example, the ground electronic configuration of the
oxygen molecule (O 2 ) is
1 σg^2 , 1 σu^2 , 2 σg^2 , 2 σu^2 , 1 πu^4 , 3 σg^2 , 1 πg^2resulting in the
(^3) Σg, (^1) ∆g, and (^3) Σg+multiplets
configuration (molecular) In the context of stereo-
chemistry, the term is restricted to the arrangements of
atoms of a MOLECULAR ENTITY in space that distin-
guishes stereoisomers, the isomerism of which is not
due to conformational differences.
conformation The spatial arrangements of atoms
affording distinction between STEREOISOMERSthat can
be interconverted by rotations about formally single
bonds. One of the possible spatial orientations of a sin-
gle molecule.
congener A substance literally con- (with) generated
or synthesized by essentially the same synthetic chemi-
cal reactions and the same procedures. ANALOGs are
substances that are analogous in some respect to the
prototype agent in chemical structure.
Clearly congeners may be analogs or vice versa,
but not necessarily. The term congener,while most
often a synonym for HOMOLOGUE, has become some-
what more diffuse in meaning so that the terms con-
generand analogare frequently used interchangeably
in the literature.
conjugate acid-base pair The BRONSTED ACIDBH+,
formed on protonation of a base B, is called the conju-
gate acid of B, and B is the conjugate base of BH+. (The
conjugate acid always carries one unit of positive
charge more than the base, but the absolute charges of
the species are immaterial to the definition.) For exam-
ple, the Bronsted acid HCl and its conjugate base Cl–
constitute a conjugate acid-base pair.
conjugated double bonds Double bonds that are
separated from each other by one single bond such as
CH 2 CH–CHCH 2.
conjugated system(conjugation) In the original
meaning, a conjugated system is a molecular entity
whose structure can be represented as a system of alter-
nating single and multiple bonds, e.g.,
CH 2 CHCHCH 2 CH 2 CH–CN
In such systems, conjugation is the interaction of one p-
orbital with another across an intervening sigma bond
in such structures. (In appropriate molecular entities, d-
orbitals may be involved.) The term is also extended to
the analogous interaction involving a p-orbital contain-
ing an unshared electron pair, e.g.,
:Cl–CHCH 2
See also DELOCALIZATION; HOMOCONJUGATION;
RESONANCE.
conjugative mechanism SeeELECTRONIC EFFECT.
connectivity In a chemical context, the information
content of a line formula, but omitting any indication
of BONDmultiplicity.
conrotatory SeeELECTROCYCLIC REACTION.
consensus sequence A SEQUENCE of DNA, RNA,
protein, or carbohydrate derived from a number of
similar molecules that comprises the essential features
for a particular function.
constitution The description of the identity and con-
nectivity (and corresponding bond multiplicities) of the
58 configuration (molecular)
A conjugated structure has alternate single and double bonds
between carbon atoms in an organic compound.