with stimulant and hallucinogenic
properties. It is used illegally as a
club drug.
alpha-naphthol test A biochemi-
cal test to detect the presence of car-
bohydrates in solution, also known
as Molisch’s test (after the Austrian
chemist H. Molisch (1856–1937), who
devised it). A small amount of alco-
holic 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 forma-
tion of a violet ring at the junction of
the liquids.
alpha particleA helium nucleus
emitted by a larger nucleus during
the course of the type of radioactive
decay known as alpha decay. As a he-
lium nucleus consists of two protons
and two neutrons bound together as
a stable entity the loss of an alpha
particle involves a decrease in nu-
cleon 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 alpha-
rayor 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 al-
ternant conjugated system.alumSee aluminium potassium
sulphate; alums.aluminaSee aluminium oxide; alu-
minium hydroxide.aluminateA salt formed when alu-
minium hydroxide or γ-alumina is
dissolved in solutions of strong bases,
such as sodium hydroxide. Alumi-
nates exist in solutions containing
the aluminate ion, commonly writ-
ten [Al(OH) 4 ]–. In fact the ion proba-
bly is a complex hydrated ion and
can be regarded as formed from a hy-
drated Al3+ion by removal of four hy-
drogen ions:
[Al(H 2 O) 6 ]3++ 4OH–→4H 2 O +
[Al(OH) 4 (H 2 O) 2 ]–
Other aluminates and polyalumi-
nates, such as [Al(OH) 6 ]3–and23 aluminate
a
• •
•
• •
•
• ••
OOO
HHH
CCCCCCNNNRNNNHHH
HHHOOOHHHCCCCCCNNNHHH
OOOCCCRRHHHOOOCCCNNNHHHCCCRhydrogen bond
= amino-acid side chain• •
•
OOOAlpha helix