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Chapter 4 Alkynes

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Chapter 4 Alkynes 4.1 Nomenclature 4.2 Structure of Alkynes 4.3 Reactions of alkynes 4.3.1 Acidity of Terminal Alkynes 4.3.2 Application of the Acidity of – PowerPoint PPT presentation

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Title: Chapter 4 Alkynes


1
Chapter 4 Alkynes
4.1 Nomenclature 4.2 Structure of Alkynes 4.3
Reactions of alkynes 4.3.1 Acidity of Terminal
Alkynes 4.3.2 Application of the Acidity of
Terminal Alkynes in Organic Synthesis 4.3.3
Hydrogenation of Alkynes 1. Syn-addition of
H2 Synthesis of cis-Alkyenes
2. Metal-Ammonia Reduction of Alkynes
Synthesis of trans-Alkenes
2
  • 4.3.4 Electrophilic Addition of Alkynes
  • a. Addition of HX
  • b. Hydration of Alkynes
  • c. Addition of X2
  • d. Hydroboration and Oxidation of Alkynes
  • 4.4 Oxidation of Alkynes
  • 4.5 Preparation of Unsaturated
  • Hydrocarbons
  • 4.5.1 Preparation of alkenes
  • Dehydrohalogenation of alkyl halides
  • 2. Dehydration (??)of alcohols
  • 4.5.1 Preparation of Alkynes
  • Dehydrohalogenation of vicinal alkyl
  • dihalides
  • b. Alkylation of alkynide ions

3
P134,4.13
Alkynes
Hydrocarbons containing a carbon-carbon tripl
e bond.
Terminal or mono-substituted
alkynes
Internal or disubstituted
(??)
1. Numbering starts from the end near the
first multiple bond.
4.1 Nomenclature
2. When there is a choice, double bonds receive
lower numbers than triple bonds.
1-Butyne
  • Alkenyne (??)

1-penten-4-yne (1-??-4-?)
3-Penten-1-yne (3-??-1-?)
4
4.2 Structure of Alkynes
P18, 1.10
Acetylene (ethyne)
sp Hybrid orbitals
sp-hybridized state
C
Exited state
Ground state
Hybri- dization
Promotion of electron
The shape of an sp hybrid obital
Each sp hybrid orbital
50 s character 50 p character
5
An sp-hybridized carbon atom
The two sp hybride orbitals are oriented 180away
from each other, perpendicular to the two
remaining p orbitals.
Geometric structure of sp-hybridized C atoms is
linear.
In the mole. of acetylene, the formation of
C-Csbond sp-sp overlap
The formation C-H sbonds sp-1s overlap.
6
The formation C-H sbonds sp-1s overlap.
The formation of two C-Cpbonds 2py-2py overlap
and 2pz-2pz overlap.
7
H
H
pbond
sbond
Carbon-carbon triple bonds
pbond
8
4.3 Reactions of alkynes
4.3.1 Acidity of Terminal Alkynes
Acetylene
Carbanion
Acidity
Conjugate base (???)
pKa 3.2 15.8 16-17
26 38
9
4.3.2 Application of the Acidity of Terminal
Alkynes in Organic Synthesis
1. Preparation of Metal Alkynides
P138,4.16
Acid-base reaction
2. Formation of C-C Bonds
(Synthesis of Alkynes)
Sodium alkynides are useful intermediates as
nucleophile.
10
Primary halides
Ch. P77
3. Formation of other metal alkynides
Reagent NH3 solution of AgNO3 or NH3 solution
of CuCl
Ch.P52(?)(1)
4.3.3 Hydrogenation of Alkynes
11
  • Syn-addition of H2
  • Synthesis of cis-Alkyenes

Lindlar catalyst
(96)
Lindlar catalyst Pd/ CaCO3, Pb(Ac)2-quinoline

(??)
P-2 catalyst
Ch P53
12
2. Metal-Ammonia Reduction of Alkynes
Synthesis of trans-Alkenes
4.3.4 Electrophilic Addition of Alkynes
  • Reactivity Alkynes lt Alkenes
  • Regioselectivit Follow Markov.s Rule

a. Addition of HX
13
b. Hydration of Alkynes
2-Hexanone
Keto-enol tautomerism(??-???????)
14
c. Addition of X2
d. Hydroboration and Oxidation of Alkynes
Ch P67
6.4 Oxidation of Alkynes
An internal alkynes
Identification of C-C triple bonds
15
6.5 Preparation of Unsaturated
Hydrocarbons
6.5.1 Preparation of alkenes
1. Dehydrohalogenation of alkyl halides
(????)
Bromocyclohexane Cyclohexene (81)
2. Dehydration (??)of alcohols
Elimination
16
6.5.1 Preparation of Alkynes
  • Dehydrohalogenation of vicinal alkyl
  • dihalides

Diphenylacetylene(85)
b. Alkylation of metal alkynide
17
Problems to Chapter 4. Alkyne P146. 4.25(b) 4.26
(b),(c) 4.29(c) 4.41 Show the reactions. 4.42 4.44
4.45(c) 4.48 4.52 4.56
18
  • Additional problems
  • 1.Predict the products from reaction of 2-
  • hexyne with the following reagents
  • 2 equiv Br2 (b) 1equiv HBr (c) Excess HBr
  • (d) Li in NH3 (e) H2O, H2SO4, HgSO4

2. How would you carry out the following
reaction?
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