trophilic substitution; nucleo-
philic substitution.substrate1.The substance that is
affected by the action of a catalyst;
for example, the substance upon
which an *enzyme acts in a biochem-
ical reaction. 2.The substance on
which some other substance is ad-
sorbed or in which it is absorbed. Ex-
amples include the material to which
a dye is attached, the porous solid ab-
sorbing a gas, and the *matrix trap-
ping isolated atoms, radicals, etc.succinic acidSee butanedioic acid.
sucrose (cane sugar; beet sugar; sac-
charose) A sugar comprising one
molecule of glucose linked to a fruc-
tose molecule. It occurs widely in
plants and is particularly abundant in
sugar cane and sugar beet (15–20%),
from which it is extracted and
reÜned for table sugar. If heated to
200 °C, sucrose becomes caramel.sugar(saccharide)Any of a group of
water-soluble *carbohydrates of rela-
tively low molecular weight and typi-
cally having a sweet taste. The simple
sugars are called *monosaccharides.
More complex sugars comprise be-
tween two and ten monosaccharides
linked together: *disaccharides con-
tain two, trisaccharides three, and so
on. The name is often used to refer
speciÜcally to *sucrose (table sugar).
A- Information about IUPAC nomenclature
sugar of leadSee lead(ii)
ethanoate.
sulpha drugsSee sulphonamides.
sulphamic acidA colourless crys-
talline solid, NH 2 SO 2 OH, which is ex-
tremely soluble in water and
normally exists as the *zwitterion
H 3 N+.SO 3 –. It is a strong acid, readily
forming sulphamate salts. It is used
in electroplating, hard-water scale re-movers, herbicides, and artiÜcial
sweeteners.sulphanesCompounds of hydro-
gen and sulphur containing chains
of sulphur atoms. They have the
general formula H 2 Sn. The simplest
is hydrogen sulphide, H 2 S; other
members of the series are H 2 S 2 ,
H 2 S 3 , H 2 S 4 , etc. See sulphides.
A- Information about IUPAC nomenclature
sulphanilic acid (4-aminobenzene
sulphonic acid)A colourless crys-
talline solid, H 2 NC 6 H 4 SO 2 OH, made
by prolonged heating of phenyl-
amine (aniline) sulphate. It readily
forms diazo compounds and is used
to make dyes and sulpha drugs.
sulphateA salt or ester of sul-
phuric(VI) acid. Organic sulphates
have the formula R 2 SO 4 , where R is
an organic group. Sulphate salts con-
tain the ion SO 4 2–.sulphides1.Inorganic compounds
of sulphur with more electropositive
elements. Compounds of sulphur
with nonmetals are covalent com-
pounds, e.g. hydrogen sulphide (H 2 S).
Metals form ionic sulphides contain-
ing the S2–ion; these are salts of hy-
drogen sulphide. Polysulphidescan
also be produced containing the poly-
meric ion Sx2–. 2.(or thio ethers)Or-
ganic compounds that contain the
group –S– linked to two hydrocarbon
groups. Organic sulphides are named
from the linking groups, e.g. di-
methyl sulphide (CH 3 SCH 3 ), ethyl
methyl sulphide (C 2 H 5 SCH 3 ). They
are analogues of ethers in which the
oxygen is replaced by sulphur (hence
the alternative name) but are gener-
ally more reactive than ethers. Thus
they react with halogen compounds
to form *sulphonium compounds
and can be oxidized to *sulphoxides.sulphinate(dithionite; hyposul-substrate 508s