gained electrons. In reducing other
substances, these atoms lose elec-
trons.
reducing sugar A monosaccharide
or disaccharide sugar that can donate
electrons to other molecules and can
therefore act as a reducing agent.
The possession of a free ketone
(–CO–) or aldehyde (–CHO) group en-
ables most monosaccharides and dis-
accharides to act as reducing sugars.
Reducing sugars can be detected by
*Benedict’s test. Compare nonreduc-
ing sugar.
reductant See reducing agent.
reduction See oxidation–
reduction.
reÜnery gasSee petroleum.
reÜningThe process of purifying
substances or extracting substances
from mixtures.
reÛuxingA laboratory technique
in which a liquid is boiled in a con-
tainer attached to a condenser (reÛux
condenser), so that the liquid contin-
uouslyÛows back into the container.
It is used for carrying out reactions
over long periods in organic synthe-
sis.
reforming The conversion of
straight-chain alkanes into branched-
chain alkanes by *cracking or by
catalytic reaction. It is used in pe-
troleum reÜning to produce hydro-
carbons suitable for use in gasoline.
Benzene is also manufactured from
alkane hydrocarbons by catalytic re-
forming. Steam reforming is a
process used to convert methane
(from natural gas) into a mixture of
carbon monoxide and hydrogen,
which is used to synthesize organic
chemicals. The reaction
CH 4 + H 2 O →CO + 3H 2occurs at about 900°C using a nickel
catalyst.
refractory 1.Having a high melt-
ing point. Metal oxides, carbides, and
silicides tend to be refractory, and
are extensively used for lining fur-
naces. 2.A refractory material.regioselectivity The effect in
which certain positions in the mol-
ecule are favoured over others in a
reaction. An example is the way in
which certain groups on the benzene
ring direct further substituents to the
meta position or to the ortho and
para positions. *Markovnikoff’s rule
for electrophilic additions to alkenes
is another example.Regnault’s method A technique
for measuring gas density by evacuat-
ing and weighing a glass bulb of
known volume, admitting gas at
known pressure, and reweighing.
The determination must be carried
out at constant known temperature
and the result corrected to standard
temperature and pressure. The
method is named after the French
chemist Henri Victor Regnault
(1810–78).relative atomic mass (atomic
weight; r.a.m.) Symbol Ar. The ratio
of the average mass per atom of the
naturally occurring form of an el-
ement to 1/12 of the mass of a car-
bon–12 atom.
A- Current values for relative atomic
masses
relative density (r.d.) The ratio of
the *density of a substance to the
density of some reference substance.
For liquids or solids it is the ratio of
the density (usually at 20°C) to the
density of water (at its maximum
density). This quantity was formerly
called speciÜc gravity. Sometimes rel-
ative densities of gases are used; for
example, relative to dry air, both
gases being at s.t.p.457 relative density
r