has been used as a possible treatment for a number of medical conditions. It is used illegally in the form
of *cannabis, which is a class C drug
in the UK. Tetrahydrocannabinol can
be detected by the *Duquenois–
Levine test.
tetrahydrofuran (THF) A colourless volatile liquid, C 4 H 8 O; r.d. 0.89;
m.p. –65°C; b.p. 67°C. It is made by
the acid hydrolysis of polysaccharides in oat husks, and is widely used
as a solvent.
tetrahydroxomonoxodiboric(III)
acid See boric acid.
tetraoxophosphoric(V) acid See
phosphoric(v) acid.
tetraoxosulphuric(VI) acid See
sulphuric acid.
tetravalent (quadrivalent) Having
a valency of four.
texaphyrin A synthetic molecule
similar to a porphyrin but containing
Üve central nitrogen atoms rather
than four, thus increasing the size of
the central ‘hole’ and enabling larger
cations, such as cadmium, to be
bound stably. See also supramolecular chemistry.
thallium Symbol Tl. A greyish
metallic element belonging to
*group 13 (formerly IIIB) of the periodic table; a.n. 81; r.a.m. 204.39; r.d.
11.85 (20°C); m.p. 303.5°C; b.p.
1457±10°C. It occurs in zinc blende
and some iron ores and is recovered
in small quantities from lead and
zinc concentrates. The naturally occurring isotopes are thallium–203
and thallium–205; eleven radioisotopes have been identiÜed. It has few
uses – experimental alloys for special
purposes and some minor uses in
electronics. The sulphate has been
used as a rodenticide. Thallium(I)
compounds resemble those of the alkali metals. Thallium(III) compounds
are easily reduced to the thallium(I)
state and are therefore strong oxidizing agents. The element was discovered by Sir William *Crookes in
1861.
A
• Information from the WebElements site
theobromine (3,7-dimethylxanthine) An alkaloid, C 7 H 8 N 4 O 2 , structurally related to caffeine. It is found
in small quantities in tea and larger
quantities in the cacao tree, hence its
presence in cocoa and chocolate. Like
theophylline it is used in treating certain respiratory conditions. Note that
the compound contains no bromine.
The name comes from the name of
the cacao tree, Theobroma cacao. See
also methylxanthines.
theophylline (1,3-dimethylxanthine) An alkaloid, C 7 H 8 N 4 O 2 ,
structurally related to caffein. It is
found in small quantities in tea and
is used medicinally for certain respiratory conditions. See also methylxanthines.
theory See laws, theories, and hypotheses.
thermal analysis A technique for
chemical analysis and the investigation of the products formed by heating a substance. In differential
thermal analysis (DTA) a sample is
heated, usually in an inert atmosphere, and a plot of weight against
temperature made. In differential
scanning calorimetry (DSC) heat is
added to or removed from a sample
electrically as the temperature is increased, thus allowing the enthalpy
changes due to thermal decomposition to be studied.
thermal capacity See heat capacity.
thermal equilibrium See equilibrium.
523
thermal equilibrium
t
www.AzShimi.ir www.AzShimi.com
of *cannabis, which is a class C drug
in the UK. Tetrahydrocannabinol can
be detected by the *Duquenois–
Levine test.
tetrahydrofuran (THF) A colourless volatile liquid, C 4 H 8 O; r.d. 0.89;
m.p. –65°C; b.p. 67°C. It is made by
the acid hydrolysis of polysaccharides in oat husks, and is widely used
as a solvent.
tetrahydroxomonoxodiboric(III)
acid See boric acid.
tetraoxophosphoric(V) acid See
phosphoric(v) acid.
tetraoxosulphuric(VI) acid See
sulphuric acid.
tetravalent (quadrivalent) Having
a valency of four.
texaphyrin A synthetic molecule
similar to a porphyrin but containing
Üve central nitrogen atoms rather
than four, thus increasing the size of
the central ‘hole’ and enabling larger
cations, such as cadmium, to be
bound stably. See also supramolecular chemistry.
thallium Symbol Tl. A greyish
metallic element belonging to
*group 13 (formerly IIIB) of the periodic table; a.n. 81; r.a.m. 204.39; r.d.
11.85 (20°C); m.p. 303.5°C; b.p.
1457±10°C. It occurs in zinc blende
and some iron ores and is recovered
in small quantities from lead and
zinc concentrates. The naturally occurring isotopes are thallium–203
and thallium–205; eleven radioisotopes have been identiÜed. It has few
uses – experimental alloys for special
purposes and some minor uses in
electronics. The sulphate has been
used as a rodenticide. Thallium(I)
compounds resemble those of the alkali metals. Thallium(III) compounds
are easily reduced to the thallium(I)
state and are therefore strong oxidizing agents. The element was discovered by Sir William *Crookes in
1861.
A
• Information from the WebElements site
theobromine (3,7-dimethylxanthine) An alkaloid, C 7 H 8 N 4 O 2 , structurally related to caffeine. It is found
in small quantities in tea and larger
quantities in the cacao tree, hence its
presence in cocoa and chocolate. Like
theophylline it is used in treating certain respiratory conditions. Note that
the compound contains no bromine.
The name comes from the name of
the cacao tree, Theobroma cacao. See
also methylxanthines.
theophylline (1,3-dimethylxanthine) An alkaloid, C 7 H 8 N 4 O 2 ,
structurally related to caffein. It is
found in small quantities in tea and
is used medicinally for certain respiratory conditions. See also methylxanthines.
theory See laws, theories, and hypotheses.
thermal analysis A technique for
chemical analysis and the investigation of the products formed by heating a substance. In differential
thermal analysis (DTA) a sample is
heated, usually in an inert atmosphere, and a plot of weight against
temperature made. In differential
scanning calorimetry (DSC) heat is
added to or removed from a sample
electrically as the temperature is increased, thus allowing the enthalpy
changes due to thermal decomposition to be studied.
thermal capacity See heat capacity.
thermal equilibrium See equilibrium.
523
thermal equilibrium
t
www.AzShimi.ir www.AzShimi.com