Phản ứng trong ankin

Organic Chemistry
4th Edition
Paula Yurkanis Bruice
Chapter 6

Reactions
of
Alkynes

Introduction to
Multistep Synthesis

Irene Lee
Case Western Reserve University
Cleveland, OH
©2004, Prentice Hall
Alkynes are hydrocarbons that contain a carbon–carbon
triple bond
General formula: CnH2n–2 (acyclic); CnH2n–4 (cyclic)
Nomenclature
In common nomenclature, alkynes are named as
substituted acetylenes
A substituent receives the lowest number if there is no
functional group suffix,
or if the same number for the functional group suffix is
obtained in both directions
The Structure of Alkynes
A triple bond is composed of a s bond and two p bonds
Addition Reactions of Alkynes
Sequential Addition of HCl
An alkyne is less reactive than an alkene
Relative Stabilities of Carbocations
Addition of Hydrogen Halides
In the presence of 1 mole equivalent of HBr
The secondary vinylic cation
is more stable
In the presence of excess HBr,
A secondary vinylic cation is about as stable as a primary
cation,
Many (but not all) alkyne addition reactions are
stereoselective
Addition of Halogens to Alkynes
Addition of Water
Examples of Water Addition
Hg2+ is added to increase the rate of water addition to
terminal alkynes
Hydroboration–Oxidation of Internal Alkynes
Hydroboration–Oxidation of Terminal Alkynes
Formation of Ketone versus Aldehyde
Addition of Hydrogen
Formation of Cis Alkene
Conversion of Internal Alkynes to Trans Alkenes
Reason for trans addition:
Acidity of a Hydrogen Bonded to an sp Hybridized Carbon
Electronegativities versus Acid Strengths
The stronger the acid, the weaker its conjugate base
top 252
Synthesis Using Acetylide Ions: Formation of C–C Bond
Designing a Synthesis
?
Example 1
Example 2
Example 3
Commercial Use of Ethyne