is ionized for a given frequency it has
many applications in chemistry.
resorcinol See 1,3-dihydroxybenzene.
retinol See vitamin a.
retort 1. A laboratory apparatus
consisting of a glass bulb with a long
neck. 2. A vessel used for reaction or
distillation in industrial chemical
processes.
retrosynthetic analysis A technique for planning the series of reactions required to synthesize a given
molecule. It involves working backwards from the known structure. The
molecule to be synthesized (the target molecule) is considered to be split
into two parts (a process called disconnection). The parts are not themselves molecules, but are fragments
(called synthons) that correspond to
actual reagents. A trivial example
would be the synthesis of the target
molecule
R
1
–O–CO–R
2
This is an ester. A suitable disconnection is at the O–CO bond, giving two
synthons,
R
1
–O– and R
2
C(O)–.
The convention is to write this in the
form
R
1
–O–C(O)– R
2
⇒ R
1 –O– + R
2 –C(O)–.
Here the symbol is a logic symbol for
‘implies’; it is called the retrosynthetic arrow. In this example, suitable reagents corresponding to these
synthons would be an alcohol R
1 OH
and an acyl chloride R
2
COCl. Note
that the disconnection is always
made at a point corresponding to a
known reaction. In actual schemes,
the target molecules are complex
and a number of retrosynthetic steps
are needed.
reverberatory furnace A metallurgical furnace in which the charge
to be heated is kept separate from
the fuel. It consists of a shallow
hearth on which the charge is heated
by Ûames that pass over it and by radiation reÛected onto it from a low
roof.
reverse osmosis A method of obtaining pure water from water containing a salt, as in *desalination.
Pure water and the salt water are
separated by a semipermeable membrane and the pressure of the salt
water is raised above the osmotic
pressure, causing water from the
brine to pass through the membrane
into the pure water. This process requires a pressure of some 25 atmospheres, which makes it difÜcult to
apply on a large scale.
reversible process Any process in
which the variables that deÜne the
state of the system can be made to
change in such a way that they pass
through the same values in the reverse order when the process is reversed. It is also a condition of a
reversible process that any exchanges of energy, work, or matter
with the surroundings should be reversed in direction and order when
the process is reversed. Any process
that does not comply with these conditions when it is reversed is said to
be an irreversible process. All natural
processes are irreversible, although
some processes can be made to approach closely to a reversible process.
R F value (in chromatography) The
distance travelled by a given component divided by the distance travelled by the solvent front. For a given
system at a known temperature, it is
a characteristic of the component
and can be used to identify components.
rhe A unit of Ûuidity equal to the
reciprocal of the *poise.
rhenium Symbol Re. A silveryresorcinol
460
r
www.AzShimi.ir www.AzShimi.com
many applications in chemistry.
resorcinol See 1,3-dihydroxybenzene.
retinol See vitamin a.
retort 1. A laboratory apparatus
consisting of a glass bulb with a long
neck. 2. A vessel used for reaction or
distillation in industrial chemical
processes.
retrosynthetic analysis A technique for planning the series of reactions required to synthesize a given
molecule. It involves working backwards from the known structure. The
molecule to be synthesized (the target molecule) is considered to be split
into two parts (a process called disconnection). The parts are not themselves molecules, but are fragments
(called synthons) that correspond to
actual reagents. A trivial example
would be the synthesis of the target
molecule
R
1
–O–CO–R
2
This is an ester. A suitable disconnection is at the O–CO bond, giving two
synthons,
R
1
–O– and R
2
C(O)–.
The convention is to write this in the
form
R
1
–O–C(O)– R
2
⇒ R
1 –O– + R
2 –C(O)–.
Here the symbol is a logic symbol for
‘implies’; it is called the retrosynthetic arrow. In this example, suitable reagents corresponding to these
synthons would be an alcohol R
1 OH
and an acyl chloride R
2
COCl. Note
that the disconnection is always
made at a point corresponding to a
known reaction. In actual schemes,
the target molecules are complex
and a number of retrosynthetic steps
are needed.
reverberatory furnace A metallurgical furnace in which the charge
to be heated is kept separate from
the fuel. It consists of a shallow
hearth on which the charge is heated
by Ûames that pass over it and by radiation reÛected onto it from a low
roof.
reverse osmosis A method of obtaining pure water from water containing a salt, as in *desalination.
Pure water and the salt water are
separated by a semipermeable membrane and the pressure of the salt
water is raised above the osmotic
pressure, causing water from the
brine to pass through the membrane
into the pure water. This process requires a pressure of some 25 atmospheres, which makes it difÜcult to
apply on a large scale.
reversible process Any process in
which the variables that deÜne the
state of the system can be made to
change in such a way that they pass
through the same values in the reverse order when the process is reversed. It is also a condition of a
reversible process that any exchanges of energy, work, or matter
with the surroundings should be reversed in direction and order when
the process is reversed. Any process
that does not comply with these conditions when it is reversed is said to
be an irreversible process. All natural
processes are irreversible, although
some processes can be made to approach closely to a reversible process.
R F value (in chromatography) The
distance travelled by a given component divided by the distance travelled by the solvent front. For a given
system at a known temperature, it is
a characteristic of the component
and can be used to identify components.
rhe A unit of Ûuidity equal to the
reciprocal of the *poise.
rhenium Symbol Re. A silveryresorcinol
460
r
www.AzShimi.ir www.AzShimi.com