Slides4 - Chapter 4 STEROCHEMISTRY OF ALKANES AND...

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Chapter 4 STEROCHEMISTRY OF ALKANES AND CYCLOALKANES
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CONFORMATIONS OF ETHANE The different arrangements of atoms that result from rotation about a single bond are called conformations , and a specific conformation is called a conformer ( confor mational iso mer) . Conformers usually interconvert very rapidly. Sawhorse representation Newman projection View the C-C bond from an oblique angle View the C-C bond directly end-on Ethane-staggered conformation H C H H H C H H H C H H H C H H H H H H H H H H H H H H Ethane-eclipsed conformation
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CONFORMATIONS OF ETHANE In spite of the cylindrical symmetry of s bonds, there is a small 12 kJ/mol barrier to rotation due to the torsional strain (the strain due to eclipsing of bonds on neighboring atoms; slight repulsion between electron clouds of the bonds). Some conformers are more stable than others. Each CH…CH eclipsing interaction: 4 kJ/mol (1 kcal/mol = 4,18 kJ/mol) H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H 12 kJ/mol H CC H dihedral angle 0 o 60 o 120 o 180 o 240 o 360 o 300 o energie Staggered conformation Eclipsed conformation
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Slides4 - Chapter 4 STEROCHEMISTRY OF ALKANES AND...

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