Ortho- \Or"tho-\ ([^o]r"th[-o]-) pref. [Gr. 'orqo`s straight;
akin to Skr. [=u]rdhva upright, v[.r]dh to grow, to cause to
grow.]
[1913 Webster]
1. A combining form signifying straight, right, upright,
correct, regular; as, orthodromy, orthodiagonal, orthodox,
orthographic.
[1913 Webster]
2. (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.
[1913 Webster]
Note: 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. [1913 Webster]
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