Biology Reference
In-Depth Information
120
PRECISE DEFINITION OF THE
ANGLE
To define the angle precisely, look down the bond (Fig. 5-4). Hold
the atom fixed, together with C, H and the R-group. Rotate the N, H and
C
-1
, atoms counter-clockwise. That defined the angle. Unfortunately, there
are two conventions. The old one used in some textbooks (see, for example,
Dickerson and Geis, 1969) defines the angle as 0
0
in the flat extended
configuration. The new one accepted by current literatures defines angle
as -180° in the same configuration.
Figure 5-4
. Definition of the angle.
