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Chapter 6
Reactions of Alkynes

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06-00CO
Title
2,2-Dichlorobutane
Caption
Space-filling model of 2,2-dichlorobutane.
Notes
2,2-Dichlorobutane is the product of the reaction of 1-butyne with two molecules of HCl.
Keywords
2,2-dichlorobutane, space-filling, 1-butyne
06-00-04UN
Title
1-Hexyne and 3-Hexyne
Caption
Space-filling models of 1-hexyne and 3-hexyne.
Notes
Giving the triple bond in an alkyne the lowest possible number takes priority over giving substituents attached to alkynes low numbers.
Keywords
1-hexyne, 3-hexyne
06-00-09
Title
Structure of Ethyne
Caption
Chemical structure and ball-and-stick model of ethyne.
Notes
Because each carbon in ethyne, also known as acetylene, is sp hybridized, the bond angles around these carbons are both 180 degrees.
Keywords
structure, ethyne, ball-and-stick, acetylene
06-01a,b
Title
Figure 6.1
Caption
Orbital structures of ethyne.
Notes
(a) Each of the two pi bonds of a triple bond is formed by side-to-side overlap of a p orbital of one carbon with a parallel p orbital of the adjacent carbon. (b) A triple bond consists of a sigma bond formed by end-on sp-sp overlap (yellow) and the two pi bonds shown in (a).
Keywords
orbital, structures, ethyne, triple, bond, figure, 6.1
06-02
Title
Figure 6.2
Caption
Free-energy profiles for addition of electrophiles to alkenes and alkynes.
Notes
Although alkynes are less stable than alkenes, they react more slowly with electrophiles. The activation energy for adding an electrophile to an alkyne is greater than that for an alkene.
Keywords
free-energy, profiles, addition, electrophiles, alkene, alkyne, figure, 6.2
06-02-029UN
Title
Borane and Disiamylborane
Caption
Ball-and-stick models of borane and disiamylborane.
Notes
Borane is favored for hydrating internal alkynes, because the alkyl groups attached to each carbon are sterically bulky enough to prevent the addition of a second B-H bond to the unsaturated reaction site. Disiamylborane is used to hydrate terminal alkynes, because the two secondary isoamyl groups attached to boron provide the steric bulk necessary to prevent the addition of the second B-H bond to the unsaturated reaction site.
Keywords
ball-and-stick, borane, disiamylborane
06-02-035UN
Title
Trans Alkenes from Alkynes
Caption
Reductions of alkynes by metallic sodium or lithium dissolved in liquid ammonia yields trans alkenes.
Notes
This reaction proceeds via the formation of a vinylic anion intermediate.
Keywords
trans, alkenes, alkynes, vinylic, anion
06-02-037UN
Title
Trans and Cis Vinylic Anions
Caption
Equilibrium between trans and cis vinylic anions.
Notes
Trans vinylic anions are more stable than cis vinylic anions. This leads to the predominance of trans products in reactions which generate vinylic anions, like metal–ammonia reductions of alkynes.
Keywords
trans, cis, vinylic, anions, equilibrium
06-02-038UN
Title
Carbon Electronegativities
Caption
Electronegativities of carbon atoms decrease as the hybridization of these carbon atoms takes on more p character.
Notes
Since sp-hybridized carbons are more electronegative than sp3-hybridized carbons, anions of sp-hybridized carbon atoms are more stable (weaker bases) than anions of sp3-hybridized carbon atoms. Therefore, sp-hybridized carbons attached to hydrogens (terminal alkynes) are stronger acids than sp3-hybridized carbons attached to hydrogens (alkanes).
Keywords
carbon, electronegativities, hybridization
06-02-039UN
Title
Eletronegativity vs. Acid Strength
Caption
Atoms with the highest electronegativities yield the strongest acids when attached to hydrogen.
Notes
Hydrogens attached to more electronegative sp-hybridized carbon atoms in alkynes are more acidic than hydrogens attached to less electronegative sp2-hybridized carbons in alkenes, which are in turn more acidic than hydrogens attached to even less electronegative sp3-hybridized carbons in alkanes.
Keywords
electronegativity, acid, strength
06-02-041UN
Title
Relative Acidities
Caption
Electrostatic potential maps of various acids.
Notes
Increasing amounts of blue color on hydrogen in the stronger acids indicate more positive charge on hydrogen due to increasing electronegativities of atoms attached to hydrogen.
Keywords
relative, electrostatic, potential, maps, acidities, electronegativities
06-02-045PSS
Title
Problem-Solving Strategy Part A
Caption
Three nitrogen acids listed in order of decreasing acidity.
Notes
The strongest acid has the nitrogen with the highest electronegativity (the sp-hybridized triple-bonded nitrogen).
Keywords
06-02-046PSS
Title
Problem-Solving Strategy Part B
Caption
Three nitrogen bases listed in order of decreasing basicity.
Notes
The strongest base has the least electronegative (sp3-hybridized single-bonded) nitrogen.
Keywords

Title
Table 6.1 Boiling Points of the Smallest Hydrocarbons
Caption
Notes
Keywords

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