Gauche conformation steric strain

Gauche conformation (Section 3.7) The conformation of butane in which the two methyl groups lie 60° apart as viewed in a Newman projection. This conformation has 3.8 kj/mol steric strain. 

Gasoline, manufacture of, 99-100 octane number of, 100 Gatterman-Koch reaction. 596 Gauche conformation, 95 butane and, 95-96 steric strain in, 96... 

It follows from the above X-ray data that betaines I and II have some structural peculiarities. Two main peculiarities are especially pronounced for betaines I. These compounds have the sterically strained gauche-conformation of the main chain due to the intramolecular Coulomb interaction of the cationic and anionic centers and noticeable distortions of the bond lengths in it. In Section 5 we discuss how these peculiarities of the betaine structure reflect their reactivity. 

When in compound 60 R = t-Bu, the s-trans form should be sterically crowded, and an increase of the s-cis form would be expected. The IR spectra (74SA(A)1471) seem to point out that relief of steric strain is better reached by distortion toward an s-gauche conformation than by changes in the relative amount of conformers. 

Draw Newman projections for the anti and gauche conformations about the C—C bond of these compounds. What other factors, besides steric and torsional strain, influence the stability of these conformations ... 

Rotating the totally eclipsed conformation 60° to a gauche conformation releases most, but not all, of this steric strain. The gauche conformation is still 3.8 kJ (0.9 kcal) higher in energy than the most stable anti conformation. 

Gauche conformations are generally higher in energy than anti conformations because of steric strain. 

Anti conformation 1 is lower in energy than gauche conformations 3 and 5, which possess steric strain. 

The anti conformation, it has been found, is more stable (by 0.8 kcal/mole) than the gauche (Fig. 3.4). Both are free of torsional strain. But in a gauche conformation, the methyl groups are crowded together, that is, are thrown together closer than the sum of their van der Waals radii under these conditions, van der Waals forces are repulsive (Sec. 1.19) apd raise the energy of the conformation. We say that there is van der Waals repulsion (or steric repulsion) between the... 

A potential energy plot for rotation about the C2-C3 bond in butane shows unique maxima and minima. There are two kinds of staggered conformations, gauche (steric strain) and anti, and two distinct eclipsed conformations (torsional and steric strain). 

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