chirality The property of existing
in left- and right-handed structural
forms. See optical activity.
chirality element The part of a
molecule that makes it exist in leftand right-handed forms. In most
cases this is a chirality centre (i.e. an
asymmetric atom). In certain cases
the element is a chirality axis. For example, in allenenes of the type
R 1 R 2 C=C=CR 3 R 4 the C=C=C chain is a
chirality axis. Certain ring compounds may display chirality as a result of a chirality plane in the
molecule.
chirooptical spectroscopy Spectroscopy making use of the properties of chiral substances when they
interact with polarized light of various wavelengths. Optical rotatory
dispersion (the change of optical rotation with wavelength) and *circular
dichroism are old examples of chirooptical spectroscopy. More recent
types of chirooptical spectroscopy are
vibrational optical rotatory dispersion, vibrational circular dichroism.
(VCD), and Raman optical activity
(ROA), which are all the result of
the interaction between chiral substances and polarized infrared
electromagnetic radiation; these
techniques are known as vibrational
optical activity (VOA), as they are associated with transitions in the vibrational energy levels in the electronic
ground state of a molecule. Chirooptical spectroscopy is used in the
analysis of the structure of molecules.
chitin A *polysaccharide comprising chains of N-acetyl-d-glucosamine,
a derivative of glucose. Chitin is
structurally very similar to cellulose
and serves to strengthen the supporting structures of various invertebrates. It also occurs in fungi.
chloral See trichloroethanal.
chloral hydrate See 2,2,2trichloroethanediol.
chlorates Salts of the chloric acids;
i.e. salts containing the ions ClO
–
(chlorate(I) or hypochlorite), ClO 2
–
(chlorate(III) or chlorite), ClO 3
– (chlorate(V)), or ClO 4
– (chlorate(VII) or perchlorate). When used without
speciÜcation of an oxidation state the
term ‘chlorate’ refers to a chlorate(V)
salt.
chloric acid Any of the oxoacids of
chlorine: *chloric(I) acid, *chloric(III)
acid, *chloric(V) acid, and
*chloric(VII) acid. The term is commonly used without speciÜcation of
the oxidation state of chlorine to
mean chloric(V) acid, HClO 3 .
chloric(I) acid (hypochlorous acid)
A liquid acid that is stable only in solution, HOCl. It may be prepared by
the reaction of chlorine with an agitated suspension of mercury(II) oxide.
Because the disproportionation of
the ion ClO
– is slow at low temperatures chloric(I) acid may be produced,
along with chloride ions by the reaction of chlorine with water at 0°C. At
higher temperatures disproportionation to the chlorate(V) ion, ClO 3
–
,
takes place. Chloric(I) acid is a very
weak acid but is a mild oxidizing
agent and is widely used as a bleaching agent.
chloric(III) acid (chlorous acid) A
pale-yellow acid known only in solution, HClO 2 . It is formed by the reaction of chlorine dioxide and water
and is a weak acid and an oxidizing
agent.
chloric(V) acid (chloric acid) A
colourless unstable liquid, HClO 3 ; r.d.
1.2; m.p. <–20°C; decomposes at
40°C. It is best prepared by the reaction of barium chlorate with sulphuric acid although chloric(V) acid
is also formed by the disproportionachirality
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in left- and right-handed structural
forms. See optical activity.
chirality element The part of a
molecule that makes it exist in leftand right-handed forms. In most
cases this is a chirality centre (i.e. an
asymmetric atom). In certain cases
the element is a chirality axis. For example, in allenenes of the type
R 1 R 2 C=C=CR 3 R 4 the C=C=C chain is a
chirality axis. Certain ring compounds may display chirality as a result of a chirality plane in the
molecule.
chirooptical spectroscopy Spectroscopy making use of the properties of chiral substances when they
interact with polarized light of various wavelengths. Optical rotatory
dispersion (the change of optical rotation with wavelength) and *circular
dichroism are old examples of chirooptical spectroscopy. More recent
types of chirooptical spectroscopy are
vibrational optical rotatory dispersion, vibrational circular dichroism.
(VCD), and Raman optical activity
(ROA), which are all the result of
the interaction between chiral substances and polarized infrared
electromagnetic radiation; these
techniques are known as vibrational
optical activity (VOA), as they are associated with transitions in the vibrational energy levels in the electronic
ground state of a molecule. Chirooptical spectroscopy is used in the
analysis of the structure of molecules.
chitin A *polysaccharide comprising chains of N-acetyl-d-glucosamine,
a derivative of glucose. Chitin is
structurally very similar to cellulose
and serves to strengthen the supporting structures of various invertebrates. It also occurs in fungi.
chloral See trichloroethanal.
chloral hydrate See 2,2,2trichloroethanediol.
chlorates Salts of the chloric acids;
i.e. salts containing the ions ClO
–
(chlorate(I) or hypochlorite), ClO 2
–
(chlorate(III) or chlorite), ClO 3
– (chlorate(V)), or ClO 4
– (chlorate(VII) or perchlorate). When used without
speciÜcation of an oxidation state the
term ‘chlorate’ refers to a chlorate(V)
salt.
chloric acid Any of the oxoacids of
chlorine: *chloric(I) acid, *chloric(III)
acid, *chloric(V) acid, and
*chloric(VII) acid. The term is commonly used without speciÜcation of
the oxidation state of chlorine to
mean chloric(V) acid, HClO 3 .
chloric(I) acid (hypochlorous acid)
A liquid acid that is stable only in solution, HOCl. It may be prepared by
the reaction of chlorine with an agitated suspension of mercury(II) oxide.
Because the disproportionation of
the ion ClO
– is slow at low temperatures chloric(I) acid may be produced,
along with chloride ions by the reaction of chlorine with water at 0°C. At
higher temperatures disproportionation to the chlorate(V) ion, ClO 3
–
,
takes place. Chloric(I) acid is a very
weak acid but is a mild oxidizing
agent and is widely used as a bleaching agent.
chloric(III) acid (chlorous acid) A
pale-yellow acid known only in solution, HClO 2 . It is formed by the reaction of chlorine dioxide and water
and is a weak acid and an oxidizing
agent.
chloric(V) acid (chloric acid) A
colourless unstable liquid, HClO 3 ; r.d.
1.2; m.p. <–20°C; decomposes at
40°C. It is best prepared by the reaction of barium chlorate with sulphuric acid although chloric(V) acid
is also formed by the disproportionachirality
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