Dictionary of Chemistry [6th Ed.]

animal charcoal See charcoal.

animal starch See glycogen.

anionA negatively charged *ion,

i.e. an ion that is attracted to the

*anode in *electrolysis. Compare

cation.

anionic detergentSee detergent.

anionic resin See ion exchange.

anisotropic Denoting a medium in

which certain physical properties are

different in different directions.

Wood, for instance, is an anisotropic

material: its strength along the grain

differs from that perpendicular to

the grain. Single crystals that are not

cubic are anisotropic with respect to

some physical properties, such as the

transmission of electromagnetic radi-

ation. Compare isotropic.

annealingA form of heat treat-

ment applied to a metal to soften it,

relieve internal stresses and instabili-

ties, and make it easier to work or

machine. It consists of heating the

metal to a speciÜed temperature for a

speciÜed time, both of which depend

on the metal involved, and then al-

lowing it to cool slowly. It is applied

to both ferrous and nonferrous met-

als and a similar process can be ap-

plied to other materials, such as

glass.

annelationSee annulation.

annulationA type of chemical re-

action in which a ring is fused to a

molecule by formation of two new

bonds. Sometimes the term annela-

tionis used. See also cyclization.

annulenesOrganic hydrocarbons

that have molecules containing sim-

ple single rings of carbon atoms

animal charcoal 38

a

[14]-Annulene

[18]-Annulene

H

[30]-Annulene

H

HH

H H

HH

HH

HH

H H

HH

H

H H

H

H

H

H

H H

H

H

H

HH

HH

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H H

HH

H

H

H

H

HH

H

HH

Annulenes