3,3-Dimethylbutanes, conformational

I Sight along the C2-C3 bond of 2,3-dimethylbutane, and draw a Newman projection of the most stable conformation. 

What are the relative energies of the three possible staggered conformations around the C2-C3 bond in 2,3-dimethylbutane (See Problem 3.42.)... 

The influence of the a-bond isomerism is in agreement with the slow exchange spectra of 2,3-dimethylbutane and 1,2-dimethycylohexane in solution 16,17). Taking into account the different isomeric states of the bonds in a- and P-position on both sides of the observed carbons the slow exchange spectra of CH2-chain molecules have to be explained by conformational variations in chain segments of five carbon atoms. 

From X-ray diffraction experiments28 it is known that in the crystalline phase the erythrodiisotactic poly(l,2-dimethyltetramethylene) has a (g+aaa g aaa)n structure as shown in Fig. 13. The bold printed letters in the denotation give the conformation of the CH—CH bond. In agreement with this structure and low temperature solution state spectra of 2,3-dimethylbutane, 3,4-dimethylhexane, and 4,5-dimethyloctane 29 30) in which the CHCH bond rotation is frozen the crystalline signals can be assigned conclusively. Like for the crystalline state of poly(l,2-... 

Problem 4.9 Draw a graph of potential energy plotted against angle of rotation for conformations of (a) 2.. l-dimethylbutane. (h) 2-methylbutane. Point out the factors responsible for energy differences. -4... 

The conformation of l-substituted-3,3-dimethylbutanes seems to depend in part on a,. Thus, AEX for the equilibrium between gauche, 4, and trans, 5, conformers, determined by Whitesides, Sevenair, and Goetz,31) have been correlated with the equation 32)... 

Show all of the staggered conformers of 2,3-dimethylbutane and estimate the energy differences between them. 

The two conformers of 2,3-dimethylbutane (10) are of nearly equal energy despite the... 

Draw a Newman projection of the highest-energy conformation of 2,3-dimethylbutane about the C2—C3 bond. 

Draw an energy versus dihedral angle plot for the conformations of 2,3-dimethylbutane about the C-2—C-3 bond. 

This conformation of 2,3-dimethylbutane is the most stable because it is staggered and has the fewest CH3-CH3 gauche interactions. 

Aryl-2-chloro-2,3-dimethylbutanes form both benzylic and equilibrating ions upon ionization. The benzylic ions are destabilized due to severe steric crowding in the planar conformation necessary for optimal charge delocalization. 

The conformation isomerism in a wide range (31 examples) of 1-sub-stituted derivatives of 3,3-dimethylbutane has been examined. In some cases, the temperature variation of the vicinal coupling constants was studied. In 1,1,2-trichloroethane the coupling constants of the gauche and anti isomers are deduced from solvent-dependent changes in the observed coupling constants. In some similar systems (1,1,2-trichloro- and 1,1,2-tribromoethane in carbon tetrachloride and in benzene), a correlation of the dipole moments of the compounds and the vicinal coupling constants was found.Rotational isomerism in the phenylalanine anion and dipolar ion has been studied in deuterium oxide solutions. 

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