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| Anti |
Description given to
two substitutents attached to adjacent atoms when
their bonds are at 180o with respect to each other. |
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| Eclipsed |
A high energy
conformation where the bonds on adjacent atoms are aligned
with each other. |
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| Staggered |
A low energy
conformation where the bonds on adjacent atoms bisect
each other, maximising the separation. |
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| Gauche |
Description given to
two substitutents attached to adjacent atoms when
their bonds are at 60o with respect to each other. |
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| Syn |
Description given to
two substitutents attached to adjacent atoms when
their bonds are at 0o with respect to each other. |
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| Conformations |
Different spatial
arrangments that a molecule can adopt due to rotation
about sigma bonds. |
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| Conformers |
Contracted version
of conformational isomers. |
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| Rotamers |
Alternative
expression for conformational isomers. |
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| Conformational
isomers |
Structures that can
be interconverted by rotation about σ
bonds. |
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| Cycloalkane |
An ring containing
only C-C bonds. |
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| Heteroatom |
A non-carbon atom
such as O,N,S etc. |
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| Heterocycle |
A cyclic molecule
that includes a heteratom such as O,N,S etc.
as part of the ring. |
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| Puckered |
A non-planar
geometry of a cyclic structure. |
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| Ring flipping |
The process by which
a ring changes it's conformation. |
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| Axial |
A position on a
chair cyclohexane in which the bond to the ring is
perpendicular to the average plane of the ring (i.e. pointing
towards
the poles). |
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| Equatorial |
A position on a
chair cyclohexane in which the bond to the ring is
approximately in the average plane of the ring (i.e. around the
equator). |
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| Chair |
The most stable
conformation for cyclohexane. |
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| Boat |
A high energy
conformation of cyclohexane that occurs during ring flipping. |
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| Strain |
Energy associated
with a system due to its geometry. |
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| Angle
strain |
Destabilisation due
to distortion of a bond angle from its optimum
value caused by the electrostatic repulsion of the electrons in the
bonds. |
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| Van der Waals
strain |
Destabilisation due
to the repulsion between the electron clouds of
atoms or groups. Also known as Van der Waals repulsion. This occurs
when
atoms or groups are too close to each other due to the electrostatic
repulsion
of the electrons. |
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| Steric strain |
A composite of the
other strains (angle, torsional, Van der Waals)
within a molecule. |
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| Torsional
strain |
Destabilisation due
to the repulsion between pairs of bonds caused
by the electrostatic repulsion of the electrons in the bonds. |
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| Torsional
angle |
Angle between C-X
and C-Y bonds in a X-C-C-Y system when viewed along
the C-C bond. Rotation about the C-C bond will change this torsional
angle.
This is also known as a dihedral angle. |
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| Ring strain |
The destabilisation
of a cyclic structure compared to a related non-cyclic
structure, mainly due to angle and torsional strain. This extra energy
is released when the ring is broken. |
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