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1,3-diaxial interactions
Steric hindrance between an axial substituent on a chair conformation and the hydrogens on ring positions three carbons away.
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Angle strain
The formation of bent σ bonds in rings (3-, 4-membered) to accommodate unnatural ring angles.
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A-value
Energetic cost of putting a substituent group in the axial position of a cyclohexane Chair as opposed to the equatorial position.
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Axial
Bond positions on the cyclohexane chair parallel to the central rotation axis. These are typically drawn as vertical lines branching from the chair structure.
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Bicyclic
A compound that contains two rings which share atoms with each other.
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Bredt's Rule
No bridgehead alkenes. Bridgehead carbons are too constrained in the ring structures to incorporate double bonds.
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Bridged
Joining of rings with more than two atoms. These shared atoms constitute a bridge.
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Bridgehead carbons
Points at which rings meet in bridged polycyclic hydrocarbons.
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Boat
Less stable conformation of cyclohexane; resembles a boat.
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Chair
The most stable conformation of cyclohexane; resembles a lawn chair.
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Chair flip
Interconversion between two chair conformations.
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Equatorial
Bond positions on the cyclohexane chair that lie sideways toward the equatorial plane of the chair.
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Flagpole hydrogen
Hydrogens at two ends of the cyclohexane boat conformation that repel each other due to steric hindrance.
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Fused
The joining of rings that share two atoms and the bond between them.
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Heat of Formation
The energy change that occurs when a molecule is assembled from its component atoms.
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Polycyclic
Compound that contains several rings joined with common atoms.
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Ring strain
Unfavorable energetics that arise from ring formation. These include both angle strain and torsional strain.
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Spiro
Ring joining that shares a single atom, creating rings that lie in perpendicular planes.
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Steric hindrance
Repulsion between the electron clouds on bulky groups of a molecule or between molecules.
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Torsional strain
Resistance to rotation about a single bond caused by steric hindrance of eclipsing interactions.
