(Chem.) A combining form (also used
adjectively), designating:
(a) (Inorganic
Chem.) The one of several acids of the same element (as the
phosphoric acids), which actually occurs with the greatest number
of hydroxyl groups; as, orthophosphoric acid. Cf.
Normal. (b) (Organic Chem.)Connection with, or affinity to, one variety of
isomerism, characteristic of the benzene compounds; -- contrasted
with meta- or para-; as, the ortho position;
hence, designating any substance showing such isomerism; as, an
ortho compound.&fist; In the graphic representation of the benzene nucleus (see
Benzene nucleus, under Benzene), provisionally adopted,
any substance exhibiting double substitution in adjacent and
contiguous carbon atoms, as 1 & 2, 3 & 4, 4 & 5, etc., is designated
by ortho-; as, orthoxylene; any substance exhibiting
substitution of two carbon atoms with one intervening, as 1 & 3, 2 &
4, 3 & 5, 4 & 6, etc., by meta-; as, resorcin or
metaxylene; any substance exhibiting substitution in opposite
parts, as 1 & 4, 2 & 5, 3 & 6, by para-; as, hydroquinone or
paraxylene.
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