O
occlusion 1. The trapping of small
pockets of liquid in a crystal during
crystallization. 2. The absorption of
a gas by a solid such that atoms or
molecules of the gas occupy interstitial positions in the solid lattice. Palladium, for example, can occlude
hydrogen.
ochre A yellow or red mineral form
of iron(III) oxide, Fe 2 O 3 , used as a pigment.
octadecanoate See stearate.
octadecanoic acid See stearic
acid.
octadecenoic acid A straightchain unsaturated fatty acid with the
formula C 17 H 33 COOH. Cis-octadec-9enoic acid (see oleic acid) has the formula CH 3 (CH 2 ) 7 CH:CH(CH 2 ) 7 COOH.
The glycerides of this acid are found
in many natural fats and oils.
octahedral See complex.
octahydrate A crystalline hydrate
that has eight moles of water per
mole of compound.
octane A straight-chain liquid
*alkane, C 8 H 18 ; r.d. 0.7; m.p.
–56.79°C; b.p. 125.66°C. It is present
in petroleum. The compound is isomeric with 2,2,4-trimethylpentane,
((CH 3 ) 3 CCH 2 CH(CH 3 ) 2 , iso-octane). See
octane number.
octane number A number that
provides a measure of the ability of a
fuel to resist knocking when it is
burnt in a spark-ignition engine. It is
the percentage by volume of isooctane (C 8 H 18 ; 2,2,4-trimethylpentane) in a blend with normal heptane
(C 7 H 16 ) that matches the knocking
behaviour of the fuel being tested in
a single cylinder four-stroke engine
of standard design. Compare cetane
number.
octanitrocubane See cubane.
octanoic acid (caprylic acid) A
colourless liquid straight-chain
saturated *carboxylic acid,
CH 3 (CH 2 ) 6 COOH; b.p. 239.3°C.
octavalent Having a valency of
eight.
octave See law of octaves.
octet A stable group of eight electrons in the outer shell of an atom
(as in an atom of a noble gas).
octogen See hmx.
octupole A set of eight point
charges that has zero net charge and
does not have either a dipole moment or a quadrupole moment. An
example of an octupole is a methane
molecule (CH 4 ). Octupole interactions
are much smaller than quadrupole
interactions and very much smaller
than dipole interactions.
ohm Symbol Ω. The derived *SI
unit of electrical resistance, being
the resistance between two points on
a conductor when a constant potential difference of one volt, applied between these points, produces a
current of one ampere in the conductor. The former international ohm
(sometimes called the ‘mercury
ohm’) was deÜned in terms of the resistance of a column of mercury. The
unit is named after Georg Ohm
(1787–1854).
oil Any of various viscous liquids
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occlusion 1. The trapping of small
pockets of liquid in a crystal during
crystallization. 2. The absorption of
a gas by a solid such that atoms or
molecules of the gas occupy interstitial positions in the solid lattice. Palladium, for example, can occlude
hydrogen.
ochre A yellow or red mineral form
of iron(III) oxide, Fe 2 O 3 , used as a pigment.
octadecanoate See stearate.
octadecanoic acid See stearic
acid.
octadecenoic acid A straightchain unsaturated fatty acid with the
formula C 17 H 33 COOH. Cis-octadec-9enoic acid (see oleic acid) has the formula CH 3 (CH 2 ) 7 CH:CH(CH 2 ) 7 COOH.
The glycerides of this acid are found
in many natural fats and oils.
octahedral See complex.
octahydrate A crystalline hydrate
that has eight moles of water per
mole of compound.
octane A straight-chain liquid
*alkane, C 8 H 18 ; r.d. 0.7; m.p.
–56.79°C; b.p. 125.66°C. It is present
in petroleum. The compound is isomeric with 2,2,4-trimethylpentane,
((CH 3 ) 3 CCH 2 CH(CH 3 ) 2 , iso-octane). See
octane number.
octane number A number that
provides a measure of the ability of a
fuel to resist knocking when it is
burnt in a spark-ignition engine. It is
the percentage by volume of isooctane (C 8 H 18 ; 2,2,4-trimethylpentane) in a blend with normal heptane
(C 7 H 16 ) that matches the knocking
behaviour of the fuel being tested in
a single cylinder four-stroke engine
of standard design. Compare cetane
number.
octanitrocubane See cubane.
octanoic acid (caprylic acid) A
colourless liquid straight-chain
saturated *carboxylic acid,
CH 3 (CH 2 ) 6 COOH; b.p. 239.3°C.
octavalent Having a valency of
eight.
octave See law of octaves.
octet A stable group of eight electrons in the outer shell of an atom
(as in an atom of a noble gas).
octogen See hmx.
octupole A set of eight point
charges that has zero net charge and
does not have either a dipole moment or a quadrupole moment. An
example of an octupole is a methane
molecule (CH 4 ). Octupole interactions
are much smaller than quadrupole
interactions and very much smaller
than dipole interactions.
ohm Symbol Ω. The derived *SI
unit of electrical resistance, being
the resistance between two points on
a conductor when a constant potential difference of one volt, applied between these points, produces a
current of one ampere in the conductor. The former international ohm
(sometimes called the ‘mercury
ohm’) was deÜned in terms of the resistance of a column of mercury. The
unit is named after Georg Ohm
(1787–1854).
oil Any of various viscous liquids
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