(376bp) Energy Profiles of the Ring Puckering of Cyclopentane, Methylcyclopentane and Ethylcyclopentane

The use of pseudoangles to describe five-membered ring puckering has been well established and widely used, particularly for studying ribose conformations. Several studies have investigated the relative energy of a given molecule as a function of the pseudoangle. However, most of these studies focused on a particular minimum. However, for molecules that have multiple exocyclic torsion angles along the ring (e.g. ribose) or an extended exocyclic group, a molecule can have multiple pseudoangle energetic profiles. Ethylcyclopentane is the simplest example of this, with the ethyl group adopting (+/-)-gauche and trans conformation relative to the ring. Interestingly, there has not been any experimental or computational investigations on ethylcyclopentane's ring puckering.

Herein we report all of the minima of ethylcyclopentane and its two pseudoangle rotational profiles as determined using electron correlated theories. The puckering conformations and relative energies for cyclopentane and methylcyclopentane are also reported, allowing us to investigate the influence that exocyclic methyl and ethyl groups have on the ring pucker within a uniform theoretical framework. Geometry optimizations were performed using MP2 and cc-pVTZ and aug-cc-pVTZ basis sets, with relative potential energies (rPE) computed at MP2.5 and CCSD(T) theory levels. The pseudoangle rotational profiles were computed at MP2.5/cc-pVTZ//HF/6-31G(d).