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Resonance question? Organic chemistry?

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asked Sep 10, 2015 in CHEMISTRY by anonymous

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A resonance form is another way of drawing a Lewis dot structure for a given compound. Equivalent Lewis structures are called resonance forms. They are used when there is more than one way to place double bonds and lone pairs on atoms.

Rules for drawing additional resonance forms :

    1. Draw the Lewis structure of the molecule and we have the first resonance contributor.

    2. Only electrons move. Atoms never move.

    3. Only pi electrons and lone pair electrons can move, sigma bonds (single bonds) never move.

    4. The total number of electrons of the overall atom does not change (the charge). Therefore, all resonance contributors have the same charge.

    5. Electrons only move towards an sp2  carbon. That means that they can only move towards a positively charged atom or a double bonded one (usually a carbon).

Draw the additional resonance forms for the structure using the rules.

In the above resonance form has a lone pair of electrons.

Convert the lone pair of electrons into π bond.

answered Sep 10, 2015 by yamin_math Mentor
edited Sep 10, 2015 by yamin_math
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Resonance Hybrids :

Resonance Structures are a representation of a Resonance Hybrid, which is the combination of all resonance structures.

The resonance structure with the Formal Charge closest to zero is the most accepted structure, however, the correct Lewis structure is actually a combination of all the resonance structures and is not solely describe as one.

     1. Draw the Lewis Structure & Resonance for the molecule (using solid lines for bonds).

     2. Where there can be a double or triple bond, draw a dotted line (-----) for a bond.

     3. Draw only the lone pairs found in all resonance structures, do not include the lone pairs that are not on all of the resonance structures.

Draw the resonance structure.

Draw the resonance hybrid for the above resonance circuit using the rules specified in the resonance hybrid.

Add only the pi- bonds found on all resonance structures.

Replace the pi- bonds with dotted line.

answered Sep 10, 2015 by yamin_math Mentor
edited Sep 10, 2015 by yamin_math

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