Search results
Results from the WOW.Com Content Network
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 .
More specific examples of conformations are detailed elsewhere: Ring conformation Cyclohexane conformations, including with chair and boat conformations among others. Cycloalkane conformations, including medium rings and macrocycles; Carbohydrate conformation, which includes cyclohexane conformations as well as other details.
In the most stable chair form of cyclohexane, axial hydrogens on adjacent carbon atoms are pointed in opposite directions, virtually eliminating eclipsing strain. In medium-sized rings (7 to 13 carbon atoms) conformations in which the angle strain is minimised create transannular strain or Pitzer strain .
For example, in the conformation of (Z)-4-methylpent-2-ene, the molecule isn't frozen in the favored conformer but rotates in the dihedral angle around 30° at <1kcal/mol cost. In stereoselective reactions, there are 2 effects of allylic strain on the reaction which is the sterics effect and the electronic effects.
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).
However, in some cases, the isolation of individual conformers of substituted cyclohexane derivatives has been achieved at low temperatures (–150 °C). Most compounds with nonplanar rings engage in degenerate ring flipping. One well-studied example is titanocene pentasulfide, where the inversion barrier is high relative to cyclohexane's.