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A monosubstituted cyclohexane is one in which there is one non-hydrogen substituent in the cyclohexane ring. The most energetically favorable conformation for a monosubstituted cyclohexane is the chair conformation with the non-hydrogen substituent in the equatorial position because it prevents high steric strain from 1,3 diaxial interactions. [11]
A-values help predict the conformation of cyclohexane rings. The most stable conformation will be the one which has the substituent or substituents equatorial. When multiple substituents are taken into consideration, the conformation where the substituent with the largest A-value is equatorial is favored.
Another conformation of cyclohexane exists, known as boat conformation, but it interconverts to the slightly more stable chair formation. If cyclohexane is mono-substituted with a large substituent , then the substituent will most likely be found attached in an equatorial position, as this is the slightly more stable conformation .
Macrocycles can access a number of stable conformations, with preference to reside in conformations that minimize transannular nonbonded interactions within the ring (e.g., with the chair and chair-boat being more stable than the boat-boat conformation for cyclooctane, because of the interactions depicted by the arcs shown).
The cis isomer is already in the correct geometry in its most stable conformation; therefore, it eliminates easily. The repulsion between an axial t -butyl group and hydrogen atoms in the 1,3-diaxial position is so strong that the cyclohexane ring will revert to a twisted boat conformation.
A is thus the most stable conformation &, of all the other conformations, occurs most often in room temperature. Valleys A & B are local energy minima & A is global minima. A & B can thus be classified as conformers.
In addition, cyclohexane conformations can be used to indicate if the molecule has any 1,3 diaxial-interactions which are steric interactions between axial substituents on the 1,3, and 5 carbons. [8] Chair conformation of beta-D-Glucose The cyclohexane conformations in relation to the potential energy at each conformation
The chair conformation minimizes both angle strain and torsional strain by having all carbon-carbon bonds at 110.9° and all hydrogens staggered from one another. [2] The conformational changes that occur in a cyclohexane ring flip take place over several stages. Structure D (10.8 kcal/mol) is the highest energy transition state of the process.