An Introduction to Environmental Chemistry

7.5 Further reading

Cox, R.A., Hewitt, C.N., Liss, P.S., Lovelock, J.E., Shine, K.R. & Thrush, B.A. (eds) (1997)

Atmospheric chemistry of sulphur in relation to aerosols, clouds and climate. Philosoph-

ical Transactions of the Royal Society of London352B, 139–254.

IPCC (2001) Climate Change 2001: The Scientific Basis. Contribution of Working Group

I to the Third Assessment Report, Intergovernmental Panel on Climate Change. Cambridge

University Press, Cambridge.

Jones, K.C and De Voogt, P. (1999) Persistent organic pollutants (POPs): state of the

science. Environmental Pollution 100 , 209–221.

Schimel, D.S. & Wigley, T.M.L. (eds) (2000) The Carbon Cycle. Cambridge University

Press, Cambridge.

Turner, B.L., Clark, W.C., Kates, R.W., Richards, J.F., Mathews, J.T. & Meyer, W.B. (eds)

(1990) The Earth as Transformed by Human Action.Cambridge University Press,

Cambridge.

7.6 Internet search keywords

Global Change 281

valuable therapeutic drug (a sedative) while

the other enantiomer is highly toxic. Between

1957 and 1960 thalidomide was prescribed in

at least 46 countries to alleviate morning

sickness associated with pregnancy. As a

consequence of the two enantiomers being

present thousands of babies were born with

birth defects.

Fig. 2Assignment of ‘R’ and ‘S’ to the enantiomers

of a molecule comprising a central carbon atom

(central circle) to which –CH 3 , –H, –Br, –COOH

groups are attached.

route from the highest priority group to the
second highest priority group lies in a
clockwise or anticlockwise direction.
Clockwise is assigned ‘R’ (from the Latin
rectus, right) while anticlockwise is assigned
‘S’ (from the Latin sinister, left). In the chiral
molecule we began with (Fig. 1), prioritizing
the groups yields the order –Br>-COOH>
-CH 3 >-H. Figure 2 shows the assignment of
‘R’ and ‘S’ to the enantiomers. In this figure,
as in Fig. 1, the wedge bonds rise from the
plane of the page toward the viewer; and
the dashed bond recedes from the plane of
the page away from the viewer.
A mixture containing equal proportions of
two enantiomers is termed a racemic mixture
and is indicated by the prefix ‘RS-’. During
organic synthesis it is usual for a chiral
product to be produced as an RS mixture
(unless the reaction has been tailored to
produce a specific chiral product). Chirality is
important because it affects a molecule’s
activity. For example, the compound
thalidomide has one enantiomer that is a

Mirror

Br

COOH CH 3

H

Anticlockwise

́S ́

Br

CH 3 COOH

H

Clockwise

́R ́

IGBP

global carbon cycle

past global changes

CO 2 Mauna Loa

atmospheric CO 2

CO 2 ice cores

CO 2 biosphere

CO 2 O 2 seasonality

CO 2 fossil fuel burning

CO 2 deforestation