1 / 30

Halogenoalkanes or alkyl halides

Halogenoalkanes or alkyl halides. Sites:. http://brakkeibchem.wikispaces.com/file/view/T10D08+-+10.28.11+-+10.5-6+Halogenalkanes+Sn1+Sn2.pdf Animation: http://www.rod.beavon.clara.net/SN2.htm. Halogenoalkanes contain F, Cl, Br, I bonded to an alkyl group.

yardley-kim
Download Presentation

Halogenoalkanes or alkyl halides

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. Halogenoalkanesor alkyl halides

  2. Sites: • http://brakkeibchem.wikispaces.com/file/view/T10D08+-+10.28.11+-+10.5-6+Halogenalkanes+Sn1+Sn2.pdf • Animation: • http://www.rod.beavon.clara.net/SN2.htm

  3. Halogenoalkanes contain F, Cl, Br, I bonded to an alkyl group. CH3CH2F CH3CH2Cl CH3CH2Br CH3CH2I Bond C-F C-Cl C-Br C-I Bond Enthalpy 484 338 276 238 (kJmol-1 )

  4. Primary,Secondary,TertiaryHalogenoalkanes Primary halogenoalkanes: In a primary halogenoalkane, the carbon which carries the halogen atom is only attached to one other alkyl group.

  5. Secondary: Tertiary:

  6. HALOGENOALKANES UNDERGO SUBSTITUTION. • NUCLEOPHILIC SUBSTITUTION

  7. Nucleophile • A nucleophile is a species (an ion or a molecule) which is strongly attracted to a region of positive charge in something else. • Nucleophiles are either fully negative ions, or have a lone pair of electrons. Common nucleophiles are hydroxide ions, cyanide ions, water and ammonia.

  8. SUBSTITUTION NUCLEOPHILIC BIMOLECULAR – sn2 Primary halogenoalkanes undergo SN2: Because the mechanism of the reaction involves 2 species, it is known as an SN2 reaction. http://iverson.cm.utexas.edu/courses/310N/ReactMoviesFl05%20/SN2text.html

  9. Page 226

  10. hydroxide ion with bromoethane - H H - + HO HO Br H C C CH3 H CH3 H - Br Br C CH3 - H OH SN2 Mechanism ethanol SN2 reaction equation S(substitution) 2(species reacting in the slowest step) N(nucleophilic)

  11. SN1 – Substitution NucleophilicUnimolecular • (CH3)3CBr + OH- => (CH3)3COH + Br- • 2 bromo 2 methylpropane reacts with warm dilute aqueous sodium hydroxide solution to form the tertiary alcohol. • The rate of reaction shows that the rate depends only on the concentration of the halogenoalkane and does not depend on the concentration of OH-

  12. General rule • Primary and secondary halogenoalkanes tend to undergo SN2 reactions • Tertiary halogenoalkanes tend to undergo SN1 reactions SN2 reactivity rates follow the trend:   CH3X > primary > secondary > tertiary Why???? PAGE 227

  13. StabilityofCations

  14. Alkyl groups tend to push the bonding pair of electrons towards the carbon they are bonded to. • This is known as the positive inductive effect. • The positive charge can be spread over more atoms, increasing the stability of the ion. It will more likely be formed.

  15. SN1 x SN2

  16. Diagram of common organic reactions • . 21

  17. Answers

  18. Nucleophilic substitution cyanide ion with iodoethane CH3CH2I (ethanol) + CN-(aq) CH3CH2CN + I- propanenitrile cyanide ion with 2-bromo,2-methylpropane mechanism (CH3)3CBr (ethanol) + CN- (aqueous) (CH3)3CCN + Br- 2,2-dimethylpropanenitrile

  19. CN- ion with 2-bromo,2-methylpropane (SN1) CH3 CH3 CH3 - + CN + C C CH3 Br C CH3 CH3 CH3 CH3 CH3 - - Br Br - CN Nucleophilic substitution mechanism SN1 2,2-dimethylpropanenitrile S(substitution) 1(species reactingin the slowest step) N(nucleophilic) reaction equation

  20. Elimination

  21. Principles of elimination • Elimination of a hydrogen halide produces an alkene • In general, in aqueous solution substitution takes place • In ethanolic solution, elimination takes place

  22. Mechanisms • E1 • E2 • The particular mechanism depends on the strength of the base and the environment of the halide atom

  23. E2

  24. E1

More Related