Dictionary of Chemistry [6th Ed.]

p-orbitals in bonding with metals;
the stabilization of low oxidation
states, including the zero state, is a
consequence of this. This also ac-
counts for its toxicity, which is due
to the binding of the CO to the iron
in haemoglobin, thereby blocking
the uptake of oxygen.

103 carbyne

c

OC CCO

OC O

CO

__

carbon monoxide

carbon dioxide

tricarbon dioxide

(carbon suboxide)

Carbon monoxide

C

O

OH

R carboxyl group

Carboxylic acid

carbon suboxideSee tricarbon
dioxide.

carbon tetrachloride See tetra-
chloromethane.

carbonyl chloride (phosgene)A
colourless gas, COCl 2 , with an odour
of freshly cut hay. It is used in or-
ganic chemistry as a chlorinating
agent, and was formerly used as a
war gas.

carbonyl compoundA compound
containing the carbonyl group >C=O.
Aldehydes, ketones, and carboxylic
acids are examples of organic car-
bonyl compounds. Inorganic car-
bonyls are complexes in which
carbon monoxide has coordinated to
a metal atom or ion, as in *nickel
carbonyl, Ni(CO) 4. See also ligand.

carbonyl group The group >C=O,
found in aldehydes, ketones, car-
boxylic acids, amides, etc., and in in-
organic carbonyl complexes (see
carbonyl compound).

carboranesCompounds similar to
the *boranes, but with one or more
boron atoms replaced by carbon
atoms.

carborundumSee silicon carbide.

carboxyhaemoglobinThe highly
stable product formed when *haemo-

globin combines with carbon monox-

ide. Carbon monoxide competes with

oxygen for haemoglobin, with which

it binds strongly: the afÜnity of

haemoglobin for carbon monoxide is

250 times greater than that for oxy-

gen. This reduces the availability of

haemoglobin for combination with

(and transport of) oxygen and ac-

counts for the toxic effects of carbon

monoxide on the respiratory system.

carboxylateAn anion formed

from a *carboxylic acid. For example,

ethanoic acid gives rise to the

ethanoate ion, CH 3 COO–.

carboxyl group The organic group

–COOH, present in *carboxylic acids.

carboxylic acidsOrganic com-

pounds containing the group –CO.OH

(the carboxyl group; i.e. a carbonyl

group attached to a hydroxyl group).

In systematic chemical nomenclature

carboxylic-acid names end in the

sufÜx -oic, e.g. ethanoic acid,

CH 3 COOH. They are generally weak

acids. Many long-chain carboxylic

acids occur naturally as esters in fats

and oils and are therefore also

known as *fatty acids. See also glyc-

erides.

A

• Information about IUPAC nomenclature

carburizeSee carbonize.

carbylamine reaction See iso-

cyanide test.

carbyneA transient species of the

type R–C≡, with three nonbonding

electrons on the carbon atom. For-