Electronic Effects
The effect of electrons that are located in the chemical bonds within the atoms of the molecule is termed an electronic effect. The electronic effect is also explained as the effect through which the reactivity of the compound in one portion is controlled by the electron repulsion or attraction producing in another portion of the molecule.
Drawing Resonance Forms
In organic chemistry, resonance may be a mental exercise that illustrates the delocalization of electrons inside molecules within the valence bond theory of octet bonding. It entails creating several Lewis structures that, when combined, reflect the molecule's entire electronic structure. One Lewis diagram cannot explain the bonding (lone pair, double bond, octet) elaborately. A hybrid describes a combination of possible resonance structures that represents the entire delocalization of electrons within the molecule.
Using Molecular Structure To Predict Equilibrium
Equilibrium does not always imply an equal presence of reactants and products. This signifies that the reaction reaches a point when reactant and product quantities remain constant as the rate of forward and backward reaction is the same. Molecular structures of various compounds can help in predicting equilibrium.
![**General Chemistry 1**
**Workshop 7: Bonding**
**Part I: Resonance and Formal Charge**
Lewis structures allow us to represent the bonding in a molecule or ion. Sometimes more than one Lewis structure is needed to adequately represent a given molecule, and the true structure is said to be a resonance hybrid of several Lewis diagrams. Assigning formal charges is a way to evaluate the relative contributions of different Lewis diagrams to the resonance hybrid. In this method, the shared electrons in a covalent bond are arbitrarily divided equally between the two atoms forming the bond; the unshared valence electrons on an atom are exclusively assigned to that atom. Each atom is then assigned a formal charge (F.C.) which equals the difference between the number of valence electrons in the free atom and the number of electrons assigned to the atom in the Lewis structure. The sum of the formal charges for all atoms in a structure MUST equal to the net charge on the molecule or ion.
The Lewis structures are then evaluated based on the following set of rules:
1. The lower the sum of formal charges in a Lewis structure, the more significant the contribution of that Lewis structure to the resonance hybrid will be.
2. Lewis structures with the following features will not have high contribution to the resonance hybrid - unless they are the only possible Lewis structures for the molecule/ion:
(a) positive F.C. on more electronegative atom
(b) negative F.C. on an atom other than the most electronegative one
3. Consider Lewis structures with the following features only if no other structures fit:
(a) an individual F.C. higher than 1
(b) two formal charges of the same sign on adjacent atoms
**Problem.** Cyanate and Fulminate are 2 polyatomic anions comprised of one C, one N and one O. The scaffold for fulminate is (C---N---O)^1- and the scaffold for cyanate is (O---C---N)^1-. Three resonance structures can be drawn for each molecule. Even though you might expect that these anions would be very similar, one is a very stable anion and the other is very unstable. In this problem, we are going to predict and explain their relative stabilities.
**A.** To begin, draw three resonance structures for each polyatomic ion.
**Fulminate, (C---N---O)^1-:**
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