with stimulant and hallucinogenic
properties. It is used illegally as a
club drug.
alpha-naphthol test A biochemical test to detect the presence of carbohydrates in solution, also known
as Molisch’s test (after the Austrian
chemist H. Molisch (1856–1937), who
devised it). A small amount of alcoholic alpha-naphthol is mixed with
the test solution and concentrated
sulphuric acid is poured slowly down
the side of the test tube. A positive
reaction is indicated by the formation of a violet ring at the junction of
the liquids.
alpha particle A helium nucleus
emitted by a larger nucleus during
the course of the type of radioactive
decay known as alpha decay. As a helium nucleus consists of two protons
and two neutrons bound together as
a stable entity the loss of an alpha
particle involves a decrease in *nucleon number of 4 and decrease of 2
in the *atomic number, e.g. the
decay of a uranium–238 nucleus into
a thorium–234 nucleus. A stream of
alpha particles is known as an alpharay or alpha-radiation.
alternant Describing a conjugated
molecule in which the atoms can be
divided into two sets of alternate
atoms such that no atom has a direct
link to another atom in the same set.
Naphthalene, for example, has an alternant conjugated system.
alum See aluminium potassium
sulphate; alums.
alumina See aluminium oxide; aluminium hydroxide.
aluminate A salt formed when aluminium hydroxide or γ-alumina is
dissolved in solutions of strong bases,
such as sodium hydroxide. Aluminates exist in solutions containing
the aluminate ion, commonly written [Al(OH) 4 ]
– . In fact the ion probably is a complex hydrated ion and
can be regarded as formed from a hydrated Al
3+ ion by removal of four hydrogen ions:
[Al(H 2 O) 6 ]
3+ + 4OH
–
→ 4H 2 O +
[Al(OH) 4 (H 2 O) 2 ]
–
Other aluminates and polyaluminates, such as [Al(OH) 6 ]
3– and
23
aluminate
a
• • •
• • •
•
•
•
O O O
H H H
C C C
C C C
N N N
R
N N N
H H H
H H H
O O O
H H H
C C C
C C C
N N N
H H H
O O O
C C C
R
R
H H H
O O O
C C C
N N N
H H H
C C C
R
hydrogen bond
= amino-acid side chain
• • •
O O O
Alpha helix
www.AzShimi.ir www.AzShimi.com
properties. It is used illegally as a
club drug.
alpha-naphthol test A biochemical test to detect the presence of carbohydrates in solution, also known
as Molisch’s test (after the Austrian
chemist H. Molisch (1856–1937), who
devised it). A small amount of alcoholic alpha-naphthol is mixed with
the test solution and concentrated
sulphuric acid is poured slowly down
the side of the test tube. A positive
reaction is indicated by the formation of a violet ring at the junction of
the liquids.
alpha particle A helium nucleus
emitted by a larger nucleus during
the course of the type of radioactive
decay known as alpha decay. As a helium nucleus consists of two protons
and two neutrons bound together as
a stable entity the loss of an alpha
particle involves a decrease in *nucleon number of 4 and decrease of 2
in the *atomic number, e.g. the
decay of a uranium–238 nucleus into
a thorium–234 nucleus. A stream of
alpha particles is known as an alpharay or alpha-radiation.
alternant Describing a conjugated
molecule in which the atoms can be
divided into two sets of alternate
atoms such that no atom has a direct
link to another atom in the same set.
Naphthalene, for example, has an alternant conjugated system.
alum See aluminium potassium
sulphate; alums.
alumina See aluminium oxide; aluminium hydroxide.
aluminate A salt formed when aluminium hydroxide or γ-alumina is
dissolved in solutions of strong bases,
such as sodium hydroxide. Aluminates exist in solutions containing
the aluminate ion, commonly written [Al(OH) 4 ]
– . In fact the ion probably is a complex hydrated ion and
can be regarded as formed from a hydrated Al
3+ ion by removal of four hydrogen ions:
[Al(H 2 O) 6 ]
3+ + 4OH
–
→ 4H 2 O +
[Al(OH) 4 (H 2 O) 2 ]
–
Other aluminates and polyaluminates, such as [Al(OH) 6 ]
3– and
23
aluminate
a
• • •
• • •
•
•
•
O O O
H H H
C C C
C C C
N N N
R
N N N
H H H
H H H
O O O
H H H
C C C
C C C
N N N
H H H
O O O
C C C
R
R
H H H
O O O
C C C
N N N
H H H
C C C
R
hydrogen bond
= amino-acid side chain
• • •
O O O
Alpha helix
www.AzShimi.ir www.AzShimi.com