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Organic Chemistry Mechanisms

By Katharine Gallogly and Zach Lasry. Organic Chemistry Mechanisms. Free Radical Mechanism. Ethane + Chlorine. H. H. C. C. Cl. Cl. H. H. H. H. H. H. Cl. Cl. C. C. H. H. H. H. Chloro -Ethane + Hydrochloric acid. UV Light.

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Organic Chemistry Mechanisms

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  1. By Katharine Gallogly and Zach Lasry Organic Chemistry Mechanisms

  2. Free Radical Mechanism

  3. Ethane + Chlorine H H C C Cl Cl H H H H H H Cl Cl C C H H H H Chloro-Ethane + Hydrochloric acid

  4. UV Light • In the presence of UV Light chlorine breaks up into its free radical form Cl Cl Cl Cl

  5. The free radical is transferred from hydrogen to alkane H H Cl C C H H H H

  6. COLLISION!!!

  7. Yields

  8. Free radical alkane combines with free radical chlorine to form chloro-ethane H H C C H Cl H H H

  9. H H C C Cl COLLISION!!! H H H

  10. Free radical alkane combines with free radical chlorine to form chloro-ethane and hydrochloric acid H H Cl Cl C C H H H H

  11. Free Radical with Bromine • Bromine undergoes a reaction similar to Chlorine • Instead of a photochemical reaction (one involving UV light) the catalyst is heat • Bromine breaks apart into its free radical form 2Br • The Br bonds with one of H from the alkane forming HBr and transferring the free radical to the alkane • The alkane bonds with the other free radical Br resulting in CH3CH2Br and HBr

  12. Electrophilic Addition Mechanism

  13. Electrophiles • Alkenes have a higher density of electrons and electrophiles (electron loving compounds) are attracted • Induces an electrophilic attack

  14. Ethene+ Hydrobromide acid H H C C H Br H H H H Br C C H H H Bromo-Ethane

  15. H Br • There is a large electronegative difference between H and Br (Br is more attractive to the electrons because it has a higher electronegativity) creates a temporary dipole Br H δ+ δ- - H + Br

  16. H H - H + Br C C H H • As hydrogen bromide approaches the alkene (because H has a positive charge) electrons from the alkene shift towards the right making the left positively charged COLLISION!!! H H C C δ+ δ- H H

  17. H H Br C C H H H Bromo-Ethane

  18. H H H Br C C C H H H H H H - H + Br δ+ C C C δ- H H H H • In the case of an unsymmetrical alkane the hydrogen is attracted to the carbon which already has the most hydrogen attached to it (in this case the first one) as stated in Markovnikov’s Rule H H H Br C C C H H H H

  19. Electrophilic with Br2 • With Br2 there is no difference in electronegativity so the proximity to the high density of electrons is what creates the dipole • The bromine closer to the alkene bond is attracted to it forcing the electrons to the other bromine: H H H H H H C C C C Br Br C C H H H H H H + Br Br - Br Br

  20. Nucleophilic Mechanism

  21. Sn2Reactions • Carbonium/carbocations are positive ions which are ready for nucleophiles (lovers of positive charges) to attack • As the nucleophile approaches the delta positive it pushes electrons further away and towards the bromine • Positive bond becomes stronger and negative bond becomes weaker until the Br breaks off • They are Sn2 reactions because they involve both the halogen and the nucleophile

  22. Bromoethane + Nucleophile H H Nu - Br C C H H H H H Nu C C Br - H - H H Nucleophile Ethane + Bromine

  23. H H Nu - Br C C H H H H H - C C Br H H - Nu Br C C H H

  24. Sn1Reactions • Sn1 reactions only differ from Sn2 reactions in that they occur with only one reactant • This is made possible by the fact that secondary and tertiary alkanes are stable enough to exist as ions so they can attract the nucleophile on there own

  25. H H Nu - C C C + H COLLISION!!! C H H H H

  26. H H Nu C C C H C H H H H

  27. The End

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