lower (+2) oxidation state; e.g. chromous chloride is chromium(II) chloride (CrCl 2 ).
chromyl chloride (chromium oxychloride) 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 addition of concentrated sulphuric acid
to a mixture of solid potassium
dichromate and sodium chloride; it
condenses to a dark-red covalent liquid, which is immediately hydrolysed
by solutions of alkalis to give the yellow chromate. Since bromides and
iodides do not give analogous compounds this is a speciÜc test for
chloride ions. The compound is a
powerful oxidizing agent, exploding
on contact with phosphorus and inÛaming sulphur and many organic
compounds.
chrysotile See serpentine.
CI See 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 levels of nuclear spin states in a magnetic Üeld 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 *triplet to a *singlet can take place. In a
magnetic Üeld, a triplet has three
nondegenerate states called T 0 , T + ,
and T – . For a triplet-to-singlet conversion 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 nuclear spin interacts with the electron
on the radical, by means of hyperÜne
coupling.
cine-substitution A type of substitution 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.
cinnabar A bright red mineral
form of mercury(II) sulphide, HgS,
crystallizing in the hexagonal system; the principal ore of mercury. It
is deposited in veins and impregnations near recent volcanic rocks and
hot springs. The chief sources include 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 cinnamic acid occur in some essential
oils.
CIP system (Cahn–Ingold–Prelog
system) A system for the unambiguous description of stereoisomers used
in the R–S convention (see absolute
configuration) and in the *E–Z convention. The system involves a sequence 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 example, I takes precedence over Cl. If
two ligands have bonding atoms with
the same proton number, then substituents 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 occurs to a substituent, then the substituent 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 syschromyl chloride
126
c
www.AzShimi.ir www.AzShimi.com
chromyl chloride (chromium oxychloride) 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 addition of concentrated sulphuric acid
to a mixture of solid potassium
dichromate and sodium chloride; it
condenses to a dark-red covalent liquid, which is immediately hydrolysed
by solutions of alkalis to give the yellow chromate. Since bromides and
iodides do not give analogous compounds this is a speciÜc test for
chloride ions. The compound is a
powerful oxidizing agent, exploding
on contact with phosphorus and inÛaming sulphur and many organic
compounds.
chrysotile See serpentine.
CI See 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 levels of nuclear spin states in a magnetic Üeld 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 *triplet to a *singlet can take place. In a
magnetic Üeld, a triplet has three
nondegenerate states called T 0 , T + ,
and T – . For a triplet-to-singlet conversion 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 nuclear spin interacts with the electron
on the radical, by means of hyperÜne
coupling.
cine-substitution A type of substitution 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.
cinnabar A bright red mineral
form of mercury(II) sulphide, HgS,
crystallizing in the hexagonal system; the principal ore of mercury. It
is deposited in veins and impregnations near recent volcanic rocks and
hot springs. The chief sources include 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 cinnamic acid occur in some essential
oils.
CIP system (Cahn–Ingold–Prelog
system) A system for the unambiguous description of stereoisomers used
in the R–S convention (see absolute
configuration) and in the *E–Z convention. The system involves a sequence 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 example, I takes precedence over Cl. If
two ligands have bonding atoms with
the same proton number, then substituents 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 occurs to a substituent, then the substituent 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 syschromyl chloride
126
c
www.AzShimi.ir www.AzShimi.com