Please explain isosteres with example in detail

Abhijeet Gaurav

Isosteres are atoms, molecules, or ions of similar size containing the same number of atoms and valence electrons. one of two or more substances (as carbon monoxide and molecular nitrogen) that exhibit similarity of some properties as a result of having the same number of total or valence electrons in the same arrangement and that consist of different atoms and not necessarily the same number of atoms. Example 1 Consider neon, the noble gas at the end of the second row of the periodic table. To the left of it, fluorine has one fewer electron. If fluorine ionizes, it gains an electron to become F-, which is an isostere of Ne. Similarly, O2- is an isostere of Ne and F-. In fact, neon is part of a group of six isosteres. These are: O2-, F-, Ne, Na+, Mg2+, Al3+ Example 2 These species are isosteric: H-, He, Li+ Example 3 Nitrogen, carbon monoxide and the cyanide ion are isosteric molecules; their electronic Lewis structures are identical: :N:::N:       :C:::O:       :C:::N: In general, isosteric molecules have the same shape. This is a consequence of their identical electron arrangements. The term isosteres is not frequently heard in chemistry; the term bioisostere is commonly used in drug development. A biologically -active compound containing an isostere is called a bioisostere . This is frequently used in drug design: the bioisostere will still be recognized and accepted by the body, but its functions there will be altered as compared to the parent molecule .