that is used illegally as a club drug. It
is a class A drug in the UK.
ketene (keten) 1. The compound
CH 2 =C=O (ethenone). It can be prepared by pyrolysis of propanone. The
compound reacts readily with compounds containing hydroxyl or
amino groups and is used as an acetylating agent. 2. Any of a class of
compounds of the type R 1 R 2 =C=O,
where R 1 and R 2 are organic groups.
Ketenes are reactive compounds and
are often generated in a reaction
medium for organic synthesis.
A
• Information about IUPAC nomenclature
keto–enol tautomerism A form
of tautomerism in which a compound containing a –CH 2 –CO– group
(the keto form of the molecule) is in
equilibrium with one containing the
–CH=C(OH)– group (the enol). It occurs by migration of a hydrogen
atom between a carbon atom and the
oxygen on an adjacent carbon. See
isomerism.
keto form See keto–enol tautomerism.
ketohexose See monosaccharide.
ketol An organic compound that
has both an alcohol (-CH 2 OH) and a
keto (=CO) group. Ketols are made by
a condensation reaction between two
ketones or by the oxidation of dihydric alcohols (glycols).
ketone body Any of three compounds, acetoacetic acid (3-oxobutanoic acid, CH 3 COCH 2 COOH),
β-hydroxybutyric acid (3-hydroxybutanoic acid, CH 3 CH(OH)CH 2 COOH),
and acetone or (propanone,
CH 3 COCH 3 ), produced by the liver as
a result of the metabolism of body
fat deposits. Ketone bodies are normally used as energy sources by peripheral tissues.
ketones Organic compounds that
contain the carbonyl group (>C=O)
linked to two hydrocarbon groups.
The ketone group is a carbonyl group
with two single bonds to other carbon atoms. In systematic chemical
nomenclature, ketone names end
with the sufÜx -one. Examples are
propanone (acetone), CH 3 COCH 3 , and
butanone (methyl ethyl ketone),
CH 3 COC 2 H 5 . Ketones can be made by
oxidizing secondary alcohols to convert the C–OH group to C=O. Certain
ketones form addition compounds
with sodium hydrogensulphate(IV)
(sodium hydrogensulphite). They also
form addition compounds with hydrogen cyanide to give *cyanohydrins and with alcohols to give
*ketals. They undergo condensation
reactions to yield *oximes, *hydrazones, phenylhydrazones, and *semicarbazones. These are reactions that
they share with aldehydes. Unlike
aldehydes, they do not affect
Fehling’s solution or Tollens reagent
and do not easily oxidize. Strong oxidizing agents produce a mixture of
carboxylic acids; butanone, for example, gives ethanoic and propanoic
acids.
A
• Information about IUPAC nomenclature
ketopentose See monosaccharide.
ketose See monosaccharide.
khat A plant, Catha edilis, found in
East Africa and the Arabian peninsular. The leaves are chewed to give a
mildly stimulating and euphoric effect. Its activity comes from two alkaloids: *cathine and, in fresh leaves,
the more potent *cathinone. It is a
controlled substance in many countries including the US. In the UK it is
not a controlled substance and is
used by certain Somalian and Yemeni
ethnic groups.
kieselguhr (diatomaceous earth; diketene
304
k
www.AzShimi.ir www.AzShimi.com
is a class A drug in the UK.
ketene (keten) 1. The compound
CH 2 =C=O (ethenone). It can be prepared by pyrolysis of propanone. The
compound reacts readily with compounds containing hydroxyl or
amino groups and is used as an acetylating agent. 2. Any of a class of
compounds of the type R 1 R 2 =C=O,
where R 1 and R 2 are organic groups.
Ketenes are reactive compounds and
are often generated in a reaction
medium for organic synthesis.
A
• Information about IUPAC nomenclature
keto–enol tautomerism A form
of tautomerism in which a compound containing a –CH 2 –CO– group
(the keto form of the molecule) is in
equilibrium with one containing the
–CH=C(OH)– group (the enol). It occurs by migration of a hydrogen
atom between a carbon atom and the
oxygen on an adjacent carbon. See
isomerism.
keto form See keto–enol tautomerism.
ketohexose See monosaccharide.
ketol An organic compound that
has both an alcohol (-CH 2 OH) and a
keto (=CO) group. Ketols are made by
a condensation reaction between two
ketones or by the oxidation of dihydric alcohols (glycols).
ketone body Any of three compounds, acetoacetic acid (3-oxobutanoic acid, CH 3 COCH 2 COOH),
β-hydroxybutyric acid (3-hydroxybutanoic acid, CH 3 CH(OH)CH 2 COOH),
and acetone or (propanone,
CH 3 COCH 3 ), produced by the liver as
a result of the metabolism of body
fat deposits. Ketone bodies are normally used as energy sources by peripheral tissues.
ketones Organic compounds that
contain the carbonyl group (>C=O)
linked to two hydrocarbon groups.
The ketone group is a carbonyl group
with two single bonds to other carbon atoms. In systematic chemical
nomenclature, ketone names end
with the sufÜx -one. Examples are
propanone (acetone), CH 3 COCH 3 , and
butanone (methyl ethyl ketone),
CH 3 COC 2 H 5 . Ketones can be made by
oxidizing secondary alcohols to convert the C–OH group to C=O. Certain
ketones form addition compounds
with sodium hydrogensulphate(IV)
(sodium hydrogensulphite). They also
form addition compounds with hydrogen cyanide to give *cyanohydrins and with alcohols to give
*ketals. They undergo condensation
reactions to yield *oximes, *hydrazones, phenylhydrazones, and *semicarbazones. These are reactions that
they share with aldehydes. Unlike
aldehydes, they do not affect
Fehling’s solution or Tollens reagent
and do not easily oxidize. Strong oxidizing agents produce a mixture of
carboxylic acids; butanone, for example, gives ethanoic and propanoic
acids.
A
• Information about IUPAC nomenclature
ketopentose See monosaccharide.
ketose See monosaccharide.
khat A plant, Catha edilis, found in
East Africa and the Arabian peninsular. The leaves are chewed to give a
mildly stimulating and euphoric effect. Its activity comes from two alkaloids: *cathine and, in fresh leaves,
the more potent *cathinone. It is a
controlled substance in many countries including the US. In the UK it is
not a controlled substance and is
used by certain Somalian and Yemeni
ethnic groups.
kieselguhr (diatomaceous earth; diketene
304
k
www.AzShimi.ir www.AzShimi.com