analysed by the *Debye– Hückel–Onsager theory.
Kohlrausch’s law If a salt is dissolved in water, the conductivity of
the (dilute) solution is the sum of two
values – one depending on the positive ions and the other on the negative ions. The law, which depends on
the independent migration of ions,
was deduced experimentally by
Friedrich Kohlrausch.
Kolbe’s method A method of
making alkanes by electrolysing a solution of a carboxylic acid salt. For a
salt Na
+ RCOO
–
, the carboxylate ions
lose electrons at the cathode to give
radicals:
RCOO
– – e → RCOO .
These decompose to give alkyl radicals
RCOO . → R . + CO 2
Two alkyl radicals couple to give an
alkane
R . + R . → RR
The method can only be used for hydrocarbons with an even number of
carbon atoms, although mixtures of
two salts can be electrolysed to give a
mixture of three products. The
method was discovered by the German chemist Herman Kolbe
(1818–84), who electrolysed pentanoic acid (C 4 H 9 COOH) in 1849 and
obtained a hydrocarbon, which he assumed was the substance ‘butyl’
C 4 H 9 (actually octane, C 8 H 18 ).
Koopmans’ theorem The principle that the ionization energy of a
molecule is equal to the orbital energy of the ejected electron. It is the
basis of the interpretation of spectra
in *photoelectron spectroscopy.
Koopmans’ theorem is an approximation in that it ignores any reorganization of electrons in the ion formed. It
is named after the Dutch mathematician and economist Tjalling Charles
Koopmans (1910–85).
Kovar A tradename for an alloy of
iron, cobalt, and nickel with an expansivity similar to that of glass. It is
therefore used in making glass-tometal seals, especially in circumstances in which a temperature
variation can be expected.
Kramers theorem The energy levels of a system, such as an atom that
contains an odd number of spin-½
particles (e.g. electrons), are at least
double *degenerate in the absence of
an external magnetic Üeld. This degeneracy, known as Kramers degeneracy, is a consequence of time
reversal invariance. Kramers theorem
was stated by the Dutch physicist
Hendrick Anton Kramers (1894–1952)
in 1930. Kramers degeneracy is removed by placing the system in an
external magnetic Üeld. The theorem
holds even in the presence of crystal
Üelds (see crystal-field theory) and
*spin–orbit coupling.
Krebs, Sir Hans Adolf (1900–81)
German-born British biochemist,
who emigrated to Britain in 1933,
working at ShefÜeld University before moving to Oxford in 1954.
Krebs is best known for the *Krebs
cycle, the basis of which he discovered in 1937. Details were later
added by Fritz Lipmann (1899–1986),
with whom Krebs shared the 1953
Nobel Prize for physiology or medicine.
Krebs cycle (citric acid cycle; tricarboxylic acid cycle; TCA cycle) A
cyclical series of biochemical reactions that is fundamental to the
metabolism of aerobic organisms, i.e.
animals, plants, and many microorganisms (see illustration). The enzymes of the Krebs cycle are located
in the mitochondria and are in close
association with the components of
Kohlrausch’s law
308
k
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Kohlrausch’s law If a salt is dissolved in water, the conductivity of
the (dilute) solution is the sum of two
values – one depending on the positive ions and the other on the negative ions. The law, which depends on
the independent migration of ions,
was deduced experimentally by
Friedrich Kohlrausch.
Kolbe’s method A method of
making alkanes by electrolysing a solution of a carboxylic acid salt. For a
salt Na
+ RCOO
–
, the carboxylate ions
lose electrons at the cathode to give
radicals:
RCOO
– – e → RCOO .
These decompose to give alkyl radicals
RCOO . → R . + CO 2
Two alkyl radicals couple to give an
alkane
R . + R . → RR
The method can only be used for hydrocarbons with an even number of
carbon atoms, although mixtures of
two salts can be electrolysed to give a
mixture of three products. The
method was discovered by the German chemist Herman Kolbe
(1818–84), who electrolysed pentanoic acid (C 4 H 9 COOH) in 1849 and
obtained a hydrocarbon, which he assumed was the substance ‘butyl’
C 4 H 9 (actually octane, C 8 H 18 ).
Koopmans’ theorem The principle that the ionization energy of a
molecule is equal to the orbital energy of the ejected electron. It is the
basis of the interpretation of spectra
in *photoelectron spectroscopy.
Koopmans’ theorem is an approximation in that it ignores any reorganization of electrons in the ion formed. It
is named after the Dutch mathematician and economist Tjalling Charles
Koopmans (1910–85).
Kovar A tradename for an alloy of
iron, cobalt, and nickel with an expansivity similar to that of glass. It is
therefore used in making glass-tometal seals, especially in circumstances in which a temperature
variation can be expected.
Kramers theorem The energy levels of a system, such as an atom that
contains an odd number of spin-½
particles (e.g. electrons), are at least
double *degenerate in the absence of
an external magnetic Üeld. This degeneracy, known as Kramers degeneracy, is a consequence of time
reversal invariance. Kramers theorem
was stated by the Dutch physicist
Hendrick Anton Kramers (1894–1952)
in 1930. Kramers degeneracy is removed by placing the system in an
external magnetic Üeld. The theorem
holds even in the presence of crystal
Üelds (see crystal-field theory) and
*spin–orbit coupling.
Krebs, Sir Hans Adolf (1900–81)
German-born British biochemist,
who emigrated to Britain in 1933,
working at ShefÜeld University before moving to Oxford in 1954.
Krebs is best known for the *Krebs
cycle, the basis of which he discovered in 1937. Details were later
added by Fritz Lipmann (1899–1986),
with whom Krebs shared the 1953
Nobel Prize for physiology or medicine.
Krebs cycle (citric acid cycle; tricarboxylic acid cycle; TCA cycle) A
cyclical series of biochemical reactions that is fundamental to the
metabolism of aerobic organisms, i.e.
animals, plants, and many microorganisms (see illustration). The enzymes of the Krebs cycle are located
in the mitochondria and are in close
association with the components of
Kohlrausch’s law
308
k
www.AzShimi.ir www.AzShimi.com