reaction of alcohols with sodium or
potassium metal. Alkoxides are saltlike compounds containing the ion
R–O
– .
alkyd resin A type of *polyester
resin used in paints and other surface coating. The original alkyd
resins were made by copolymerizing
phthalic anhydride with glycerol, to
give a brittle cross-linked polymer.
The properties of such resins can be
modiÜed by adding monobasic acids
or alcohols during the polymerization.
alkylation A chemical reaction
that introduces an *alkyl group into
an organic molecule. The *Friedel–
Crafts reaction results in alkylation
of aromatic compounds.
alkylbenzenes Organic compounds that have an alkyl group
bound to a benzene ring. The simplest example is methylbenzene
(toluene), CH 3 C 6 H 5 . Alkyl benzenes
can be made by the *Friedel–Crafts
reaction.
alkyl group A group obtained by
removing a hydrogen atom from an
alkane, e.g. methyl group, CH 3 –, derived from methane.
alkyl halides See haloalkanes.
alkynes (acetylenes) Unsaturated
hydrocarbons that contain one or
more triple carbon–carbon bonds in
their molecules. In systematic chemical nomenclature alkyne names end
in the sufÜx -yne. Alkynes that have
only one triple bond form a *homologous series: ethyne (acetylene),
CH≡CH, propyne, CH 3 CH≡CH, etc.
They can be made by the action of
potassium hydroxide in alcohol solution on haloalkanes containing halogen atoms on adjacent carbon atoms;
for example:
RCHClCH 2 Cl + 2KOH → 2KCl +
2H 2 O + RCH≡CH
Like *alkenes, alkynes undergo addition reactions.
A
• Information about IUPAC nomenclature
allenes Compounds that contain
the group >C=C=C<, in which three
carbon atoms are linked by two adjacent double bonds. The outer carbon
atoms are each linked to two other
atoms or groups by single bonds. The
simplest example is 1,2-propadiene,
CH 2 CCH 2 . Allenes are *dienes with
typical reactions of alkenes. Under
basic conditions, they often convert
to alkynes. In an allene, the two
double bonds lie in planes that are
perpendicular to each other. Consequently, in an allene of the type
R 1 R 2 C:C:CR 3 R 4 , the groups R 1 and
R 2 lie in a plane perpendicular to
the plane containing R 3 and R 4 .
Under these circumstances, the molecule is chiral and can show optical
activity.
allosteric enzyme An enzyme
that has two structurally distinct
forms, one of which is active and the
other inactive. In the active form, the
quaternary structure (see protein) of
the enzyme is such that a substrate
can interact with the enzyme at the
active site (see enzyme–substrate
complex). The conformation of the
substrate-binding site becomes altered in the inactive form and interaction with the substrate is not
possible. Allosteric enzymes tend to
catalyse the initial step in a pathway
leading to the synthesis of molecules.
The end product of this synthesis can
act as a feedback inhibitor (see inhibition) and the enzyme is converted to
the inactive form, thereby controlling the amount of product synthesized.
allosteric site A binding site on
the surface of an enzyme other than
the *active site. In noncompetitive
21
allosteric site
a
www.AzShimi.ir www.AzShimi.com
potassium metal. Alkoxides are saltlike compounds containing the ion
R–O
– .
alkyd resin A type of *polyester
resin used in paints and other surface coating. The original alkyd
resins were made by copolymerizing
phthalic anhydride with glycerol, to
give a brittle cross-linked polymer.
The properties of such resins can be
modiÜed by adding monobasic acids
or alcohols during the polymerization.
alkylation A chemical reaction
that introduces an *alkyl group into
an organic molecule. The *Friedel–
Crafts reaction results in alkylation
of aromatic compounds.
alkylbenzenes Organic compounds that have an alkyl group
bound to a benzene ring. The simplest example is methylbenzene
(toluene), CH 3 C 6 H 5 . Alkyl benzenes
can be made by the *Friedel–Crafts
reaction.
alkyl group A group obtained by
removing a hydrogen atom from an
alkane, e.g. methyl group, CH 3 –, derived from methane.
alkyl halides See haloalkanes.
alkynes (acetylenes) Unsaturated
hydrocarbons that contain one or
more triple carbon–carbon bonds in
their molecules. In systematic chemical nomenclature alkyne names end
in the sufÜx -yne. Alkynes that have
only one triple bond form a *homologous series: ethyne (acetylene),
CH≡CH, propyne, CH 3 CH≡CH, etc.
They can be made by the action of
potassium hydroxide in alcohol solution on haloalkanes containing halogen atoms on adjacent carbon atoms;
for example:
RCHClCH 2 Cl + 2KOH → 2KCl +
2H 2 O + RCH≡CH
Like *alkenes, alkynes undergo addition reactions.
A
• Information about IUPAC nomenclature
allenes Compounds that contain
the group >C=C=C<, in which three
carbon atoms are linked by two adjacent double bonds. The outer carbon
atoms are each linked to two other
atoms or groups by single bonds. The
simplest example is 1,2-propadiene,
CH 2 CCH 2 . Allenes are *dienes with
typical reactions of alkenes. Under
basic conditions, they often convert
to alkynes. In an allene, the two
double bonds lie in planes that are
perpendicular to each other. Consequently, in an allene of the type
R 1 R 2 C:C:CR 3 R 4 , the groups R 1 and
R 2 lie in a plane perpendicular to
the plane containing R 3 and R 4 .
Under these circumstances, the molecule is chiral and can show optical
activity.
allosteric enzyme An enzyme
that has two structurally distinct
forms, one of which is active and the
other inactive. In the active form, the
quaternary structure (see protein) of
the enzyme is such that a substrate
can interact with the enzyme at the
active site (see enzyme–substrate
complex). The conformation of the
substrate-binding site becomes altered in the inactive form and interaction with the substrate is not
possible. Allosteric enzymes tend to
catalyse the initial step in a pathway
leading to the synthesis of molecules.
The end product of this synthesis can
act as a feedback inhibitor (see inhibition) and the enzyme is converted to
the inactive form, thereby controlling the amount of product synthesized.
allosteric site A binding site on
the surface of an enzyme other than
the *active site. In noncompetitive
21
allosteric site
a
www.AzShimi.ir www.AzShimi.com