1. F IVE M EMBERED H ETEROCYCLES P REPARATIONS AND R EACTIONS

2. Five Membered Heterocycles: Pyrrole 1 H NMR:  Aromatic: Thus, 6  electrons Sp 2 hybridised and planar Lone pair tied up in aromatic ring Pyrrole is  -electron excessive Thus, Electrophilic Aromatic Substitution is Easy Nucleophilic Substitution is Difficult Aromatic: Thus, 6  electrons Sp 2 hybridised and planar Lone pair tied up in aromatic ring Pyrrole is  -electron excessive Thus, Electrophilic Aromatic Substitution is Easy Nucleophilic Substitution is Difficult

3. Five Membered Heterocycles The least aromatic: The O atom is too electronegative The least aromatic: The O atom is too electronegative Can give addition, as well as substitution products when reacted with E + Less reactive than pyrrole, but substitution always at 2-position More aromatic than Furan Electrophilic Substitution, not addition Least reactive Thiophene has similar reactivity to benzene

4. R ESONANCE OF F IVE M EMBERED H ETEROCYCLES

5. C OF F IVE M EMBERED H ETEROCYCLES

6. P REPARATION OF F IVE M EMBERED H ETEROCYCLES

8. Electrophilic Aromatic Substitution preferred at the 2- position

9. Normal acidic nitration causes polymerization Vilsmeier Reaction Electron-withdrawing group allows substitution at the 3-position

10. Avoid concentrated mineral acids or strong Lewis acids, e.g. AlCl 3 Electrophilic Aromatic Substitution of Thiophene

11. Some Reactions of Furan Furan is more reactive than thiophene Hydrolysis of acetal Addition product

12. Some Reactions of Furan

13. Some Reactions of Thiophen

14. Some Reactions of Pyrrole

15. than the latter substitution. Some Reactions of Furan & Thiophen

16. sextet. Some Reactions of Pyrrole, Furan & Thiophen

17. Porphyrin is an important cyclic tertrapyrrole that is the core structure of heme and chlorophyll