equally be deÜned as the energy re-
quired to increase the surface area
isothermally by one square metre,
i.e. it can be measured in joules per
metre squared (which is equivalent
to N m–1).
The property of surface tension is
responsible for the formation of liq-
uid drops, soap bubbles, and menis-
cuses, as well as the rise of liquids in
a capillary tube (capillarity), the ab-
sorption of liquids by porous sub-
stances, and the ability of liquids to
wet a surface.
surfactant(surface active agent)A
substance, such as a detergent,
added to a liquid to increase its
spreading or wetting properties by
reducing its surface tension.
suspension A mixture in which
small solid or liquid particles are sus-
pended in a liquid or gas.
SYBYL line notationA type of
line notation, similar to *SMILES but
with some additional features. In
SLN, hydrogens are not omitted, so
ethane is CH3CH3. Wild-card atoms
and groups can be speciÜed for
searching.
sylvite(sylvine)A mineral form of
*potassium chloride, KCl.
symmetric topSee moment of in-
ertia.
symmetry The property of an ob-
ject that enables it to undergo cer-
tain manipulations, called symmetry
operations, such that its new state is
indistinguishable from its original
state. Examples include inversion
through a point, reÛection through a
plane, and rotation about an axis.
The geometrical feature of the object
with respect to which the symmetry
operation is carried out is termed a
symmetry element. In the above ex-
amples, a point through which inver-
sion can be performed, a plane of
reÛection, and an axis of rotation are
the symmetry elements. See also mo-
lecular symmetry.
symmetry-adapted linear com-
binationsSee salc.synSee torsion angle.synchrotron radiation Electro-
magnetic radiation produced when
charged particles travel in a curved
path. In a generator of synchrotron
radiation, electrons are accelerated in
a synchrotron and injected into a
storage ring where they circulate at a
constant energy. Radiation can be
taken from the storage ring tangen-
tially at various points around the
ring. The advantage of this type of
source is that it gives a narrow in-
tense beam that is tunable to a par-
ticular wavelength over a whole
range from infrared radiation to hard
X-rays. Synchrotron radiation is used
for a variety of studies including crys-
tallography, X-ray scattering, and ion-
ization experiments.synclinalSee torsion angle.syndiotacticSee polymer.syneresis The spontaneous separa-
tion of the solid and liquid compo-
nents of a gel on standing.synperiplanarSee torsion angle.
synthesisThe formation of chemi-
cal compounds from more simple
compounds.
synthesis gasSee haber process.syntheticDescribing a substance
that has been made artiÜcially; i.e.
one that does not come from a nat-
ural source.synthonA fragment obtained by
disconnection in *retrosynthetic
analysis. By analogy, units building
up structures by self-assembly in
*supramolecular chemistry are some-515 synthon
s