is ionized for a given frequency it has
many applications in chemistry.resorcinol See 1,3-dihydroxyben-
zene.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 tech-
nique for planning the series of reac-
tions required to synthesize a given
molecule. It involves working back-
wards from the known structure. The
molecule to be synthesized (the tar-
get molecule) is considered to be split
into two parts (a process called dis-
connection). The parts are not them-
selves 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 disconnec-
tion 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 retrosyn-
thetic arrow. In this example, suit-
able 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 metal-
lurgical furnace in which the chargeto be heated is kept separate from
the fuel. It consists of a shallow
hearth on which the charge is heated
byÛames that pass over it and by ra-
diation reÛected onto it from a low
roof.reverse osmosis A method of ob-
taining pure water from water con-
taining a salt, as in *desalination.
Pure water and the salt water are
separated by a semipermeable mem-
brane 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 re-
quires a pressure of some 25 atmos-
pheres, 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 re-
verse order when the process is re-
versed. It is also a condition of a
reversible process that any ex-
changes of energy, work, or matter
with the surroundings should be re-
versed in direction and order when
the process is reversed. Any process
that does not comply with these con-
ditions when it is reversed is said to
be an irreversible process. All natural
processes are irreversible, although
some processes can be made to ap-
proach closely to a reversible process.
RFvalue (in chromatography) The
distance travelled by a given compo-
nent divided by the distance trav-
elled 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 compo-
nents.rheA unit ofÛuidity equal to the
reciprocal of the *poise.rheniumSymbol Re. A silvery-resorcinol 460r