Anonymous
Anonymous asked in Science & MathematicsChemistry · 1 decade ago

lack of rotation?

Why does the lack of free rotation in alkenes lead to existence of E/Z stereoisomers?

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  • 1 decade ago
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    Stereoisomerism about double bonds arises because rotation about the double bond is restricted, keeping the substituents fixed relative to each other. If the substituents on either end of a double bond are the same, it is not considered a stereo bond.

    An example of double bond stereoisomerism is 1,2-dichloroethene, C2H2Cl2. Molecule I is Z-1,2-dichloroethene (chlorines on same side - the top) and molecule II (chlorines on opposite sides) is E-1,2-dichloroethene. There is no way of "superimposing" the structures on each other through bond rotation, because of the central double bond of C=C (composed of a sigma bond and a pi bond), through which rotation is not allowed. If rotation were allowed, such as a single bond would allow, these two molecules would be the same.

    --Yamakiri

  • 1 decade ago

    The restriction of the double bond prevents the rotation. For the structure to rotate, the bond must first break.

    The isomers arise from the fact that the 3D structure of them is different. It affects the symmetry, and in many cases the polarity and the electron distribution, which leads to different properties.

  • 1 decade ago

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  • 1 decade ago

    Because the e/z prevents it

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  • Anonymous
    1 decade ago

    not sure.

  • 1 decade ago

    dunno

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