<P> As an inorganic example, cisplatin (see structure above) is an important drug used in cancer chemotherapy, whereas the trans isomer (transplatin) has no useful pharmacological activity . </P> <P> Isomerism was first noticed in 1827, when Friedrich Woehler prepared silver cyanate and discovered that, although its elemental composition was identical to silver fulminate (prepared by Justus von Liebig the previous year), its properties were quite different . This finding challenged the prevailing chemical understanding of the time, which held that chemical compounds could be different only when they had different elemental compositions . After additional discoveries of the same sort were made, such as Woehler's 1828 discovery that urea has the same atomic composition as the chemically distinct ammonium cyanate, Jöns Jacob Berzelius introduced the term isomerism in 1830 to describe the phenomenon . </P> <Table> <Tr> <Th> − C ≡ N + − O − (\ displaystyle (\ ce (^ (-) \! C (\ equiv) (\ overset (+) (N)) - O ^ (-)))) </Th> <Td> The fulminate ion consists of the atoms C, N, and O arranged with N as the middle atom that is bound to each of the other two . </Td> </Tr> <Tr> <Th> ⊖ O − C ≡ N (\ displaystyle (\ ce (^ (\ ominus) \! O-C (\ equiv) N))) </Th> <Td> In comparison, the cyanate ion consists of the atoms N, C, and O arranged with C as the middle atom that is bound to each of the other two . </Td> </Tr> </Table> <Tr> <Th> − C ≡ N + − O − (\ displaystyle (\ ce (^ (-) \! C (\ equiv) (\ overset (+) (N)) - O ^ (-)))) </Th> <Td> The fulminate ion consists of the atoms C, N, and O arranged with N as the middle atom that is bound to each of the other two . </Td> </Tr>

A group of connected cells that have a similar function