Propane staggered ethane 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... 

In the eclipsed conformation of propane, we now have a larger CH3 close to H atom. This results in increased repulsive force or increased steric strain. The energy difference between the eclipsed and staggered forms of propane is greater than that of ethane. 

Conformational isomerism around the central bond in butane is more complex because file various staggered and eclipsed conformations are not equivalent as they are in ethane and propane (Figure 6.7). Starting with the eclipsed... 

All the staggered conformations of propane are equivalent to one another, and all its eclipsed conformations are equivalent to one another. The energy diagram resembles that of ethane in that it is a symmetrical one. 

As in the case of ethane, two extreme conformations of propane are possible—in one the C-H and C—C bonds are staggered in the other they are eclipsed. 

In practical evaluation of force-fields parameters the H... H and C... C non-bonded potentials were chosen first. Calculations of staggered and eclipsed rotamers of ethane, propane and n-butane then revealed the contribution of the non-bonded interactions to the total rotation barrier. For example, the van der Waals parameters proposed by Alhnger et al. in their first paper 40) on calculation of conformations were such that the repulsion between hydrogens on adjacent carbon atoms accounted for about 31% of the barrier in ethane. The remainder was accoimted for as a quantity which was added by considering the torsion interaction to be zero for all... 

The energy diagram of propane (Figure 4.9) is very similar to that of ethane, except that the torsional strain is 14 kJ/mol rather than 12 kj/mol. Once again, notice that all staggered conformations are degenerate, as are all eclipsed conformations. 

The difference in energy between staggered and eclipsed conformations of ethane is referred to as torsional strain. The torsional strain for propane is larger than that of ethane. 

---