1 / 95

Chemical Change

Chemical Change. Chapter 2. types of chemical reaction. The Jablonski Diagram

ataret
Télécharger la présentation

Chemical Change

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Chemical Change Chapter 2 Dr. Suzan A. Khayyat

  2. types of chemical reaction Dr. Suzan A. Khayyat

  3. The Jablonski Diagram • The energy gained by a molecule when it absorbs a photon causes an electron to be promoted to a higher electronic energy level. Figure 3 illustrates the principal photophysicalradiative and non-radiative processes displayed by organic molecules in solution. The symbols So, S1, T2, etc., refer to the ground electronic state (So), first excited singlet state (S1), second excited triplet state (T2), and so on. The horizontal lines represent the vibrational levels of each electronic state. Straight arrows indicate radiative transitions, and curly arrows indicate non-radiative transitions. The boxes detail the electronic spins in each orbital, with electrons shown as up and down arrows, to distinguish their spin. • Note that all transitions from one electronic state to another originate from the lowest vibrational level of the initial electronic state. For example, fluorescence occurs only from S1, because the higher singlet states (S2, etc.) decay so rapidly by internal conversion that fluorescence from these states cannot compete. Dr. Suzan A. Khayyat

  4. Jablonski energy diagram Jablonski energy diagram Dr. Suzan A. Khayyat

  5. Jablonski diagram • Figure 3. The basic concepts of this Jablonski diagram are presented in the Basic Photophysics module. This version emphasizes the spins of electrons in each of the singlet states (paired, i.e., opposite orientation, spins) compared to the triplet states (unpaired, i.e., same orientation, spins). Dr. Suzan A. Khayyat

  6. Photochemical reactions with singlet Oxygen

  7. Photooxygenation Reaction Dr. Suzan A. Khayyat

  8. (1O2) Dr. Suzan A. Khayyat

  9. Dr. Suzan A. Khayyat

  10. Criteria of an ideal sensitizer • It must be excited by the irradiation to be used, small singlet triplet splitting. High ISC yield. • It must be present in sufficient concentration to absorb more strongly than the other reactants under the condition. • It must be able to transfer energy to the desired reactant, low chemical reactivity in Triplet state.

  11. Types of singlet oxygen reactions Dr. Suzan A. Khayyat

  12. 1- Ene Reaction Cis cyclic mechanism for the reaction of 1O2 with mono-olefins. Dr. Suzan A. Khayyat

  13. Dr. Suzan A. Khayyat

  14. Dr. Suzan A. Khayyat

  15. Dr. Suzan A. Khayyat

  16. Dr. Suzan A. Khayyat

  17. Dr. Suzan A. Khayyat

  18. 2-Cycloaddition Reaction (Diels Alder) Dr. Suzan A. Khayyat

  19. Direct addition reaction to produce(1,2-dioxetane) Dr. Suzan A. Khayyat

  20. Dr. Suzan A. Khayyat

  21. Dr. Suzan A. Khayyat

  22. Dr. Suzan A. Khayyat

  23. Photosensitized oxidation C2H5O-CH=CH-OC2H5 Dr. Suzan A. Khayyat

  24. Photodissociation: processes and examples • Hydrocarbons: Dr. Suzan A. Khayyat

  25. Carbonyl Compounds 1- Keetones: • Norrish Type I: The Norrish type I reaction is the photochemical cleavage or homolysis of aldehydes and ketones into two free radical intermediates. The carbonyl group accepts a photon and is excited to a photochemical singlet state. Through intersystem crossing the triplet state can be obtained. On cleavage of the α-carbon carbon bond from either state, two radical fragments are obtained. Dr. Suzan A. Khayyat

  26. Norish Type I Processes of Ketones Basic Concepts

  27. Dr. Suzan A. Khayyat

  28. Dr. Suzan A. Khayyat

  29. Norrish type II • A Norrish type II reaction is the photochemical intramolecular abstraction of a γ-hydrogen (which is a hydrogen atom three carbon positions removed from the carbonyl group) by the excited carbonyl compound to produce a 1,4-biradical as a primary photoproduct Dr. Suzan A. Khayyat

  30. Norish type II photoelimination of ketones: Cleavage of 1,4-biradicals formed by γ-hydrogen abstraction

  31. Dr. Suzan A. Khayyat

  32. Dr. Suzan A. Khayyat

  33. Dr. Suzan A. Khayyat

  34. Complete the next equations Dr. Suzan A. Khayyat

  35. Dr. Suzan A. Khayyat

  36. 2- Esters: Dr. Suzan A. Khayyat

  37. Photocycloaddition 2+2 Intermolecular cycloaddition Dr. Suzan A. Khayyat

  38. Dr. Suzan A. Khayyat

  39. Dr. Suzan A. Khayyat

  40. 2+2 Intramolecularcycloaddition Dr. Suzan A. Khayyat

  41. 2+4 Cycloaddition Dr. Suzan A. Khayyat

  42. Dr. Suzan A. Khayyat

More Related