isomer
In chemistry, an isomer refers to one of two or more compounds that have the same molecular formula but differ in the arrangement or spatial orientation of atoms. Isomers typically exhibit different chemical and physical properties, and there are several types of isomerism, each illustrating a unique aspect of molecular structure.
- Structural (Constitutional) Isomers: These isomers differ in the connectivity of their atoms. The same atoms are connected in different ways, leading to different molecular structures. An example is butane and isobutene, which both have the formula C₄H₁₀ but differ in how the carbon atoms are connected.
- Stereoisomers: These isomers have the same molecular formula and sequence of bonded atoms, but they differ in the three-dimensional orientations of their atoms in space. Stereoisomerism includes:
- Geometric Isomers (Cis-Trans Isomers): These isomers differ in their spatial arrangement around a double bond or a ring structure, where the rotation is restricted. 'Cis' refers to functional groups being on the same side, while 'trans' refers to them being on opposite sides.
- Optical Isomers (Enantiomers): These are mirror images of each other that cannot be superimposed. They have the same physical properties except for their effect on polarized light and reactions in a chiral environment.
- Conformational Isomers: These isomers differ by rotation around a single bond. They are often rapidly interconverted at room temperature, making them difficult to separate. Examples include the different conformations of ethane and butane.
Isomerism is a key concept in organic chemistry, explaining the existence of different compounds with the same molecular formula, each with its own unique set of properties. This concept is particularly important in fields like pharmaceuticals, where different isomers of a compound can have vastly different therapeutic effects.