Structure and nonbonded repulsions

The analysis of the results concentrated on the time-averaged structure and on correlation functions that illustrate the time-dependence of internal motions. A key conclusion was that the internal motion was fluidlike at ordinary temperatures, i.e. that the dynamics of atomic displacements are dominated by collisions with neighboring atoms, at least on the picosecond time scale. Hence, it is argued, ...many of the dynamical properties (though not necessarily the correct average structure) can be obtained from any potential function which includes the forces that depend strongly upon distance (covalent and hydrogen bonds, nonbonded repulsions) and provides sufficient attractive interactions to preserve the compact structure of the native system. ... 

The enamines derived from cyclohexanones are of particular interest. The pyrrolidine enamine is most frequently used for synthetic applications. The enamine mixture formed from pyrrolidine and 2-methylcyclohexanone is predominantly isomer 17.106 A steric effect is responsible for this preference. Conjugation between the nitrogen atom and the tt orbitals of the double bond favors coplanarity of the bonds that are darkened in the structures. In isomer 17 the methyl group adopts a quasi-axial conformation to avoid steric interaction with the amine substituents.107 A serious nonbonded repulsion (A1,3 strain) in 18 destabilizes this isomer. 

Since there are two covalent bonds (each accounting for 2(35) and one nonbonded repulsive interaction (—(35) in this VB structure, its energy simply expresses a balance between the two corresponding energy quantities, namely ... 

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