linear combination of atomic
orbitals See lcao.
linear molecule A molecule in
which the atoms are in a straight
line, as in carbon dioxide, O=C=O.
Linear molecules have only two rotational degrees of freedom.
linear rotor See moment of inertia.
line notation A notation system
for writing the structure of a chemical compound as a string of letters,
numbers, and symbols. Examples of
line notation are *Wiswesser line notation (WLN), *SMILES, *SYBYL line
notation (SLN), *ROSDAL, and
*InChI.
line spectrum See spectrum.
linoleic acid A liquid polyunsaturated *fatty acid with two double
bonds, CH 3 (CH 2 ) 4 CH:CHCH 2 -
CH:CH(CH 2 ) 7 COOH. Linoleic acid is
abundant in plant fats and oils, e.g.
linseed oil, groundnut oil, and soyabean oil. It is an *essential fatty acid.
linolenic acid A liquid polyunsaturated *fatty acid with three double
bonds in its structure:
CH 3 CH 2 CH:CHCH 2 CH:CHCH 2 CH:CH(CH 2 ) 7 COOH. It occurs in certain
plant oils, e.g. linseed and soya-bean
oil, and in algae. It is one of the *essential fatty acids.
linseed oil A pale yellow oil
pressed from Ûax seed. It contains a
mixture of glycerides of fatty acids,
including linoleic acid and linolenic
acid. It is a *drying oil, used in oil
paints, varnishes, linoleum, etc.
Linz–Donawitz process See basicoxygen process.
lipase An enzyme secreted by the
pancreas and the glands of the small
intestine of vertebrates that catalyses
the breakdown of fats into fatty acids
and glycerol.
lipid Any of a diverse group of organic compounds, occurring in living
organisms, that are insoluble in
water but soluble in organic solvents,
such as chloroform, benzene, etc.
Lipids are broadly classiÜed into two
categories: complex lipids, which are
esters of long-chain fatty acids and
include the *glycerides (which constitute the *fats and *oils of animals
and plants), *glycolipids, *phospholipids, and *waxes; and simple lipids,
which do not contain fatty acids and
include the *steroids and *terpenes.
Lipids have a variety of functions in
living organisms. Fats and oils are a
convenient and concentrated means
of storing food energy in plants and
animals. Phospholipids and *sterols,
such as cholesterol, are major components of cell membranes (see lipid
bilayer). Waxes provide vital waterprooÜng for body surfaces. Terpenes
include vitamins A, E, and K, and
phytol (a component of chlorophyll)
and occur in essential oils, such as
menthol and camphor. Steroids include the adrenal hormones, sex hormones, and bile acids.
Lipids can combine with proteins
to form lipoproteins, e.g. in cell
membranes. In bacterial cell walls,
lipids may associate with polysaccharides to form lipopolysaccharides.
A
• Information about IUPAC nomenclature
of lipids
lipid bilayer The arrangement of
lipid molecules in biological membranes, which takes the form of a
double sheet. Each lipid molecule
comprises a hydrophilic ‘head’ (having a high afÜnity for water) and a
hydrophobic ‘tail’ (having a low
afÜnity for water). In the lipid bilayer
the molecules are aligned so that
their hydrophilic heads face outwards, forming the outer and inner
surfaces of the membrane, while the
327
lipid bilayer
l
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orbitals See lcao.
linear molecule A molecule in
which the atoms are in a straight
line, as in carbon dioxide, O=C=O.
Linear molecules have only two rotational degrees of freedom.
linear rotor See moment of inertia.
line notation A notation system
for writing the structure of a chemical compound as a string of letters,
numbers, and symbols. Examples of
line notation are *Wiswesser line notation (WLN), *SMILES, *SYBYL line
notation (SLN), *ROSDAL, and
*InChI.
line spectrum See spectrum.
linoleic acid A liquid polyunsaturated *fatty acid with two double
bonds, CH 3 (CH 2 ) 4 CH:CHCH 2 -
CH:CH(CH 2 ) 7 COOH. Linoleic acid is
abundant in plant fats and oils, e.g.
linseed oil, groundnut oil, and soyabean oil. It is an *essential fatty acid.
linolenic acid A liquid polyunsaturated *fatty acid with three double
bonds in its structure:
CH 3 CH 2 CH:CHCH 2 CH:CHCH 2 CH:CH(CH 2 ) 7 COOH. It occurs in certain
plant oils, e.g. linseed and soya-bean
oil, and in algae. It is one of the *essential fatty acids.
linseed oil A pale yellow oil
pressed from Ûax seed. It contains a
mixture of glycerides of fatty acids,
including linoleic acid and linolenic
acid. It is a *drying oil, used in oil
paints, varnishes, linoleum, etc.
Linz–Donawitz process See basicoxygen process.
lipase An enzyme secreted by the
pancreas and the glands of the small
intestine of vertebrates that catalyses
the breakdown of fats into fatty acids
and glycerol.
lipid Any of a diverse group of organic compounds, occurring in living
organisms, that are insoluble in
water but soluble in organic solvents,
such as chloroform, benzene, etc.
Lipids are broadly classiÜed into two
categories: complex lipids, which are
esters of long-chain fatty acids and
include the *glycerides (which constitute the *fats and *oils of animals
and plants), *glycolipids, *phospholipids, and *waxes; and simple lipids,
which do not contain fatty acids and
include the *steroids and *terpenes.
Lipids have a variety of functions in
living organisms. Fats and oils are a
convenient and concentrated means
of storing food energy in plants and
animals. Phospholipids and *sterols,
such as cholesterol, are major components of cell membranes (see lipid
bilayer). Waxes provide vital waterprooÜng for body surfaces. Terpenes
include vitamins A, E, and K, and
phytol (a component of chlorophyll)
and occur in essential oils, such as
menthol and camphor. Steroids include the adrenal hormones, sex hormones, and bile acids.
Lipids can combine with proteins
to form lipoproteins, e.g. in cell
membranes. In bacterial cell walls,
lipids may associate with polysaccharides to form lipopolysaccharides.
A
• Information about IUPAC nomenclature
of lipids
lipid bilayer The arrangement of
lipid molecules in biological membranes, which takes the form of a
double sheet. Each lipid molecule
comprises a hydrophilic ‘head’ (having a high afÜnity for water) and a
hydrophobic ‘tail’ (having a low
afÜnity for water). In the lipid bilayer
the molecules are aligned so that
their hydrophilic heads face outwards, forming the outer and inner
surfaces of the membrane, while the
327
lipid bilayer
l
www.AzShimi.ir www.AzShimi.com