Definition of isomer in English:



  • 1Chemistry
    Each of two or more compounds with the same formula but a different arrangement of atoms in the molecule and different properties.

    • ‘However, several research groups have suggested cis isomers of lycopene are better absorbed than the all-trans form.’
    • ‘Conjugated linoleic acid is a mixture of positional and geometric isomers of linoleic acid.’
    • ‘In 1907, he synthesized a pair of geometric isomers that confirmed his predictions.’
    • ‘There is evidence that tocopherol isomers differ from each other in their functional properties.’
    • ‘An aromatic molecule containing two nitro groups will have three positional isomers.’
    • ‘The plant material contains only the active isomers.’
  • 2Physics
    Each of two or more atomic nuclei that have the same atomic number and the same mass number but different energy states.

    • ‘Constitutional isomers are isomers that have different atomic connectivities.’
    • ‘One form is called the (+) isomer because it rotates polarized light to the right, in a positive direction.’
    • ‘The article proclaimed the dawn of the age of atomic aircraft powered by hafnium-178 isomer reactors.’


Mid 19th century from Greek isomerēs ‘sharing equally’, from isos ‘equal’ + meros ‘a share’.