linked to the quantum mechanical concept of “reso-
nance energy.” The term resonanceis also used to refer
to the DELOCALIZATIONphenomenon itself.
See alsoMESOMERISM.
resonance effect This is the term most commonly
used to describe the influence (on reactivity, spectra,
etc.) of a SUBSTITUENTthrough electron DELOCALIZA-
TIONinto or from the substituent. The use of the term
obviates the need to attempt to distinguish between the
operation of the MESOMERIC EFFECT and the ELEC-
TROMERIC EFFECT. (An alternative term with essentially
the same meaning is conjugative effect.At one time
“tautomeric effect” was also used, but it was aban-
doned because TAUTOMERISMimplies reorganization of
the atomic nuclei.) The effect is symbolized by R.
resonance energy The difference in potential energy
between the actual MOLECULAR ENTITYand the CON-
TRIBUTING STRUCTUREof lowest potential energy. The
resonance energy cannot be measured, but only esti-
mated, since contributing structures are not observable
MOLECULAR ENTITIES.
See alsoRESONANCE.
resonance Raman spectroscopy A spectroscopic
technique increasingly used in bioinorganic chemistry
for characterization and assignment of vibrations
directly connected with a CHROMOPHORE, as well as
for the assignment of the chromophore. The excitation
frequency is applied close to the absorption maximum
of the chromophore. Particularly useful for deeply col-
ored species.
See alsoRAMAN SPECTROSCOPY.
respiration The process where mitochondria in the
cells of plants and animals release chemical energy
from sugar and other organic molecules through chem-
ical oxidation.
See alsoKREBS CYCLE.
resting potential The state of a neuron’s charge—the
gradient of electric potential across the membrane—
when it is in a resting state and ready to receive a nerve
impulse (the action potential); usually consists of a neg-
ative charge on the inside of the cell relative to the out-
side. At rest, the cell membrane electrical gradient
maintains a negative interior charge of –70 mV.restriction enzyme(restriction endonuclease) A
DNA-cutting protein that recognizes a specific
nucleotide sequence in a DNA molecule and excises
the DNA; found in bacteria. Some sites are common
and occur every several hundred base pairs, while oth-
ers are less common. Bacteria possess several hundred
restriction enzymes that cut more than 100 different
DNA sequences. Each restriction enzyme has a single,
specific recognition sequence and cuts the DNA
molecule at a specific site. Some restriction enzymes
have been used in recombinant DNA technology.retroaddition SeeCYCLOELIMINATION.retrocycloaddition SeeCYCLOELIMINATION.retro-ene reaction SeeENE REACTION.reverse micelle(reversed micelle) See INVERTED
MICELLE.reverse osmosis During osmosis, water flows from
a less-concentrated solution through a semipermeable
membrane to a more-concentrated saline solution
until concentrations on both sides of the membrane
are equal. Reverse osmosis forces molecules to flow
through a semipermeable membrane from the concen-
trated solution into a diluted solution using greater
hydrostatic pressure on the concentrated-solution
side.
See alsoOSMOSIS.reversible reaction A CHEMICAL REACTION that
can occur in both directions, either OXIDATIONor
REDUCTION.reversible reaction 237