Aromatic Heterocyclic Compounds

Aromatic Five-Membered Heterocycles

Pyrrole is an extremely weak base

Pyrrole

Also aromatic, but lone pair of electrons is delocalized, so much weaker base.

=>

29 5-membered ring system

Other Heterocyclics

=>

NH

indole

Obenzofuran

S

benzothiophene

Other Heterocyclics

Aromatic Six-Membered-Ring Heterocycles

Pyridine

• Heterocyclic aromatic compound.• Nonbonding pair of electrons in sp2 orbital, so

weak base, pKb = 8.8.

=>

The pyridinium ion is a stronger acid than a typicalammonium ion

Quinoline and isoquinoline are known as benzopyridines

Some Biologically Important Heterocycles

Imidazole

Some Biologically Important Heterocycles

Basic or Nonbasic?

NNPyrimidine has two basicnitrogens.

N N H Imidazole has one basicnitrogen and one nonbasic.

N

N

N

N

H

Purine?=>

Chlorophyll a

Porphyrin

BILE PIGMENTS (bBILE PIGMENTS (bilirubin ilirubin and band biliverdin)iliverdin)

Bilirubin

H

Hem

Biliverdin

NNNN C C C OO

H3C C

CH2

H3C C H2C

CH2

COO-

C

C

CH3 C CH

CH2

H H

H

-OO

H2

H2 H3

H H H HH

B C D A

ADCB

H HHHHH

H3H2

H2

-OO

H

NNNN C C C OO

H3C C

CH2

H3C C H2C

CH2

COO-

C

C

CH3 C CH

CH2

Oxidat ion

Reduct ion

-Fe3+, -CO

Gallstones (bilirubin)Gallstones (bilirubin)

Collection of Pathological Department