tem. For example, the sequence for
some common ligands is I, Br, Cl,
SO 3 H, OCOCH 3 , OCH 3 , OH, NO 2 , NH 2 ,
COOCH 3 , CONH 2 , COCH 3 , CHO,
CH 2 OH, C 6 H 5 , C 2 H 5 , CH 3 , H. The system was jointly developed by the
British chemists Robert Sidney Cahn
(1899–1981) and Sir Christopher Kelk
Ingold (1893–1970) and the Bosnian–
Swiss chemist Vladimir Prelog (1906–
98).
circular birefringence A phenomenon in which there is a difference
between the refractive indices of the
molecules of a substance for rightand left-circularly polarized light. Circular birefringence depends on the
way in which the electromagnetic
Üeld interacts with the molecule, and
is affected by the handedness of the
molecule, and hence its polarizability. If a molecule has the shape of a
helix, the polarizability is dependent
on whether or not the electric Üeld
of the electromagnetic Üeld rotates in
the same sense as the helix, thus giving rise to circular birefringence.
circular dichroism (CD) The production of an elliptically polarized
wave when a linearly polarized light
wave passes through a substance that
has differences in the extinction
coefÜcients for left- and right-handed
polarized light. The size of this effect
is given by φ = π/λ(η l – η r ), where φ is
the ellipticity of the beam that
emerges (in radians), λ is the wavelength of the light, and η l and η r are
the absorption indices of the left- and
right-handed circularly polarized
light, respectively. Circular dichroism is a property of optically active
molecules and is used to obtain information about proteins. See also cd
spectrum.
circular polarization See polarization of light.
cis See isomerism; torsion angle.
127
Clapeyron–Clausius equation
c
A
• Information about IUPAC nomenclature
cisplatin A platinum complex, cis[PtCl 2 (NH 3 ) 2 ], used in cancer treatment to inhibit the growth of
tumours. It acts by binding between
strands of DNA.
citrate A salt or ester of citric acid.
citric acid A white crystalline
hydroxycarboxylic acid,
HOOCCH 2 C(OH)(COOH)CH 2 COOH;
r.d. 1.54; m.p. 153°C. It is present in
citrus fruits and is an intermediate in
the *Krebs cycle in plant and animal
cells.
citric-acid cycle See krebs cycle.
CL20 See hniw.
Claisen condensation A reaction
of esters in which two molecules of
the ester react to give a keto ester,
e.g.
2CH 3 COOR → CH 3 COCH 2 COOR
+ ROH
The reaction is catalysed by sodium
ethoxide, the mechanism being similar to that of the *aldol reaction. It is
named after Ludwig Claisen
(1851–1930).
Clapeyron–Clausius equation A
differential equation that describes
the relationship between variables
when there is a change in the state
of a system. In a system that has two
*phases of the same substance, for
example solid and liquid, heat is
added or taken away very slowly so
that one phase can change reversibly
into the other while the system remains at equilibrium. If the two
phases are denoted A and B, the
Clapeyron–Clausius equation is:
dp/dT = L/T(V B –V A ),
where p is the pressure, T is the thermodynamic temperature, L is the
heat absorbed per mole in the
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some common ligands is I, Br, Cl,
SO 3 H, OCOCH 3 , OCH 3 , OH, NO 2 , NH 2 ,
COOCH 3 , CONH 2 , COCH 3 , CHO,
CH 2 OH, C 6 H 5 , C 2 H 5 , CH 3 , H. The system was jointly developed by the
British chemists Robert Sidney Cahn
(1899–1981) and Sir Christopher Kelk
Ingold (1893–1970) and the Bosnian–
Swiss chemist Vladimir Prelog (1906–
98).
circular birefringence A phenomenon in which there is a difference
between the refractive indices of the
molecules of a substance for rightand left-circularly polarized light. Circular birefringence depends on the
way in which the electromagnetic
Üeld interacts with the molecule, and
is affected by the handedness of the
molecule, and hence its polarizability. If a molecule has the shape of a
helix, the polarizability is dependent
on whether or not the electric Üeld
of the electromagnetic Üeld rotates in
the same sense as the helix, thus giving rise to circular birefringence.
circular dichroism (CD) The production of an elliptically polarized
wave when a linearly polarized light
wave passes through a substance that
has differences in the extinction
coefÜcients for left- and right-handed
polarized light. The size of this effect
is given by φ = π/λ(η l – η r ), where φ is
the ellipticity of the beam that
emerges (in radians), λ is the wavelength of the light, and η l and η r are
the absorption indices of the left- and
right-handed circularly polarized
light, respectively. Circular dichroism is a property of optically active
molecules and is used to obtain information about proteins. See also cd
spectrum.
circular polarization See polarization of light.
cis See isomerism; torsion angle.
127
Clapeyron–Clausius equation
c
A
• Information about IUPAC nomenclature
cisplatin A platinum complex, cis[PtCl 2 (NH 3 ) 2 ], used in cancer treatment to inhibit the growth of
tumours. It acts by binding between
strands of DNA.
citrate A salt or ester of citric acid.
citric acid A white crystalline
hydroxycarboxylic acid,
HOOCCH 2 C(OH)(COOH)CH 2 COOH;
r.d. 1.54; m.p. 153°C. It is present in
citrus fruits and is an intermediate in
the *Krebs cycle in plant and animal
cells.
citric-acid cycle See krebs cycle.
CL20 See hniw.
Claisen condensation A reaction
of esters in which two molecules of
the ester react to give a keto ester,
e.g.
2CH 3 COOR → CH 3 COCH 2 COOR
+ ROH
The reaction is catalysed by sodium
ethoxide, the mechanism being similar to that of the *aldol reaction. It is
named after Ludwig Claisen
(1851–1930).
Clapeyron–Clausius equation A
differential equation that describes
the relationship between variables
when there is a change in the state
of a system. In a system that has two
*phases of the same substance, for
example solid and liquid, heat is
added or taken away very slowly so
that one phase can change reversibly
into the other while the system remains at equilibrium. If the two
phases are denoted A and B, the
Clapeyron–Clausius equation is:
dp/dT = L/T(V B –V A ),
where p is the pressure, T is the thermodynamic temperature, L is the
heat absorbed per mole in the
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