Resonance Structures: 4 Rules On How To Evaluate Them, With Practice
There are four key factors that determine the importance of resonance structures in organic chemistry: full octets are preferred,. How stable are the negative and positive charges?
1. Recall The Three “Legal” Electron-Pushing Arrow “Moves” Used For Interconverting Resonance Structures
I’ve been learning about resonance, which is a way of describing the “movement” of electrons in a molecule by using curved arrows to move electrons from a single bond to a lone pair, a lone pair to a pi bond, and a pi bond to a u03c9 bond.
2. Remember That Resonance Structures Are Not In Equilibrium With Each Other – They Represent Contributions To An Overall Resonance “Hybrid”
The molecule’s “true” state will be a “hybrid” of these resonance forms, such as the acetate and allyl cation examples below, where the “true structure” is represented by a 50:50 combination of the two resonance forms.
3. Not All Resonance Forms Are Of Equal Significance. So How Do We Evaluate How “Important” Each One Is?
Because both resonance forms of the acetate ion and the allyl cation have the same energy, the “hybrid” is a 1:1 mixture of the two. Consider the ketone below (acetone, or “propanone”), for which we can draw three different resonance forms.
4. Rule #1: Neutral Resonance Structures Are More “Important” Than Charged Resonance Structures
Because of the dipole-dipole Van der Waals attractive forces, acetone (u20131u00b0C), which has a similar molecular weight, is much higher-boiling than butane (u20131u00b0C), which has a similar molecular weight.
5. Rule #2: Full Octets Are Preferable To Empty Octets (And Never, Ever Have Empty Octets On Oxygen or Nitrogen!)
Resonance forms with full octets will be more significant; never place less than a full octet on nitrogen or oxygen; these resonance forms are extremely unstable and will be insignificant because these atoms are highly electronegative.
6. Rule #3: Place Negative Charges On The Atom Best Able To Stabilize It (i.e. The Least Basic Atom)
Given that neutral resonance structures are preferred in general, if a resonance structure absolutely must bear a negative charge somewhere, place it on the atom best able to stabilize that charge, which is the same as saying “put the negative charge on the least basic atom,” because “basicity is the opposite of stability.”
What are the rules for drawing resonance structures?
The hybridization of the structure must remain the same, the skeleton of the structure cannot be changed (only the electrons move), and resonance structures must have the same number of lone pairs.
Is SO3 a resonance?
Answer: (SO3)2- has three resonance structures, one for each structure formed when sulfur bonds with oxygen in a double bond.
What are three exceptions to the octet rule?
Molecules with an odd number of electrons, such as NO; molecules in which one or more atoms possess more than eight electrons, such as SFsub>6/sub>; and molecules in which one or more atoms possess less than eight electrons, such as BClsub>3/sub>, are the three general exceptions to the octet rule.
Does 03 have a resonance structure?
Ozone, or O3, has two major resonance structures that both contribute equally to the overall hybrid structure of the molecule, accounting for the required 18 valence electrons (six from three bonds and twelve from lone pairs on the oxygen atoms).
What is equivalent resonance?
Any two or more stages between the complete displacement of a charge over an unsaturated alkyl group or between an alkyl and a non-alkyl group are known as equivalent resonance structures.
Which resonance structure is the most stable?
Resonance Structure Stability Estimation Rules
- The resonance structures with complete valence shells for all atoms are more stable.
- The structures with the fewest formal charges are more stable.
- The structures with a negative charge on the more electronegative atom are more stable.
What is a contributing resonance structure?
Resonance contributor (resonance structure; canonical form; canonical structure) is a Lewis structure that differs only in the distribution of electrons in covalent bonds and lone pairs.
How do you draw all Lewis structures?
What Is a Lewis Structure and How Do I Draw One?
- Step 1: Determine the Total Number of Valence Electrons.
- Step 2: Determine the Number of Electrons Required to Make the Atoms “Happy.”
- Step 3: Determine the Number of Bonds in the Molecule.
- Step 4: Select a Central Atom.
- Step 5: Draw a Skeletal Structure.
- Step 6: Arrange Electrons Around Outside Atoms.
What are the 3 types of organic compounds?
Carbohydrates, lipids, proteins, and nucleic acids are the four main types of organic compounds found in all living things; however, other organic compounds may be found in or produced by some organisms.
What is a shorthand formula?
The skeletal formula of an organic compound, also known as the line-angle formula or shorthand formula, is a type of molecular structural formula that serves as a shorthand representation of a molecule’s bonding and some molecular geometry details.
Is water an organic compound?
Water is clearly an inorganic compound (dihydrogen oxide), and methyl alcohol is clearly an organic compound.