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resonance structure question

Discussion in 'Pre-Medical - MD' started by pbehzad, Sep 25, 2002.

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  1. pbehzad

    pbehzad Faddayy
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    When you are doing resonance structures, is it better to have a neutral charge on the entire molecule and have one atom without an octet, or is it better for all the atoms to have an octet and there be a formal charge on an atom(s)? The molecule I am questioning is H2CN2.
    The molecule will be neutral if the second N has 2 valence pairs, and is bonded singly to the other N, but it would not have an octet. If there is a double bond between the two N's, one of the Ns will be (+), and other will be (-) but both Ns will have octets. Got my first orgo test tomorrow :rolleyes: Thanks for any help!
     
    #1 pbehzad, Sep 25, 2002
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  2. Nik

    Nik Member
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    N can violate the octet rule I believe. Regardless, It is always better never to not have a charge (in most cases anyway).
     
    #2 Nik, Sep 25, 2002
  3. Raptor

    Raptor Found one
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    I should be the master of resonance structure after many dern practice. But about your question, the most stable resonance structure is the one with less distribution of charge (neutral will be very stable). Good luck on your test, hope you do great.
     
    #3 Raptor, Sep 25, 2002
  4. Kirk

    Kirk Senior Member
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    Molecules will almost always have an octet. Any atom without an octet is a vicious, nasty, mean electron scavenger. It will NOT be stable. A molecule will be much more stable with a charge then without an octet.
     
    #4 Kirk, Sep 25, 2002
  5. pbehzad

    pbehzad Faddayy
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    Ok so which one is it? raptor and nik say one thing and kirk says the other? dont you love organic chemistry:rolleyes: !
     
    #5 pbehzad, Sep 25, 2002
  6. kidsmd

    kidsmd Senior Member
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    #6 kidsmd, Sep 25, 2002
  7. Raptor

    Raptor Found one
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    What I am trying to say is that when molecules that has an octet, they are stable. A molecule with a charge isn't stable because its always trying to lose or gain e-. Now in resonance structure, if the instructur give a question like, "Which one of these resonance structures are the most stable?" then the resonance structure that has no charge or neutral is stable and the molecule that has a charge is less stable then the one that doesn't.
     
    #7 Raptor, Sep 26, 2002
  8. dpark74

    dpark74 Senior Member
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    Your specific example CH2N2 should have charges. There should be a negative charge (-1) on C and a positive charge (+1) on the N attached to the C.

    Diazomethane people...come on; used to convert carboxylic acids (mostly) to methyl esters.
     
    #8 dpark74, Sep 26, 2002
  9. dpark74

    dpark74 Senior Member
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    NO violates the octet rule. (only 7 around N, and 8 around O)

    Also, CH2N2: no way it can be neutral (ie, no charges) and all atoms have octets.
     
    #9 dpark74, Sep 26, 2002
  10. pbehzad

    pbehzad Faddayy
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    my prof said that it is better to have octets than no charge on teh atoms. she said the H2CN2 molecule was neutral anyways cause the (+) and (-) charges cancelled each other out. Thanks for your help.
     
    #10 pbehzad, Sep 26, 2002
  11. dpark74

    dpark74 Senior Member
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    Yeah..sorry for not making myself clear...overall CH2N2 is neutral but has formal charges on C and N
     
    #11 dpark74, Sep 26, 2002
  12. Phaedrus

    Phaedrus Member
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    It is ALWAYS better to have a full octet, than no charge. You MUST have a full octet, even if it means giving C and N charges.
     
    #12 Phaedrus, Sep 26, 2002
  13. Harps

    Harps Jatt Denominator
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    Molecules that have no charges on any of the ATOMS, but don't have an octet can still be very very stable (some atoms violate the octet rule as has already been said in one of the above posts). But if you can get all atoms to have octets and have the molecule be OVERALL neutral then that is even better. Meaning some atoms will have charges but they cancel out. Anyways, the best resonance structures are usually easy to pick out of the choices because these are ones with complete octets or overall neutral charge--generally.
    Hope this kinds of sums up the confusion and the related clarification regarding resonance structures. Good luck:p
     
    #13 Harps, Sep 26, 2002
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