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pi backbonding

  • 09-01-2005 06:29PM
    #1
    dinoflagellates
    Closed Accounts Posts: 13 ✭


    Hi there,
    hate asking people this but what is pi backbonding? is it where two electrons move go back into an empty pi orbital or is it where two elctrons in a pi bond go back into an empty orbital or are both right
    Thanks very much i have searched the web to no avail.
    Also does anyone know any good science search engines


Comments

  • #2
    Capt'n Midnight
    Moderators, Recreation & Hobbies Moderators, Science, Health & Environment Moderators, Technology & Internet Moderators Posts: 95,993 Mod ✭✭✭✭Capt'n Midnight


    Going by memory - can lookup the book later.

    In carbon you have 1s , 2s and three P shells
    When all four valancies are used with Single bonds the outer four shells hybridise together to form four equal energy electron pairs. Because it's 4 the structure is tetrahydral.

    With other hybridisations of shells you get different structures. With a Double bond (and two single bonds) there are three shells involved and so you get three bonds about 120 degrees apart. - You can imagine the double bond as a single bond with electron clouds above and below it forming the other one.

    With a tripple bond again you have a single bond and electron clouds above and below, but this time with others to each side - and the bond angle is 180 degrees.

    Not clearly explained
    the images on these sites aren't that clear either
    http://dl.clackamas.cc.or.us/ch106-02/pibonds.htm
    http://dl.clackamas.cc.or.us/ch106-02/structur2.htm

    http://www.wellesley.edu/Chemistry/chem120/hybrids.html - images are better


  • #3
    Zaphod
    Registered Users, Registered Users 2 Posts: 1,733 ✭✭✭Zaphod


    Pi backbonding is a bonding interaction between the d orbitals of a metal and Pi* orbitals of a ligand.

    So in the case of CO as the ligand, you generally get a sigma bond where the ligand donates the electron pair of the carbon into the empty orbital of the metal, while the metal back donates electrons from filled d orbitals into the Pi* orbital of CO.

    More info:
    http://www.ilpi.com/organomet/carbonyl.html


  • #4
    dinoflagellates
    Closed Accounts Posts: 13 ✭dinoflagellates


    thanks very much, that is what i was looking for!!!!!


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