Presentation is loading. Please wait.

Presentation is loading. Please wait.

Five Membered Heteroaromatic Rings Their aromaticity derived from delocalization of lone pair of X so X is electron deficient so X is electron deficient.

Similar presentations


Presentation on theme: "Five Membered Heteroaromatic Rings Their aromaticity derived from delocalization of lone pair of X so X is electron deficient so X is electron deficient."— Presentation transcript:

1 Five Membered Heteroaromatic Rings Their aromaticity derived from delocalization of lone pair of X so X is electron deficient so X is electron deficient ring is electron rich ring is electron rich

2 Five Membered Heteroaromatic Rings Facts 1- aromaticity inversely proportion to electro negativity Thiophene > Pyrrole > Furan Thiophene > Pyrrole > Furan 2- Electrons not available for protonationhence not basic

3 Five Membered Heteroaromatic Rings Facts 3- 6 electrons over 5 ring atoms ….. Electron rich… so more reactive than benzene towered electrophilic substitution more reactive than benzene towered electrophilic substitution Pyrrole > Furan >Thiophene>benzene Pyrrole > Furan >Thiophene>benzene

4 Five Membered Heteroaromatic Rings Aromaticity 1- 6 electrons distributed over 5 ring atoms each 2e make coupling …. So each 2e make coupling …. So is planner, all sp 2 is planner, all sp 2

5 Five Membered Heteroaromatic Rings Aromaticity 2- Their protons show the same sort of chemical shift in NMR as the protons of benzene with δ = 6.5 ppm-8 ppm as the protons of benzene with δ = 6.5 ppm-8 ppm

6 Five Membered Heteroaromatic Rings Only for pyrrole 3-Its weak acid not basic as the secondary amines Lone pair of N is involved in cloud and not Available for sharing with acids

7 4-the patteren of reactivity 4-the patteren of reactivity The pattern of reactivity with Electrophilic reagents Cycloalkanes …… by addition reaction Cycloalkanes …… by addition reaction Aromatic compounds ……. By substitution Aromatic compounds ……. By substitution addition followed by proton loss addition followed by proton loss [ onium intermediate] [ onium intermediate] Ordre of reactivity Pyrrole > Furan >Thiophene>benzene

8 At what position Es take place

9 5-The order of aromaticity Thiophene > Pyrrole > Furan Thiophene > Pyrrole > Furan Why? In case of Thiophene [S] donate & accept electrons…… so [S] donate & accept electrons…… so delocalization as complete as benzene delocalization as complete as benzene In case of Furan [O] electronegativity more …. Diene-like character [O] electronegativity more …. Diene-like character CH 2 =CH-CH=CH 2 CH 2 =CH-CH=CH 2

10 Five Membered Heteroaromatic Rings 6- The pattern of reactivity with Electrophilic reagents Cycloalkanes …… by addition reaction Cycloalkanes …… by addition reaction Aromatic compounds ……. By substitution Aromatic compounds ……. By substitution addition followed by proton loss addition followed by proton loss [ onium intermediate] [ onium intermediate] Ordre of reactivity Pyrrole > Furan >Thiophene>benzene

11 Five Membered Heteroaromatic Rings Sources & Synthesis Pyrrole & T Pyrrole & Thiophene …. Coal Tar Pyrrole ring …. Prophyrin system….. Chlorophyll & Hemoglobin Furan ….. Decarbonylation of Furfuraldehyde ……. Oat hulls, corncobs or rice hulls

12 Five Membered Heteroaromatic Rings Synthesis Thiophene Pyrrole

13 Synthesis Furan

14 Pyrrole Reactions ESR Acetylation Vilsmier Rex Nitration Reduction Sulfonation

15 Rex with carbene Halogenation Pyrrole

16 Furan Nitration Sulfonation Acetylation Vilsmier Rex

17 Rex of furfural Cannizaro Rex Walf-Kishnerreduction Benzoin-condensation

18 Thiophene Nitration Sulfonation Acetylation Halogenation

19 Five Membered Heteroaromatic Rings Containing 2X, at least one nitrogen 1,3-Azoles1,2-Azoles Thiazole [ 1,3-thiazole] Oxazole [ 1,3-oxazole] Imidazole [ 1,3-diazole] Isothiazole [ 1,2-thiazole] Isoxazole [ 1,2-oxazole] Pyrazole [ 1,2-diazole]

20 Five Membered Heteroaromatic Rings Containing 2X, at least one nitrogen Aromaticity & Bascisity Strong base, due to the greater electron releasing capacity of the two nitrogen's of the two nitrogen's

21 Five Membered Heteroaromatic Rings Containing 2X, at least one nitrogen Aromaticity & Bascisity

22 Five Membered Heteroaromatic Rings Containing 2X, at least one nitrogen Importance of the ring Building blockes as Histidine and Histamine It exist in two tautomeric forms ….. As base & weak acid

23 Fused Five Membered Heteroaromatic Rings With one X Found in coal tar & orange blossoms, humane feces In amino acids as Tryptophan, alkaloid * pigments

24 Fused Five Membered Heteroaromatic Rings With one X Synthesis Fischer ndole Synthesis

25 Fused Five Membered Heteroaromatic Rings With one X Basicity of Indole Not basic because lone pair is delocalized and contributed to the Aromatic system

26 Fused Five Membered Heteroaromatic Rings With one X It undrego Electrophilic Subistitution at Position 3

27 Fused Five Membered Heteroaromatic Rings With one X Rex with carbene Vilsmier Rex

28 Fused Five Membered Heteroaromatic Rings With tow X In nature as N-ribosyl-dimethyl benzimidazole …. In Vit B12 Commercially as an parasisticide


Download ppt "Five Membered Heteroaromatic Rings Their aromaticity derived from delocalization of lone pair of X so X is electron deficient so X is electron deficient."

Similar presentations


Ads by Google