usually has a lower energy than a
*singlet state because of the effect of
correlations of spin on the Coulomb
interactions between electrons (as in
*Hund’s rules). This can lead to substantial energy differences between
triplet and singlet states.
trisilane See silane.
trisodium phosphate(V) (sodium
orthophosphate) A colourless crystalline compound, Na 3 PO 4 , soluble in
water and insoluble in ethanol. It is
known both as the decahydrate (octagonal; r.d. 2.54) and the dodecahydrate (trigonal; r.d. 1.62) The
dodecahydrate loses water at about
76°C and the decahydrate melts at
100°C. Trisodium phosphate may be
prepared by boiling sodium carbonate with the stoichiometric amount
of phosphoric acid and subsequently
adding sodium hydroxide to the disodium salt thus formed. It is useful as
an additive for high-pressure boiler
feed water (for removal of calcium
and magnesium as phosphates), in
emulsiÜers, as a water-softening
agent, and as a component in detergents and cleaning agents. Sodium
phosphate labelled with the radioactive isotope
32 P is used in the study
of the role of phosphate in biological
processes and is also used (intravenously) in the treatment of polycythaemia.
tritiated compound See
labelling.
tritium Symbol T. An isotope of hydrogen with mass number 3; i.e. the
nucleus contains 2 neutrons and 1
proton. It is radioactive (half-life 12.3
years), undergoing beta decay to
helium–3. Tritium is used in *labelling.
triton A nucleus of a tritium atom,
consisting of a proton and two neutrons bound together; the ion T
+
formed by ionization of a tritium
atom. See also hydron.
trivalent (tervalent) Having a valency of three.
trona A mineral form of sodium
sesquicarbonate, consisting of a
mixed hydrated sodium carbonate
and sodium hydrogencarbonate,
Na 2 CO 3 .NaHCO 3 .2H 2 O.
tropylium ion The positive ion
C 7 H 7
+ , having a ring of seven carbon
atoms. The ion is symmetrical and
has characteristic properties of *aromatic compounds.
trypsin An enzyme that digests proteins (see protease). It is secreted in
an inactive form (trypsinogen) by the
pancreas into the duodenum. There,
trypsinogen is acted on by an enzyme (enterokinase) produced in the
duodenum to yield trypsin. The active enzyme plays an important role
in the digestion of proteins in the anterior portion of the small intestine.
It also activates other proteases in
the pancreatic juice.
trypsinogen See trypsin.
tryptamine A naturally occurring
alkaloid, C 10 H 12 N 2 , having an indole
ring system with a –CH 2 –CH 2 –NH 2
side chain in the 3-position of the
nitrogen-containing ring. Derivatives of tryptamines have hallucinogenic effects. An example in *psilocybin.
tryptophan See amino acid.
tub See ring conformations.
tuneable laser See dye laser.
tungsten Symbol W. A white or
grey metallic *transition element
(formerly called wolfram); a.n. 74;
r.a.m. 183.85; r.d. 19.3; m.p. 3410°C;
b.p. 5660°C. It is found in a number
of ores, including the oxides wolframite, (Fe,Mn)WO 4 , and scheelite,
537
tungsten
t
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*singlet state because of the effect of
correlations of spin on the Coulomb
interactions between electrons (as in
*Hund’s rules). This can lead to substantial energy differences between
triplet and singlet states.
trisilane See silane.
trisodium phosphate(V) (sodium
orthophosphate) A colourless crystalline compound, Na 3 PO 4 , soluble in
water and insoluble in ethanol. It is
known both as the decahydrate (octagonal; r.d. 2.54) and the dodecahydrate (trigonal; r.d. 1.62) The
dodecahydrate loses water at about
76°C and the decahydrate melts at
100°C. Trisodium phosphate may be
prepared by boiling sodium carbonate with the stoichiometric amount
of phosphoric acid and subsequently
adding sodium hydroxide to the disodium salt thus formed. It is useful as
an additive for high-pressure boiler
feed water (for removal of calcium
and magnesium as phosphates), in
emulsiÜers, as a water-softening
agent, and as a component in detergents and cleaning agents. Sodium
phosphate labelled with the radioactive isotope
32 P is used in the study
of the role of phosphate in biological
processes and is also used (intravenously) in the treatment of polycythaemia.
tritiated compound See
labelling.
tritium Symbol T. An isotope of hydrogen with mass number 3; i.e. the
nucleus contains 2 neutrons and 1
proton. It is radioactive (half-life 12.3
years), undergoing beta decay to
helium–3. Tritium is used in *labelling.
triton A nucleus of a tritium atom,
consisting of a proton and two neutrons bound together; the ion T
+
formed by ionization of a tritium
atom. See also hydron.
trivalent (tervalent) Having a valency of three.
trona A mineral form of sodium
sesquicarbonate, consisting of a
mixed hydrated sodium carbonate
and sodium hydrogencarbonate,
Na 2 CO 3 .NaHCO 3 .2H 2 O.
tropylium ion The positive ion
C 7 H 7
+ , having a ring of seven carbon
atoms. The ion is symmetrical and
has characteristic properties of *aromatic compounds.
trypsin An enzyme that digests proteins (see protease). It is secreted in
an inactive form (trypsinogen) by the
pancreas into the duodenum. There,
trypsinogen is acted on by an enzyme (enterokinase) produced in the
duodenum to yield trypsin. The active enzyme plays an important role
in the digestion of proteins in the anterior portion of the small intestine.
It also activates other proteases in
the pancreatic juice.
trypsinogen See trypsin.
tryptamine A naturally occurring
alkaloid, C 10 H 12 N 2 , having an indole
ring system with a –CH 2 –CH 2 –NH 2
side chain in the 3-position of the
nitrogen-containing ring. Derivatives of tryptamines have hallucinogenic effects. An example in *psilocybin.
tryptophan See amino acid.
tub See ring conformations.
tuneable laser See dye laser.
tungsten Symbol W. A white or
grey metallic *transition element
(formerly called wolfram); a.n. 74;
r.a.m. 183.85; r.d. 19.3; m.p. 3410°C;
b.p. 5660°C. It is found in a number
of ores, including the oxides wolframite, (Fe,Mn)WO 4 , and scheelite,
537
tungsten
t
www.AzShimi.ir www.AzShimi.com