ORGANIC REACTIONS

1. ORGANIC REACTIONS Kinds of Reactions SN Mechanisms (polar, non-polar) Dr Seemal Jelani

2. Reactions • Organic reactions • Carbon skeleton • Functional group • Formation of alkyl groups Dr Seemal Jelani

3. NULEOPHILIC SUBSTITUTION REACTION • Theme One Nucleophile is substituted for another nucleophile • General reaction Dr Seemal Jelani

4. DEFINITION OF A NUCLEOPHILE • A species that loves a nucleus • Since nuclei are positively charged, so nucleophiles are negatively charged or bear a partial negative charge • Examples are lone pairs or a hydroxide ion. • Nucleophile is an electron rich species. Dr Seemal Jelani

5. ELECTROPHILES • An ion or molecule that is electron deficient and can accept electrons • Electrophiles are often reducing agents and Lewis acids • They are either positive ions (e.g. NO2+) or Dr Seemal Jelani

6. molecules that have a positive charge on a particular atom(e.g. SO3, which has an electron-deficient sulphur atom) • In organic reactions they tend to attack negatively charged parts of a molecule Dr Seemal Jelani

7. CLASSIFICATION OF NUCLEOPHILIC • Nucleophiles can be classified according to the kind of atom that forms a new covalent bond. 1. Oxygen Nucleophile (HO-, CH3O) 2. Nitrogen Nucleophiles (NH3, RNH2…) Dr Seemal Jelani

8. 3 Sulfur Nucleophiles (HS-, RS- …) 4 Halogen Nucleophiles (I-..) Dr Seemal Jelani

9. Reactivity of Organic Halides in Nucleophilic Substitution. Dr Seemal Jelani

10. ORGANIC HALIDES • R – Xis the general formula for organic halides. R = alkyl or aryl X= F, Cl, Br & I • Most of the organic halides are creatures of the laboratory. • Only few of them have been isolated from natural products. Dr Seemal Jelani

11. ORGANIC HALIDES – USES Organohalogen compounds are important for several reason: • Versatile reagents in organic synthesis. • Can be converted into alkenes by dehydrohalogenation. Dr Seemal Jelani

12. As solvents (CH2Cl2, CHCl3) • Insecticides, herbicides, fire retardants. • Refrigerants and Polymers. Dr Seemal Jelani

13. Solvents for NSR • Protic • Aprotic • Polar • Non-Polar Dr Seemal Jelani

14. Protic Solvent • A solvent that is a Hydrogen-bond donor • The most common protic solvents contain –OH groups • Water • Low molecular weight alcohols • Low molecular weight carboxylic acids Dr Seemal Jelani

15. Aprotic Solvent • A solvent that cannot serve as a hydrogen-bond • The most common aprotic solvents are: • Dichloromethane • Diethyl ether • Dimethyl sulfoxide (DMSO) Dr Seemal Jelani

16. NUCLEOPHILIC SUBSTITUTION • Ethyl bromide reacts with hydroxide ion to give ethanol. • OH- is the nucleophile. • Bromide ion is called leaving group. • one new bond is formed Dr Seemal Jelani

17. Nucleophilic Substitution • If the nucleophile and substrate are neutral, the product will be positively charged. • If the nucleophile is a negative ion and substrate is neutral, the product will be neutral. Dr Seemal Jelani

18. The unshared pair of electron in the nucleophile can be used to make new covalent bond. Dr Seemal Jelani

19. Nucleophilic Substitution Dr Seemal Jelani

20. Nucleophilic Substitution • In principle, these reactions may be reversible. • Because the leaving group also has an unshared pair of electron and that can be used to make a new covalent bond. Dr Seemal Jelani

21. Nucleophilic Substitution • We use various method to force the reaction to go in forward direction. 1. Stronger nucleophile compared to the leaving group. 2. large excess of one of the reagent 3. Temperature Dr Seemal Jelani

22. Nucleophilic Substitution • There are some limitations: 1. What kind of hybridized carbon it is??? 2. What kind of nucleophile it is??? Dr Seemal Jelani

23. Nucleophilic Substitution • No Nucleophilic Substitution will occur on the carbon which has double bond and triple bond in which leaving group is attached Dr Seemal Jelani