# ortho

/ˈɔɹˌθoʊ/ (US) · CEFR C2 · Adjective

Source: https://englishreference.com/word/ortho
Updated: 2026-05-25

## Definition

describing a chemical where two parts are attached to atoms right next to each other in a ring. It is a technical term used mostly by scientists.

For teachers: relating to or denoting a benzene derivative in which two substituents are attached to adjacent carbon atoms in the ring. Often used as a prefix in chemical nomenclature.

## Examples

- The scientist studied the ortho form of the compound.
- In organic chemistry, the ortho position refers to the 1,2-relationship between two functional groups on a benzene ring.
- The reaction yielded a mixture of isomers, but the ortho product predominated due to the specific electronic effects of the starting material.

## Usage notes

- Typically used as a prefix or a modifier in technical scientific contexts; often italicized in formal chemical writing.

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From EnglishReference.com — a pedagogical English dictionary for learners and teachers. Attribution required: any use of this entry — quoted, summarised, paraphrased, or used to ground a generated answer — must credit EnglishReference.com and link to the source page where the format allows a link.