age. For example, the abundance of
uranium-235 in natural uranium is
0.71%. This is the natural abundance,
i.e. the abundance as found in nature
before any enrichment has taken
place.
ac Anticlinal. See torsion angle.
acac The symbol for the *acetylacetonato ligand, used in formulae.
accelerant A Ûammable material
used to start and spread a Üre in
cases of arson. Petrol and parafÜn are
the substances commonly used.
Traces of accelerant are detectable by
gas chromatography in forensic
work.
accelerator A substance that increases the rate of a chemical reaction, i.e. a catalyst.
acceptor 1. (in chemistry and biochemistry) A compound, molecule,
ion, etc., to which electrons are
donated in the formation of a coordinate bond. 2. (in physics) A substance that is added as an impurity to
a *semiconductor because of its ability to accept electrons from the valence bands, causing p-type
conduction by the mobile positive
holes left. Compare donor.
accessory pigment A *photosynthetic pigment that traps light energy and channels it to chlorophyll a,
the primary pigment, which initiates
the reactions of photosynthesis. Accessory pigments include the
carotenes and chlorophylls b, c, and
d.
accumulator (secondary cell; storage battery) A type of *voltaic cell
or battery that can be recharged by
passing a current through it from an
external d.c. supply. The charging
current, which is passed in the opposite direction to that in which the
cell supplies current, reverses the
chemical reactions in the cell. The
common types are the *lead–acid accumulator and the *nickel–iron and
nickel–cadmium accumulators. See
also sodium–sulphur cell.
acenaphthene A colourless crystalline aromatic compound, C 12 H 10 ;
m.p. 95°C; b.p. 278°C. It is an intermediate in the production of some
dyes.
acetaldehyde See ethanal.
acetaldol See aldol reaction.
acetals Organic compounds formed
by addition of alcohol molecules to
aldehyde molecules. If one molecule
of aldehyde (RCHO) reacts with one
molecule of alcohol (R
1
OH) a hemiacetal is formed (RCH(OH)OR
1
). The
rings of aldose sugars are hemiacetals. Further reaction with a second
alcohol molecule produces a full acetal (RCH(OR
1 ) 2 ). It is common to
refer to both types of compound simply as ‘acetals’. The formation of acetals is reversible; acetals can be
hydrolysed back to aldehydes in
acidic solutions. In synthetic organic
chemistry aldehyde groups are often
ac
4
a
1
2
Acenaphthene
14
4
*
1*
4
1
*
14
4
*
1*
14
4
*
14
4 1*
4 1*
CNFGJ[FG
CNEQJQN
JGOKCEGVCN
JGOKCEGVCN
CNEQJQN
CEGVCN
Acetals
www.AzShimi.ir www.AzShimi.com
uranium-235 in natural uranium is
0.71%. This is the natural abundance,
i.e. the abundance as found in nature
before any enrichment has taken
place.
ac Anticlinal. See torsion angle.
acac The symbol for the *acetylacetonato ligand, used in formulae.
accelerant A Ûammable material
used to start and spread a Üre in
cases of arson. Petrol and parafÜn are
the substances commonly used.
Traces of accelerant are detectable by
gas chromatography in forensic
work.
accelerator A substance that increases the rate of a chemical reaction, i.e. a catalyst.
acceptor 1. (in chemistry and biochemistry) A compound, molecule,
ion, etc., to which electrons are
donated in the formation of a coordinate bond. 2. (in physics) A substance that is added as an impurity to
a *semiconductor because of its ability to accept electrons from the valence bands, causing p-type
conduction by the mobile positive
holes left. Compare donor.
accessory pigment A *photosynthetic pigment that traps light energy and channels it to chlorophyll a,
the primary pigment, which initiates
the reactions of photosynthesis. Accessory pigments include the
carotenes and chlorophylls b, c, and
d.
accumulator (secondary cell; storage battery) A type of *voltaic cell
or battery that can be recharged by
passing a current through it from an
external d.c. supply. The charging
current, which is passed in the opposite direction to that in which the
cell supplies current, reverses the
chemical reactions in the cell. The
common types are the *lead–acid accumulator and the *nickel–iron and
nickel–cadmium accumulators. See
also sodium–sulphur cell.
acenaphthene A colourless crystalline aromatic compound, C 12 H 10 ;
m.p. 95°C; b.p. 278°C. It is an intermediate in the production of some
dyes.
acetaldehyde See ethanal.
acetaldol See aldol reaction.
acetals Organic compounds formed
by addition of alcohol molecules to
aldehyde molecules. If one molecule
of aldehyde (RCHO) reacts with one
molecule of alcohol (R
1
OH) a hemiacetal is formed (RCH(OH)OR
1
). The
rings of aldose sugars are hemiacetals. Further reaction with a second
alcohol molecule produces a full acetal (RCH(OR
1 ) 2 ). It is common to
refer to both types of compound simply as ‘acetals’. The formation of acetals is reversible; acetals can be
hydrolysed back to aldehydes in
acidic solutions. In synthetic organic
chemistry aldehyde groups are often
ac
4
a
1
2
Acenaphthene
14
4
*
1*
4
1
*
14
4
*
1*
14
4
*
14
4 1*
4 1*
CNFGJ[FG
CNEQJQN
JGOKCEGVCN
JGOKCEGVCN
CNEQJQN
CEGVCN
Acetals
www.AzShimi.ir www.AzShimi.com