Cycloaddition Reactions
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This document summarizes different types of cycloaddition reactions. It begins by defining cycloaddition reactions as those where two unsaturated molecules react to form a cyclic product through the loss of two pi bonds and gain of two sigma bonds. It then classifies cycloaddition reactions based on the number of pi electrons involved - [2+2], [4+2], and 1,3-dipolar cycloadditions. Examples of each type are provided along with diagrams to illustrate the reaction mechanisms and orbital interactions. Applications of cycloadditions in organic synthesis are also briefly mentioned.
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![CONTENTS
• Cycloaddition reaction.
• Facts of cycloaddition reaction.
• Terminology- supra-antra mode
Symmetry
• F.M.O method.
• [ 2+2 ] cycloaddition reaction.
• [4+2 ] cycloaddition reaction.
• 1,3 dipolar cycloaddition reaction.
• Application of cycloadditions.
• Reference](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
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Kinds of Pericyclic Reactions and Brief details of their kinds
Molecular Orbitals and Orbitals Symmetry
Molecular Orbitals Description
Electrocyclic Reactions
Introduction to Dienes
Introduction to Dienophiles
Photochemical conditions
Ring Closure
Modes of Ring Closure
Diels- Alder Product recognition and Reversibility of Diels Alder Reaction
Conrotatory and Disrotatory arrangements
Cycloadditions in Complete Details
Dimerization , Frontier Orbitals Description, Endo Rule, Stereochemistry, Applications Hoffman's rule and a lot more……
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Chapter 11: Reactions of Alkyl Halides: Nucleophilic Substitutions and Eliminations: 11-2 The Reaction
Book Title: Organic Chemistry
Printed By: Joetta Lloyd ([email protected])
© 2016 Cengage Learning, Cengage Learning
11-2 The Reaction
In every chemical reaction, there is a direct relationship between the rate at which the
reaction occurs and the concentrations of the reactants. When we measure this relationship,
we measure the kinetics (Referring to reaction rates. Kinetic measurements are useful for
helping to determine reaction mechanisms.) of the reaction. For example, let’s look at the
kinetics of a simple nucleophilic substitution—the reaction of with to yield
plus .
With a given temperature, solvent, and concentration of reactants, the substitution occurs at
a certain rate. If we double the concentration of , the frequency of encounters between
reaction partners doubles and we find that the reaction rate also doubles. Similarly, if we
double the concentration of , the reaction rate again doubles. We call such a
reaction, in which the rate is linearly dependent on the concentrations of two species, a
second-order reaction (A reaction whose rate-limiting step is bimolecular and whose
kinetics are therefore dependent on the concentration of two reactants.) . Mathematically,
we can express this second-order dependence of the nucleophilic substitution reaction by
setting up a rate equation. As either or changes, the rate of the reaction
changes proportionately.
where
A mechanism that accounts for both the inversion of configuration and the second-order
kinetics that are observed with nucleophilic substitution reactions was suggested in 1937 by
the British chemists E. D. Hughes and Christopher Ingold, who formulated what they called
the SN 2 reaction (A bimolecular nucleophilic substitution reaction.) —short for substitution,
nucleophilic, bimolecular. (Bimolecular means that two molecules, nucleophile and alkyl
halide, take part in the step whose kinetics are measured.)
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The essential feature of the mechanism is that it takes place in a single step, without
intermediates, when the incoming nucleophile reacts with the alkyl halide or tosylate (the
substrate) from a direction opposite the group that is displaced (the leaving group). As the
nucleophile comes in on one side of the substrate and bonds to the carbon, the halide or
tosylate departs from the other side, thereby inverting the stereochemical configuration. The
process is shown in Figure 11-3 for the reaction of (S)-2-bromobutane with to give
(R)-2-butanol.
Figure 11-3
Mechanism
The mechanism of the reaction. The reaction takes place in a single ...
Mechanism of Organic Reactions.pptx
Organic Reaction Mechanism
Chemistry XI
JEE Neet Chemistry
Its A Ppt For Wasy Understanding For the Topic For Engineering and Medical Aspirants
Pericyclic reaction lecture 1
Pericyclic reaction lecture 1Dr.Mohd Kamil Hussain, Department of Chemistry, Govt Raza PG College Rampur
Pericyclic reactions are defined as reactions that occur by concerted cyclic shift of electrons. In concerted reaction, reactant bonds are broken and product bonds are formed at the same time. Similar to Cycloaddition Reactions (20)
Reaction mechanism ppt for advance organic chemistry.pptx
Reaction mechanism ppt for advance organic chemistry.pptx
Sigmatropic_Reaction sem II kavit maheshwari_sem2.pptx
Sigmatropic_Reaction sem II kavit maheshwari_sem2.pptx
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- 1. SAMARAT PRITHVIRAJ CHAUHAN GOVERNMENT COLLAGE,AJMER 2021-22 DEPARTMENT OF CHEMISTRY CYCLOADDITION REACTIONS Submitted BY: Manisha kanwar M.Sc(Chemistry) Semester 2nd
- 2. CONTENTS • Cycloaddition reaction. • Facts of cycloaddition reaction. • Terminology- supra-antra mode Symmetry • F.M.O method. • [ 2+2 ] cycloaddition reaction. • [4+2 ] cycloaddition reaction. • 1,3 dipolar cycloaddition reaction. • Application of cycloadditions. • Reference
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- 4. THE CYCLOADDITION REACTION ARE CLASSIFIED WITH RESPECT TO THREE FACTS OF THE REACTION : (i) A cycloaddition reaction involves the formation of two bonds between the termini of two independent -systems, resulting in ring formation - or the reverse process. (ii) Cycloaddition reactions are stereospecific (e.g. cis/trans isomers). The stereospecificity being afforded by the suprafacial or antarafacial nature of the approach of the two -units in the transition state. (iii) The suprafacial or antarafacial process involved in the bond making process is controlled by the HOMO/LUMO interactions of the two -systems in the transition state.
- 5. • New bonds to the same side of the -system • New bonds to the opposite side of the - system
- 6. SYMMETRY IN LINEAR CONJUGATED PI- SYSTEM M-Symmetry(mirror-symmetry) • M-symmetry means plane of symmetry C2-Symmetry(centre-symmetry) • C2-symmetry means centre of symmetry
- 7. FMO METHOD In order for a cycloaddition to occur,must be bonding overlap between p orbital at the terminal carbons of each electron system ,this is where the new sigma-bonds are formed. Lets us explain this point with a [4+2] cycloaddition. Let us suppose that diene (4- component) behaves as electron donar and the dienophile (2- component)as the electron acceptor.
- 8. [2+2] CYCLOADDITION REACTION When 2 electron and 2 electron system combine together to give cycloalkene the reaction is called 2+2 cycloaddition it can occur suprafical antrafacial mode of addition.
- 9. [2+2] CYCLOADDITIONS THERMAL INDUCED
- 10. [2+2] CYCLOADDITIONS • PHOTO INDUCED-
- 11. [4+2] CYCLOADDITION REACTION • A cycloaddition reaction is the concerted bonding together of two independent pi-electron systems to form a new ring of atoms. ... The Diels-Alder cycloaddition is classified as a [4+2] process because the diene has four pi-electrons that shift position in the reaction and the dienophile has two.
- 12. [4+2] cycloaddition reaction • THERMAL INDUCED REACTION –There are two possible interactions, HOMO (diene) – LUMO (dienophile) and HOMO(Dienophile)-LUMO(diene). • 1.HOMO(Diene)-LUMO(dienophile)
- 14. [4+2] cycloaddition reaction • PHOTO INDUCED REACTION-When diene is excited by light.its HOMO becomes Ψ₃* which has m symmetry and this MO cannot overlap with LUMO of ethylene which has C₂ symmetry. • Thus photochemical Cycloaddition of [4+2] Systemis symmetry forbidden reaction.
- 15. 1,3 –DIPOLAR CYCLOADDITIONS • 1,3-Dipolar cycloadditions represent synthetically important reactions for the preparation of heterocyclic five-membered rings. They belong into the group of [4+2] cycloadditions according to the Woodward-Hoffmann classification. •
- 16. • INTERACTION BETWEEN HOMO OF 1,3-DIPOLE AND LUMO OF DIPOLARPHILE
- 17. APPLICATIONS OF CYCLOADDITIONS • N1 unit transfer reaction to C–C double bonds. • [3+2] Cycloaddition of α, β-unsaturated metal-carbene complexes. • Formal [3+3] cycloaddition approach to natural product synthesis. • Development of new methods for the construction of heterocycles based on cycloaddition reaction of 1,3- dipoles. • Cycloreversion approach for preparation of large π- conjugated compounds. • Transition metal-catalyzed or mediated [5+1] cycloadditions. https://www.wiley.com/en- us/Methods+and+Applications+of+Cycloaddition+Reactions+in+Organic+Syntheses-p-9781118299883
- 18. REFERENCE • Advance organic chemistry- DR. JAGDAMBA SINGH(Pragati edition). https://www.goodreads.com/work/editions/66293573-advance-organic-chemistry • Cycloaddition reaction in organic synthesis- W.Carruthers. Print ISBN:9783527301591 |Online ISBN:9783527600250 |DOI:10.1002/3527600256