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Shweta Thakur posted an Question
May 03, 2020 • 18:53 pm 30 points
  • IIT JAM
  • Chemistry (CY)

Why allene is non planar also say about its steriochemistry

why Allene is non planar also say about its sterio chemistry

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    Dinesh khalmaniya 1 best-answer

    No, VSEPR theory does not allow for a coplanar arrangement. Let us consider allene and its orbitals: check image Hybridization The terminal carbons are sp2sp2 hybridized, and form three σσ-bonds each. This means that each terminal carbon has one unhybridized pp-orbital. The central carbon atom is spsp hybridized, and forms two σσ-bonds. This means it has two unhybridized pp-orbitals. For our sake, we will call these two orbitals pxpx and pypy. These orbitals are perpendicular to one another. π-Bonds A ππ-bond is the result of the sharing of two pp-electrons, and it is particularly important for us to consider them as belonging to a particular region of space. In order for the central carbon's pxpx-electron to form a ππ-bond with one of the terminal carbons, it must be with another pxpx-electron. If the two did not share the same spacial orientation no bond could form. Since the xx-dimension is occupied by the electrons of a ππ-bond between the central carbon and one of the terminal carbons, the only way for the central carbon to form an additional ππ-bond is by sharing its pypy-electron with the other terminal carbon. Hence, the two terminal carbons are necessarily perpendicular to one another.

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