKYNES BY ALKYLATION OF ACETYLENE AND TERMINAL ALKYNES Organic synthesis makes use of two major reaction types: 1. Functional group transformations 2. Carbon–carbon bond-forming reactions Both strategies are applied to the preparation of alkynes. In this section we shall see how to prepare alkynes while building longer carbon chains. By attaching alkyl groups to acetylene, more complex alkynes can be prepared. CH3CPC±H Propyne (weaker acid) Propynide ion (stronger base) CH3CPC Methoxide ion (weaker base) OCH3 Methanol (stronger acid) H±OCH3 CH3CPCCH2OH NH2 CH2œCH2 NH2 HCPCH H2CCH3 CH3CPCH OCH3 Acetylene (stronger acid) Ka 1026 pKa 26 H H C C Amide ion (stronger base) NH2 Acetylide ion (weaker base) H C C Ammonia (weaker acid) Ka 1036 pKa 36 H NH2 346 CHAPTER NINE Alkynes Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website

Reactions that attach alkyl groups to molecular fragments are called alkylation reactions. One way in which alkynes are prepared is by alkylation of acetylene. Alkylation of acetylene involves a sequence of two separate operations. In the first one, acetylene is converted to its conjugate base by treatment with sodium amide. Next, an alkyl halide (the alkylating agent) is added to the solution of sodium acetylide. Acetylide ion acts as a nucleophile, displacing halide from carbon and forming a new carbon–carbon bond. Substitution occurs by an SN2 mechanism. The synthetic sequence is usually carried out in liquid ammonia as the solvent. Alternatively, diethyl ether or tetrahydrofuran may be used. An analogous sequence using terminal alkynes as starting materials yields alkynes of the type RCPCR. Dialkylation of acetylene can be achieved by carrying out the sequence twice. As in other nucleophilic substitution reactions, alkyl p-toluenesulfonates may be used in place of alkyl halides. PROBLEM 9.5 Outline efficient syntheses of each of the following alkynes from acetylene and any necessary organic or inorganic reagents: (a) 1-Heptyne (b) 2-Heptyne (c) 3-Heptyne SAMPLE SOLUTION (a) An examination of the structural formula of 1-heptyne reveals it to have a pentyl group attached to an acetylene unit. Alkylation of acetylene, by way of its anion, with a pentyl halide is a suitable synthetic route to 1-heptyne. 1. NaNH2, NH3 2. CH3CH2Br 1. NaNH2, NH3 2. CH3Br 2-Pentyne (81%) CH3C CCH2CH3 Acetylene HC CH 1-Butyne HC CCH2CH3 Sodium acetylide HC CNa 1-Bromobutane CH3CH2CH2CH2Br NH3 1-Hexyne (70–77%) CH3CH2CH2CH2C CH Alkyne HC CR Sodium acetylide HC CNa Alkyl halide RX Sodium halide NaX via HC C R X Acetylene HC CH Sodium acetylide HC CNa Sodium amide NaNH2 Ammonia NH3 Acetylene H H C C Monosubstituted or terminal alkyne R H C C Disubstituted derivative of acetylene R R C C 9.6 Preparation of Alkynes by Alkylation of Acetylene and Terminal Alkynes 347 NaNH2 NH3 CH3Br 4-Methyl-1-pentyne (CH3)2CHCH2C CH 5-Methyl-2-hexyne (81%) CCH3 (CH3) (CH3)2CHCH2C CNa 2CHCH2C Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website