isomer

noun

iso·​mer ˈī-sə-mər 

1

: one of two or more compounds, radicals, or ions that contain the same number of atoms of the same elements but differ in structural arrangement and properties

2

: a nuclide isomeric with one or more others

Examples of isomer in a Sentence

Recent Examples on the Web

Chiral molecules come in two versions, or isomers, defined by their optical activity. — Sajish Mathew, The Conversation, 7 Oct. 2026

However, heat processing during canning altered the lutein and zeaxanthin isomers, which are structural variants considered less biologically active as antioxidants than their naturally occurring forms. — Anna Giorgi, Verywell Health, 2 July 2026

But the Dewar isomers of the pyrimidones are incredibly stable. — Jacek Krywko, ArsTechnica, 16 Feb. 2026

That is the more potent of the drug’s two isomers and can be found in both street meth and prescription medications such as Desoxyn. — Daniel Libit, Sportico.com, 21 Jan. 2026

Word History

Etymology

International Scientific Vocabulary, back-formation from isomeric

First Known Use

1855, in the meaning defined at sense 1

Phrases Containing isomer

• structural isomer

Kids Definition

isomer

noun

iso·​mer ˈī-sə-mər 

: one of two or more chemical compounds or groups that have the same numbers of atoms of the same elements but differ in structure

isomeric

ˌī-sə-ˈmer-ik

adjective

isomerism

ī-ˈsäm-ə-ˌriz-əm

noun

Medical Definition

isomer

noun

iso·​mer ˈī-sə-mər 

1

: any of two or more compounds, radicals, or ions that contain the same number of atoms of the same elements but differ in structural arrangement and properties

2

: a nuclide isomeric with one or more others