Dictionary of Chemistry [6th Ed.]

anthocyaninOne of a group of

*Ûavonoid pigments. Anthocyanins

occur in various plant organs and are

responsible for many of the blue,

red, and purple colours in plants

(particularly inÛowers).

anthraceneA white crystalline

solid, C 14 H 10 ; r.d. 1.28; m.p. 215.8°C;

b.p. 341.4°C. It is an aromatic hydro-

carbon with three fused rings (see

formula), and is obtained by the dis-

tillation of crude oils. The main use

is in the manufacture of dyes.

anthocyanin 40

a

O

O

1

2

3

5 4

6

7

8

Anthraquinone

anthraciteSee coal.

anthraquinoneA colourless crys-

talling *quinone; m.p. 154°C. It may

be prepared by reacting benzene

with phthalic anhydride. The com-

pound is the basis of a range of

dyestuffs. *Alizarin is an example.

anti 1.See torsion angle. 2.See

e–z convention.

antiaromatic See pseudoaromatic.

antibioticsSubstances that destroy

or inhibit the growth of microorgan-

isms, particularly disease-producing

bacteria. Antibiotics are obtained

from microorganisms (especially

moulds) or synthesized. Common

antibiotics include the penicillins,

streptomycin, and the tetracyclines.

They are used to treat various infec-

tions but tend to weaken the body’s

natural defence mechanisms and can

cause allergies. Overuse of antibiotics

can lead to the development of resis-

tant strains of microorganisms.

antibonding orbitalSee orbital.

anticlinalSee torsion angle.

antiferromagnetism See magnet-

ism.

antiÛuorite structure A crystal

structure for ionic compounds of the

type M 2 X, which is the same as the

Ûuorite (CaF 2 ) structure except that

the positions of the anions and

cations are reversed, i.e. the cations

occupy the F–sites and the anions oc-

cupy the Ca2+sites. Examples of the

antiÛuorite structure are given by

K 2 O and K 2 S. See fluorite structure.

antifoaming agentA substance

that prevents a foam from forming,

employed in such processes as elec-

troplating and paper-making, and in

water for boilers. They are com-

pounds that are absorbed strongly by

the liquid (usually water) but lack the

properties that allow foaming. Sub-

stances used include polyamides,

polysiloxanes and silicones.

antifreeze A substance added to

the liquid (usually water) in the cool-

ing systems of internal-combustion

Anthracene

O

R

R

R

R

R

R

R

Anthocyanin