Ch_322a_4.011

Ch_322a_4.011 - Sigma Bonds and Bond Rotation Rotation is...

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Sigma Bonds and Bond Rotation Rotation is possible around single bonds (sigma bonds). The orientations of atoms and groups that result from rotation are called conformations . Different conformations may have different energies. An analysis of the energy changes with rotation around a bond is called conformational analysis . Conformational Analysis of Ethane: H 3 C-CH 3 An energy barrier of close to 3.0 kcal/mol is observed during rotation around the C-C bond in ethane. This energy barrier is attributed to torsional strain . C C H H H H H H
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The Conformations of Ethane An analysis of the rotation around the C-C bond in ethane shows there are two extreme conformations . These two conformations called eclipsed and staggered are shown below. These two conformations interconvert by simple rotation around the C-C bond. eclipsed C C H H H H H H rotation C H H H C H H H staggered The relative orientations of the hydrogens around the two carbons are easier to see in a Newman projection formula , wherein the structure is viewed along the carbon-carbon bond. H H H H H H H H H H H H rotation The intersection of the three bonds represents the orientation of the three H around the front carbon , and the lines to the circle represent the orientation of the three H around the back carbon .
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Ch_322a_4.011 - Sigma Bonds and Bond Rotation Rotation is...

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