Jump to:

• ortho
  ortho

  adjective

  pertaining to or occupying two adjacent positions in the benzene ring.
• ortho-
  ortho-

  a combining form occurring in loanwords from Greek, where it meant “straight,” “upright,” “right,” “correct” (orthodox ) and on this model used in the formation of compound words (orthopedic ).

ortho

¹ American  

[awr-thoh] / ˈɔr θoʊ /

adjective

Chemistry.

1. pertaining to or occupying two adjacent positions in the benzene ring.

---

ortho- ² American  

1. a combining form occurring in loanwords from Greek, where it meant “straight,” “upright,” “right,” “correct” (orthodox ) and on this model used in the formation of compound words (orthopedic ).

2. Chemistry.

   1. a combining form used in the name of that acid in a given series of acids that contains the most water (orthoboric acid ).

   2. a combining form used in the names of the salts of these acids: if the acid ends in -ic, the corresponding salt ends in -ate (orthoboric acid (H 3 BO3 ) and potassium orthoborate (K 3 BO3 )); if the acid ends in -ous, the corresponding salt ends in -ite (orthoantimonous acid (H 3 SbO3 ) and potassium orthoantimonite (K 3 SbO3 )).

---

ortho- British  

combining form

1. straight or upright

   orthotropous

2. perpendicular or at right angles

   orthoclastic

3. correct or right

   orthodontics

   orthodox

   orthography

   orthoptics

4.  o-.  (often in italics) denoting an organic compound containing a benzene ring with substituents attached to adjacent carbon atoms (the 1,2- positions) Compare oarsman Compare oarsman

   orthodinitrobenzene

5. denoting an oxyacid regarded as the highest hydrated form of the anhydride or a salt of such an acid See meta-

   orthophosphoric acid

6. denoting a diatomic substance in which the spins of the two atoms are parallel See para- 1

   orthohydrogen

---

Etymology

Origin of ortho¹

First recorded in 1875–80; independent use of ortho-

Origin of ortho-²

< Greek, combining form of orthós straight, upright, correct

Example Sentences

Under normal conditions, ortho- and para-H2 are present in a 3:1 ratio, with ortho-H2 slightly more energetically unstable than para-H2.

From Science Daily • Mar. 5, 2024

By the action of dilute nitric acid, ortho- and para-nitrophenols are obtained, the ortho-compound being separated from the para-compound by distillation in a current of steam.

From Encyclopaedia Britannica, 11th Edition, Volume 5, Slice 3 "Capefigue" to "Carneades" by Various

Concentrated acids convert them into the isomeric nitro-amines, the -NO2 group going into the nucleus in the ortho- or para- position to the amine nitrogen; this appears to indicate that the compounds are nitramines.

From Encyclopaedia Britannica, 11th Edition, Volume 8, Slice 4 "Diameter" to "Dinarchus" by Various

Mr. Tal- mage, true to the fawning, cringing spirit of ortho- doxy, lauds the living queen and cruelly maligns the genius dead.

From The Works of Robert G. Ingersoll, Vol. 5 (of 12) Dresden Edition?Discussions by Ingersoll, Robert Green

Starting with a mono-derivative, we have seen that a substituent group may enter in either of three positions to form an ortho-, meta-, or para-compound.

From Encyclopaedia Britannica, 11th Edition, Volume 6, Slice 1 "Châtelet" to "Chicago" by Various