Week 2
Chemistry Note
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Chemical reactions occur due to the giving, taking, and/or sharing of electrons
Different effects influence the distribution of electrons in a covalent bond of an organic molecule
Polarity within a molecule leads to electron transfer among atoms, resulting in different behavior compared to non-polar compounds
Saturated hydrocarbons are nonreactive due to the lack of polarity in C-C and C-H bonds
Charged species react with polar organic molecules due to an imbalance in electron density or polarity
Elements with higher electronegativity can change the electron density around an organic molecule and make it more reactive
Factors influencing electron availability include electron displacement effects or electronic effects
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Substituent effects on reactivity occur through electronic and steric effects
Electronic effects can stabilize a molecule, affect its volatility, and influence its acidity or basicity
Understanding electronic imbalance is important for predicting reaction products and behavior of organic molecules
Inductive effect is a type of electronic effect where partial polarities are developed on atoms joined by a single covalent bond
Inductive effect can be transmitted along a carbon chain and decreases with distance from the source atom
Inductive effect can be electron-withdrawing (-I) or electron-releasing (+I)
Relative inductive effects have been experimentally measured with reference to hydrogen
Inductive effect can determine the stability or instability of a molecule depending on the charge and type of groups bonded to an atom
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Inductive effect can amplify or de-amplify the charge on an atom, affecting the stability of the molecule
Resonance effect, also known as mesomeric effect, occurs when a molecule can be represented by multiple structures that differ in electron arrangement
Mesomeric effect is due to the polarity developed in the molecule by the interaction of pi-bonds separated by a single bond or a pi-bond and a lone pair of electrons
Different structures resulting from resonance effect are known as resonance structures
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Inductive effect and resonance effect (mesomeric effect) are two factors influencing electron availability in organic molecules
Inductive effect involves the partial polarities developed on atoms joined by a single covalent bond
Resonance effect occurs when a molecule can be represented by multiple structures that differ in electron arrangement
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Mesomeric effect is a permanent effect that makes compounds more stable
Mesomeric effect is negative (-M) for electron-withdrawing groups
Examples: acetyl, nitrile, nitro
Mesomeric effect is positive (+M) for electron-releasing groups
Examples: alcohol, amine, benzene
Localized electrons belong to a single atom or are confined to a bond between two atoms
Delocalized electrons are shared by more than two atoms and result in resonance
Resonance hybrid is a composite of resonance contributors with different locations of lone-pair and Pi electrons
Electron delocalization occurs if all atoms sharing delocalized electrons lie in or close to the same plane
Cyclooctatetraene is not planar and has tub-shaped structure due to inability of p orbitals to overlap
Rules for drawing resonance contributors:
Atoms maintain their position, only outer shell electrons move
Only non-bonding electrons, π electrons, and lone-pair electrons can move
Total number of electrons and numbers of paired and unpaired electrons do not change
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Canonical forms must be valid Lewis structures
Not all canonical forms contribute equally to the actual molecule, stability determines contribution
Rule 1: The most significant resonance contributor has the greatest number of full octets
Rule 2: The most significant resonance contributor has the fewest atoms with formal charges
Rule 3: Negative formal charges on more electronegative atoms and positive formal charges on less electronegative atoms are more stable
Rule 4: The most significant resonance contributor has the greatest number of bonds
Rule 5: If a pi bond is present, it is more significant if it is between atoms of the same row of the periodic table
Rule 6: Aromatic resonance contributors are more significant than non-aromatic ones
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Rule 3 (continued): Negative formal charge on oxygen is more significant than on carbon
Rule 4 (continued): Four covalent bonds are more significant than three covalent bonds
Rule 5 (continued): Carbon-fluorine double bond is more significant than carbon-chlorine double bond
Rule 6 (continued): Aromatic resonance contributors are more
What causes chemical reactions to occur? Answer: The giving, taking, and/or sharing of electrons.
How does polarity within a molecule affect its behavior? Answer: It leads to electron transfer among atoms, resulting in different behavior compared to non-polar compounds.
Why are saturated hydrocarbons nonreactive? Answer: Due to the lack of polarity in C-C and C-H bonds.
What causes charged species to react with polar organic molecules? Answer: An imbalance in electron density or polarity.
How can elements with higher electronegativity affect the reactivity of an organic molecule? Answer: They can change the electron density around the molecule and make it more reactive.
What factors influence electron availability in organic molecules? Answer: Electron displacement effects or electronic effects.
How do substituents affect reactivity? Answer: Through electronic and steric effects.
What can electronic effects do to a molecule? Answer: Stabilize it, affect its volatility, and influence its acidity or basicity.
What is the inductive effect? Answer: A type of electronic effect where partial polarities are developed on atoms joined by a single covalent bond.
How does the inductive effect change with distance from the source atom? Answer: It decreases with distance.
What are the two types of inductive effect? Answer: Electron-withdrawing (-I) and electron-releasing (+I).
How are relative inductive effects measured? Answer: With reference to hydrogen.
How can the inductive effect determine the stability of a molecule? Answer: Depending on the charge and type of groups bonded to an atom.
What is the resonance effect? Answer: When a molecule can be represented by multiple structures that differ in electron arrangement.
What causes the resonance effect? Answer: The interaction of pi-bonds separated by a single bond or a pi-bond and a lone pair of electrons.
What are the different structures resulting from the resonance effect called? Answer: Resonance structures.
What are the two factors influencing electron availability in organic molecules? Answer: Inductive effect and resonance effect.
What is the mesomeric effect? Answer: A permanent effect that makes compounds more stable.
Is the mesomeric effect negative or positive for electron-withdrawing groups? Answer: Negative (-M).
Chemistry Note Mind Map:
Central Idea: Factors influencing electron availability in organic molecules
Main Branches:
Chemical reactions and electron distribution
Polarity and behavior of molecules
Reactivity of saturated hydrocarbons
Charged species and polar organic molecules
Electronegativity and reactivity of organic molecules
Factors influencing electron availability
Sub-branches:
1.1 Giving, taking, and sharing of electrons
2.1 Electron transfer and behavior in polar compounds
3.1 Lack of polarity in C-C and C-H bonds
4.1 Imbalance in electron density or polarity
5.1 Higher electronegativity changing electron density
6.1 Electron displacement effects
6.2 Electronic effects
Main Branches:
Substituent effects on reactivity
Electronic effects on molecules
Inductive effect
Resonance effect
Sub-branches:
7.1 Electronic and steric effects
8.1 Stabilization, volatility, acidity, and basicity
9.1 Partial polarities on atoms joined by a single covalent bond
9.2 Decrease with distance from the source atom
9.3 Electron-withdrawing (-I) and electron-releasing (+I)
9.4 Measured with reference to hydrogen
9.5 Determine stability based on charge and type of groups
10.1 Multiple structures with different electron arrangement
10.2 Interaction of pi-bonds or pi-bond and lone pair
10.3 Resonance structures
Main Branches:
Inductive effect and resonance effect
Mesomeric effect
Sub-branches:
11.1 Factors influencing electron availability
11.2 Partial polarities on atoms joined by a single covalent bond
11.3 Multiple structures with different electron arrangement
12.1 Permanent effect making compounds more stable
12.2 Negative (-M) for electron-withdrawing groups
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12.3 Positive (+M) for electron-releasing groups
12.4 Localized and delocalized electrons
12.5 Resonance hybrid and electron delocalization
12.6 Cyclooctatetraene and inability of p orbitals to overlap
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12.7 Rules for drawing resonance contributors
12.8 Canonical forms and stability
12.9 Most significant resonance contributor
12.10 Octets, formal charges, and