Information AboutChemical Conformation |
| CATEGORIES ABOUT CONFORMATIONAL ISOMERISM | |
| stereochemistry | |
| physical organic chemistry | |
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The population of different conformers follows a Boltzmann Distribution : : The subscript i and j represent the highest and lowest energy. g is the number of conformations found at that particular energy, the degeneracy. N is the population of molecules in a particular conformation. Two important forms of conformational isomerism exist in Linear Alkane Conformation s with staggered, eclipsed and gauche conformers and Cyclohexane Conformation s with chair and boat conformers. Another example of conformational isomerism is Protein Folding , where some shapes are stable and functional, but others are not. Conformational isomerism is also found in Atropisomer s. CONSEQUENCES If the Eclipsed conformations of an Isomer have high enough potentials, they may prevent rotation of Substituent s to different Staggered conformations at sufficiently low energy levels. This will result in a Racemic mixture of conformations that may or may not have different Reactivities in situations such as Enzymatic reactions in which molecular shape is usually a key factor of operation. CONFORMER DEPENDENT REACTIONS The E2 Elimination Mechanism relies on the base or acid attacked substituent being in an Antiperiplanar configuration along a bond with respect to the Leaving Group . This prerequisite for reaction is important in understanding organic elimination reaction pathways, especially those involving halogenated cyclic alkanes such as Cyclohexane s. Two adjacent Substituent s on a cyclic alkane can only undergo an E2 elimination if they are both axial to the ring and hence antiperiplanar. A combination of axial and equatorial substituents cannot react through an E2 mechanism, though ring flips (with associated reconformation) may allow reactions to occur if they are not precluded by an energy barrier or Steric Lock through isopropyl or larger substituents. CONDITIONS Conformational isomerism only occurs around single bonds as a result of the requirement of breaking one or more Pi Bond s to rotate Substituent s about a Sigma Bond axis in double and triple bonded atoms. Conformers sufficiently constrained to exhibit measurable isomerism are unique from various flavours of stereoisomers in the fact that changes in stereochemistry are independent from any mechanism and instead rely only on molecular energy. SEE ALSO |
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