Chapter 3:Conformations of Alkanes and Cycloalkanes |
Conformational Language
An alphabetical list of key terms in the
language of conformational
analysis is provided below, linked to the more detailed descriptions
within
the chapter pages
Anti | Description given to two substitutents attached to adjacent atoms when their bonds are at 180o with respect to each other. | |
Eclipsed | A high energy conformation where the bonds on adjacent atoms are aligned with each other. | |
Staggered | A low energy conformation where the bonds on adjacent atoms bisect each other, maximising the separation. | |
Gauche | Description given to two substitutents attached to adjacent atoms when their bonds are at 60o with respect to each other. | |
Syn | Description given to two substitutents attached to adjacent atoms when their bonds are at 0o with respect to each other. | |
Conformations | Different spatial arrangments that a molecule can adopt due to rotation about sigma bonds. | |
Conformers | Contracted version of conformational isomers. | |
Rotamers | Alternative expression for conformational isomers. | |
Conformational isomers | Structures that can be interconverted by rotation about σ bonds. | |
Cycloalkane | An ring containing only C-C bonds. | |
Heteroatom | A non-carbon atom such as O,N,S etc. | |
Heterocycle | A cyclic molecule that includes a heteratom such as O,N,S etc. as part of the ring. | |
Puckered | A non-planar geometry of a cyclic structure. | |
Ring flipping | The process by which a ring changes it's conformation. | |
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). | |
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). | |
Chair | The most stable conformation for cyclohexane. | |
Boat | A high energy conformation of cyclohexane that occurs during ring flipping. | |
Strain | Energy associated with a system due to its geometry. | |
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. | |
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. | |
Steric strain | A composite of the other strains (angle, torsional, Van der Waals) within a molecule. | |
Torsional strain | Destabilisation due to the repulsion between pairs of bonds caused by the electrostatic repulsion of the electrons in the bonds. | |
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. | |
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. |
© Dr. Ian Hunt, Department of Chemistry, University of Calgary |