Conformational analysis propane

Conformational analysis is the study of the energetics of different conformations. Many reactions depend on a molecule s ability to twist into a particular conformation conformational analysis can help to predict which conformations are favored and which reactions are more likely to take place. We will apply conformational analysis to propane and butane first, and later to some interesting cycloalkanes. 

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... 

An energy diagram showing the conformational analysis of propane. 

Conformational analysis of butane is a bit more complex than the conformational analysis of either ethane or propane. Look carefully at the shape of the energy diagram for butane (Figure 4.11), and then we will analyze it step by step. 

Exciton coupling between the two styryl chromophores in each of the conformers (A)-(C) leads to a negative Cotton effect at around 270 nm, as shown by theoretical analysis using the 71-electron SCF Cl dipole velocity MO method. Therefore, the tram-2,.1-disubstituted spirocyclo-propane-1,9 -fluorene derivative 6, from which the distyryl derivative was obtained, must have accordingly the 2S3S absolute configuration122. 

An analysis of the conformational profiles of propanal, chloroethanal and 2-chloro-propanal58 reveals two noteworthy trends ... 

Butane provides a more complex example. Here there are two different types of carbon-carbon bonds. Analysis of the conformations available by rotation about the bond between carbon 1 and carbon 2 (or carbon 3 and carbon 4) is very similar to the analysis of propane, with the difference that there is an ethyl group on one carbon rather... 

The preferred conformations of carbonyl compounds, like 1-alkenes, are eclipsed rather than bisected, as shown below for ethanal and propanal. The barrier for methyl group rotation in ethanal is 1.17kcal/mol. Detailed analysis has indicated that small adjustments in molecular geometry, including a-bond lengthening, must be taken into account to quantitatively analyze the barrier. The total barrier can be dissected into nuclear-nuclear, electron-electron, nuclear-electron, and kinetic energy (At), as described in Topic 1.3 for ethane. MP2/6-311+G (Mf,2p) calculations lead to the contributions tabulated below. The total barrier found by this computational approach is very close to the experimental value. Contributions to the ethanal energy barrier in kcal/mol are shown below. 

Biirgi H-B, Houshell WD, Nachbar RB Jr, Mislow K (1983) Conformational dynamics of propane, di-tert-butylmethane, and bis(9-triptycyl)methane. An analysis of the symmetry of two threefold rotors on a rigid frame in terms of nonrigid molecular structure and energy hypersurfaces. J Am Chem Soc 105 1427-1438... 

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