Ethane eclipsed conformation

Figure 3.55 Leading cjch-och hyperconjugative donor-acceptor interactions in the staggered (left) and eclipsed (right) conformers of ethane.

Fig.I. Newman projections of the staggered (I) and eclipsed (II) conformations of ethane.

Ethane conformations. The eclipsed conformation has a dihedral angle 0 = 0° and the staggered conformation has 0 = 60°. Any other conformation is called a skew conformation. 

Conformation and Conformational Analysis Conformation of Ethane Conformation of Propane Conformation of Butane Eclipsed and Staggered Eorms Ring Strains in Cycloalkanes Principles of Conformation 165... 

Rotating the atoms on one carbon by 60° converts an eclipsed conformation into a staggered conformation, and vice versa. These conformations are often viewed end-on— that is, looking directly down the carbon-carbon bond. The angle that separates a bond on one atom from a bond on an adjacent atom is called a dihedral angle. For ethane in the staggered conformation, the dihedral angle for the C-H bonds is 60°. For eclipsed ethane, it is 0°. 

If compounds are stereoisomers, we can make a further distinction as to isomer type. If single-bond rotation easily interconverts the two stereoisomers (as with staggered and eclipsed ethane), we call them conformers. If the two stereoisomers can be interconverted only by breaking and remaking bonds (as with cis- and from-1,2-dimethylcyclopentane), we call them configurational isomers. ... 

Thus, even a one-CW theory of ethane conformational isomerism would predict that staggered is more stable than eclipsed ethane, if overlap were included in the analysis (vide infra). 

Eclipsed ethane (Section 2.5) The conformation of ethane in which all carbon-hydrogen bonds are as close as possible. This conformation is not an energy minimum, but the top of the barrier separating two molecules of the stable, staggered conformation of ethane. 

The data of Table 2.1 on the calculations of total energies for ethane in the stable D3d and the eclipsed D31, conformations as well as for its hypothetical bridged structural isomers with D2h and 04 symmetry may give an idea of how the results of nonempirical calculations are refined with the gradual extension of the basis set. 

Figure 1 Ethane internal rotation showing equilibrium (staggered, S) and barrier top (eclipsed, E) conformers...

Acetaldehyde is more stable in the eclipsed conformation (rH-c-c=o = 9°, Scheme 7) and this preference is well reproduced by ab initio MO calculations, as well as by the molecular mechanics (MM2) approach. The higher energy of the bisecting conformation has been ascribed to repulsive overlap between the C-H bond orbitals, i.e the same origin as that for eclipsed ethane. 

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