Organic Reactions

1. Organic Reactions

2. categories of organic reactions There are so many types of organic reactions. We’re going to focus on just a few. • Addition Reactions • Substitution Reactions • Elimination Reactions • Oxidation – Reduction Reaction

3. Bond Breaking: Polar and Non-polar

4. Bond Forming: Polar and Non-polar

5. I- Addition Reactions In alkenes and alkynes • In addition reactions, reactants are added to the carbon atoms in the double or triple bond. • The double or triple bond is easily broken, since it is highly reactive.

6. 1- Hydrogenation(addition of Hydrogen) In hydrogenation, • Hydrogen atoms add to the carbon atoms of a double bond or triple bond. • converts unsaturated molecule to saturated • alkene or alkyne + H2 → alkane • A catalyst such as Pt or Ni is used to speed up the reaction. • Unsaturated vegetable oils reduced to produce saturated fats used in margarine and cooking products

7. 2- Hydration(addition of water H2O) • an acid H+ catalyst is required. • water (HOH) adds to a double bond. • an H atom bonds to one C in the double bond. • an OH bonds to the other C. HOH H+ │ │ CH3─CH=CH─CH3 + H─OHCH3─CH─CH─CH3

8. Hydration When hydration occurs with a double bond that has an unequal number of H atoms, • the H atom bonds to the C in the double bond with the more H. • the OH bonds to the C in the double bond with the fewer H atoms. OHH H+ │ │ CH3─CH=CH2 + H─OHCH3─CH─CH2

9. 3- Halogenation In Halogenation, • halogen atoms add to the carbon atoms of double bond or triple bond. • Addition of Br2 and Cl2 to alkenes to yield 1,2-dihalides

10. A colour test for c=c Bond

11. Halogenation

12. 4-Hydrohalogenation In hydrohalogenation, • the atoms of a hydrogen halide add to the carbon atoms of a double bond or triple bond.

13. Markovnikov’sRule In the addition of HX, H2O, or ROH to an alkene, H adds to the carbon of the double bond having the greater number of hydrogens.

15. II- Substitution Reactions • Are characteristic reaction of saturated compounds such as alkanes. • In a substitution reaction, one atom, ion or group is replaced (substituted) by another CH4 + Cl2 CH3Cl + HCl CH3Cl + Cl2 CH2Cl2 + HCl CH2Cl2 + Cl2 CHCl3 + HCl CHCl3+ Cl2 CCl4 + HCl

16. Needs ultraviolet light to initiate the reaction.

17. NucleophilicSubstitution Reactions • Each step involves the substitution of one nucleophile (chloride ion, Cl-, or hydroxide ion, HO-) by another • Nucleophile: a molecule or ion that donates a pair of electrons to another molecule or ion to form a new covalent bond • To be a good leaving group the substituent must be able to leave as a relatively stable, weakly basic molecule or ion • In alkyl halides the leaving group is the halogen substituent-it leaves as a halide ion • Because halide ions are relatively stable and very weak bases, they are good leaving groups • Substitution of alkyl halides with nuclophiles can occur by an SN2 or SN1 path, a fundamental difference between them is the timing of bond breaking and bond forming steps

18. The SN2Reaction SN2 reaction • Substitution,Nucleophilic,Bimolecular. • Essential features of the SN2Reaction • Takes place in a single step without intermediates • Incoming nucleophile reacts with the alkyl halide or (the substrate) from a direction opposite the group that is displaced (the leaving group)

19. The SN2Reaction The mechanism of the SN2reaction when (S)-2-bromobutane reacts with –OH to give (R)-butan-2-ol • The reaction takes place in a single step • Incoming nucleophile approaches from a direction 180º away from the leaving halide ion, thereby inverting the stereochemistry at carbon

20. Substitution, Nucleophilic, Bimolecular – SN2

22. Carbocations • Carbocation:a species in which a carbon atom has only six electrons in its valence shell and bears positive charge • Carbocations are • classified as 1°, 2°, or 3° depending on the number of carbons bonded to the carbon bearing the positive charge. • electrophiles; that is, they are electron-loving. • Lewis acids. • Order of stability: 3° › 2° › 1°› methyl.

23. The SN1 Reaction Unimolecular nucleophilic substitution reaction • Mechanism of the SN1 reaction of 2-bromo-2-methylpropane with H2O involves three steps • The first step – spontaneous, unimolecular dissociation of the alkyl bromide to yield a carbocation – is rate-limiting

24. SN1 mechanism 1st step is rate determining

26. III- Elimination Reactions • Elimination: removal of atoms or group of atoms from adjacent carbon to form a carbon-carbon double bond • These are the opposite of additions • This used to prepare alkenes • An important elimination reaction is Dehydrohalogenation

27. Dehydrohalogenation (-HX)

28. Combustion A reaction in which a compound (often carbon) reacts with oxygen C + O2 CO2 CH4 + 2O2 CO2 + 2H2O C3H8 + 5O2 3CO2 + 4H2O C6H12O6 + 6O2 6CO2 + 6H2O

29. IV- Oxidation/Reduction • Oxidation:the loss of electrons • alternatively, the loss of H, the gain of O, or both • Reduction:the gain of electrons • alternatively, the gain of H, the loss of O, or both

30. Oxidation and Reduction3 hydrocarbon oxidation levels

31. Oxidation -Reduction

32. Oxidation of Alcohols • Oxidation of Primary Alcohols to Aldehydes • A primary alcohol can be oxidized to an aldehyde or a carboxylic acid • The oxidation is difficult to stop at the aldehyde stage and usually proceeds to the carboxylic acid

33. Oxidation of Secondary Alcohols to Ketones • Oxidation of a secondary alcohol stops at the ketone

34. Oxidation-ReductionReactions involve electron transfers • Oxidation of biomolecules often occurs as dehydrogenation, electron acceptor – which are usually coenzymes – are needed for such reactions to occur.

35. Practice Exercises: Classify the following rxns as substitution, elimination, or addition.

36. إن الله وملائكتــه يصلــون على النبي يــأيــها الذيـن آمنوا صلــوا عليه وسلمـــوا تسليمـــا