lower (+2) oxidation state; e.g. chro-
mous chloride is chromium(II) chlo-
ride (CrCl 2 ).chromyl chloride (chromium oxy-
chloride)A dark red liquid, CrO 2 Cl 2 ;
r.d. 1.911; m.p. –96.5°C; b.p. 117°C. It
is evolved as a dark-red vapour on ad-
dition of concentrated sulphuric acid
to a mixture of solid potassium
dichromate and sodium chloride; it
condenses to a dark-red covalent liq-
uid, which is immediately hydrolysed
by solutions of alkalis to give the yel-
low chromate. Since bromides and
iodides do not give analogous com-
pounds this is a speciÜc test for
chloride ions. The compound is a
powerful oxidizing agent, exploding
on contact with phosphorus and in-
Ûaming sulphur and many organic
compounds.chrysotileSee serpentine.CISee colour index.CIDNP(chemically induced dynamic
nuclear polarization)A mechanism
enabling nuclear spin to inÛuence
the direction of a chemical reaction.
This can occur in certain cases, even
though the gap between energy lev-
els of nuclear spin states in a mag-
neticÜeld is very much smaller than
the dissociation energies of chemical
bonds. Two radicals, the electrons of
which have parallel spins, can only
combine if the conversion of a *trip-
let to a *singlet can take place. In a
magneticÜeld, a triplet has three
nondegenerate states called T 0 , T+,
and T–. For a triplet-to-singlet conver-
sion to take place, one electron must
precess faster than the other for a
sufÜcient time to enable a 180°phase
difference to develop. This difference
in precession can arise when the nu-
clear spin interacts with the electron
on the radical, by means of hyperÜne
coupling.cine-substitutionA type of substi-
tution reaction in which the entering
group takes a position on an atom
adjacent to the atom to which the
leaving group is attached. See also
tele-substitution.cinnabarA bright red mineral
form of mercury(II) sulphide, HgS,
crystallizing in the hexagonal sys-
tem; the principal ore of mercury. It
is deposited in veins and impregna-
tions near recent volcanic rocks and
hot springs. The chief sources in-
clude Spain, Italy, and Yugoslavia.cinnamic acid (3-phenylpropenoic
acid)A white crystalline aromatic
*carboxylic acid, C 6 H 5 CH:CHCOOH;
r.d. 1.248 (trans isomer); m.p.
135–136°C; b.p. 300°C. Esters of cin-
namic acid occur in some essential
oils.
CIP system (Cahn–Ingold–Prelog
system)A system for the unambigu-
ous description of stereoisomers used
in the R–S convention (see absolute
configuration) and in the *E–Z con-
vention. The system involves a se-
quence rule for determining a
conventional order of ligands. The
rule is that the atom bonded directly
to the chiral centre or double bond is
considered and the ligand in which
this atom has the highest proton
number takes precedence. So, for ex-
ample, I takes precedence over Cl. If
two ligands have bonding atoms with
the same proton number, then sub-
stituents are taken into account (with
the substituent of highest proton
number taking precedence). Thus,
–C 2 H 5 has a higher precedence than
–CH 3. If a double (or triple) bond oc-
curs to a substituent, then the sub-
stituent is counted twice (or three
times). An isotope of high nucleon
number takes precedence over one
of lower nucleon number. Hydrogen
always has lowest priority in this sys-chromyl chloride 126c