insecticides, and wood preservatives,
and in making dyes. They form condensation polymers of the bakelite
type with methanal.
chlorophyll One of a number of
pigments, including (chlorophyll a
and chlorophyll b), that are responsible for the green colour of most
plants. Chlorophyll molecules are the
principal sites of light absorption in
the light-dependent reactions of
*photosynthesis. They are magnesium-containing *porphyrins, chemically related to *cytochrome and
*haemoglobin.
123
chromatogram
c
CHCH 2
CH 3
C 2 H 5
CH CH CH
CH 3
CO
CH CH CH
C C C
COOCH 3
COOCH 3
COOCH 3
C 20 H 39 O
C C C
O
CH 2
CH 2
CH 2
CH 2
CH 2
CH 2
CH 3
H
H
N N N
N N N
Mg Mg Mg
N N N
N N N
CH CH CH
CH 3
CH CH CH
hydrocarbon
(phytol) chain
Chlorophyll
chloroplatinic acid A reddish crystalline compound, H 2 PtCl 6 , made by
dissolving platinum in aqua regia.
chloroprene See 2-chlorobuta-1,3diene.
chlorosulphanes See disulphur
dichloride.
chlorous acid See chloric(iii) acid.
choke damp See blackdamp.
cholecalciferol See vitamin d.
cholesteric crystal A type of *liquid crystal in which molecules lie in
sheets at angles that change by a
small amount between each sheet.
The pitch of the helix so formed is
similar to the wavelength of visible
light. Cholesteric liquid crystals
therefore diffract light and have
colours that depend on the temperature. (The word cholesteric is derived
from the Greek for bile solid.)
cholesterol A *sterol occurring
widely in animal tissues and also in
some higher plants and algae. It can
exist as a free sterol or esteriÜed with
a long-chain fatty acid. Cholesterol is
absorbed through the intestine or
manufactured in the liver. It serves
principally as a constituent of blood
plasma lipoproteins and of the
lipid–protein complexes that form
cell membranes. It is also important
as a precursor of various steroids, especially the bile acids, sex hormones,
and adrenocorticoid hormones. The
derivative 7-dehydrocholesterol is
converted to vitamin D 3 by the action
of sunlight on skin. Increased levels
of dietary and blood cholesterol have
been associated with atherosclerosis,
a condition in which lipids accumulate on the inner walls of arteries and
eventually obstruct blood Ûow.
choline An amino alcohol,
CH 2 OHCH 2 N(CH 3 ) 3 OH. It occurs
widely in living organisms as a
constituent of certain types of
phospholipids – the lecithins and
sphingomyelins – and in the neurotransmitter *acetylcholine. It is
sometimes classiÜed as a member
of the vitamin B complex.
chromate A salt containing the ion
CrO 4
2– .
chromatogram A record obtained
by *chromatography. The term is applied to the developed records of
*paper chromatography and *thinlayer chromatography and also to the
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and in making dyes. They form condensation polymers of the bakelite
type with methanal.
chlorophyll One of a number of
pigments, including (chlorophyll a
and chlorophyll b), that are responsible for the green colour of most
plants. Chlorophyll molecules are the
principal sites of light absorption in
the light-dependent reactions of
*photosynthesis. They are magnesium-containing *porphyrins, chemically related to *cytochrome and
*haemoglobin.
123
chromatogram
c
CHCH 2
CH 3
C 2 H 5
CH CH CH
CH 3
CO
CH CH CH
C C C
COOCH 3
COOCH 3
COOCH 3
C 20 H 39 O
C C C
O
CH 2
CH 2
CH 2
CH 2
CH 2
CH 2
CH 3
H
H
N N N
N N N
Mg Mg Mg
N N N
N N N
CH CH CH
CH 3
CH CH CH
hydrocarbon
(phytol) chain
Chlorophyll
chloroplatinic acid A reddish crystalline compound, H 2 PtCl 6 , made by
dissolving platinum in aqua regia.
chloroprene See 2-chlorobuta-1,3diene.
chlorosulphanes See disulphur
dichloride.
chlorous acid See chloric(iii) acid.
choke damp See blackdamp.
cholecalciferol See vitamin d.
cholesteric crystal A type of *liquid crystal in which molecules lie in
sheets at angles that change by a
small amount between each sheet.
The pitch of the helix so formed is
similar to the wavelength of visible
light. Cholesteric liquid crystals
therefore diffract light and have
colours that depend on the temperature. (The word cholesteric is derived
from the Greek for bile solid.)
cholesterol A *sterol occurring
widely in animal tissues and also in
some higher plants and algae. It can
exist as a free sterol or esteriÜed with
a long-chain fatty acid. Cholesterol is
absorbed through the intestine or
manufactured in the liver. It serves
principally as a constituent of blood
plasma lipoproteins and of the
lipid–protein complexes that form
cell membranes. It is also important
as a precursor of various steroids, especially the bile acids, sex hormones,
and adrenocorticoid hormones. The
derivative 7-dehydrocholesterol is
converted to vitamin D 3 by the action
of sunlight on skin. Increased levels
of dietary and blood cholesterol have
been associated with atherosclerosis,
a condition in which lipids accumulate on the inner walls of arteries and
eventually obstruct blood Ûow.
choline An amino alcohol,
CH 2 OHCH 2 N(CH 3 ) 3 OH. It occurs
widely in living organisms as a
constituent of certain types of
phospholipids – the lecithins and
sphingomyelins – and in the neurotransmitter *acetylcholine. It is
sometimes classiÜed as a member
of the vitamin B complex.
chromate A salt containing the ion
CrO 4
2– .
chromatogram A record obtained
by *chromatography. The term is applied to the developed records of
*paper chromatography and *thinlayer chromatography and also to the
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