that are generally immiscible with
water. Natural plant and animal oils
are either volatile mixtures of ter-
penes and simple esters (e.g. essen-
tial oils) or are glycerides of fatty
acids. Mineral oils are mixtures of hy-
drocarbons (e.g. *petroleum).
oil of vitriolSee sulphuric acid.
oil of wintergreen Methyl salicy-
late (methyl 2-hydroxybenzoate,
C 8 H 8 O 3 ), a colourless aromatic liquid
ester, b.p. 223°C. It occurs in the es-
sential oils of some plants, and is
manufactured from salicylic acid. It is
easily absorbed through the skin and
used in medicine for treating muscu-
lar and sciatic pain. Because of its at-
tractive smell it is also used in
perfumes and foodÛavourings.
oil sand (tar sand; bituminous sand)
A sandstone or porous carbonate
rock that is impregnated with hydro-
carbons. The largest deposit of oil
sand occurs in Alberta, Canada (the
Athabasca tar sands); there are also
deposits in the Orinoco Basin of
Venezuela, Russia, USA, Madagascar,
Albania, Trinidad, and Romania.
oil shaleAÜne-grained carbona-
ceous sedimentary rock from which
oil can be extracted. The rock con-
tains organic matter – kerogen –
which decomposes to yield oil when
heated. Deposits of oil shale occur on
every continent, the largest known
reserves occurring in Colorado, Utah,
and Wyoming in the USA. Commer-
cial production of oil from oil shale is
generally considered to be uneco-
nomic unless the price of petroleum
rises above the recovery costs for oil
from oil shale. However, threats of
declining conventional oil resources
have resulted in considerable interest
and developments in recovery tech-
niques.
oleaginousProducing or contain-
ing oil or lipids. Oleaginous microor-
ganisms, which normally contain
20–25% oil, are of interest in biotech-
nology as alternative sources of con-
ventional oils or as possible sources
for novel oils. The majority of the
oils produced by oleaginous eukary-
otic microorganisms are similar to
plant oils. One possibility under con-
sideration is the production of oils
and fats from waste material, to be
used in animal feed.
oleateA salt or ester of *oleic acid.oleÜnesSee alkenes.
oleic acidAn unsaturated *fatty
acid with one double bond,
CH 3 (CH 2 ) 7 CH:CH(CH 2 ) 7 COOH; r.d. 0.9;
m.p. 13°C. Oleic acid is one of the
most abundant constituent fatty
acids of animal and plant fats, oc-
curring in butterfat, lard, tallow,
groundnut oil, soya-bean oil, etc.
Its systematic chemical name is cis-
octadec-9-enoic acid.oleumSee disulphuric(vi) acid.
oligonucleotideA short polymer
of *nucleotides.
oligopeptideSee peptide.oligosaccharideA carbohydrate (a
type of *sugar) whose molecules con-
tain a chain of up to 20 united mono-
saccharides. Oligosaccharides are
formed as intermediates during the
digestion of *polysaccharides, such
as cellulose and starch.
olivineAn important group of
rock-forming silicate minerals crys-
tallizing in the orthorhombic system.
Olivine conforms to the general for-
mula (Mg,Fe) 2 SiO 4 and comprises a
complete series from pure magne-
sium silicate (forsterite, Mg 2 SiO 4 ) to
pure iron silicate (fayalite, Fe 2 SiO 4 ). It
is green, brown-green, or yellow-
green in colour. A gem variety of
olivine is peridot.one-pot synthesisA method of383 one-pot synthesis
o