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Questions and Answers
Which element is the most electronegative?
Which element is the most electronegative?
Electronegativity increases as you move from right to left across the periodic table.
Electronegativity increases as you move from right to left across the periodic table.
False
What does a higher electronegativity difference between two bonded atoms indicate?
What does a higher electronegativity difference between two bonded atoms indicate?
The bond is more polar.
The electronegativity of carbon (C) is _____ .
The electronegativity of carbon (C) is _____ .
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Match the bond types with their characteristics:
Match the bond types with their characteristics:
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What does the dipole moment (μ) measure?
What does the dipole moment (μ) measure?
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Symmetrical molecules can have a non-zero dipole moment.
Symmetrical molecules can have a non-zero dipole moment.
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What indicates the direction of bond polarity in electrostatic potential maps?
What indicates the direction of bond polarity in electrostatic potential maps?
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What is the primary cause of the inductive effect?
What is the primary cause of the inductive effect?
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The inductive effect has the same strength regardless of the distance from the source.
The inductive effect has the same strength regardless of the distance from the source.
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What order of stability do carbocations obey?
What order of stability do carbocations obey?
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The __________ effect involves the delocalization of electrons in conjugated systems.
The __________ effect involves the delocalization of electrons in conjugated systems.
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Which of the following statements is true about resonance?
Which of the following statements is true about resonance?
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Match the following concepts with their associated effects:
Match the following concepts with their associated effects:
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Mesomeric effect is defined for saturated compounds only.
Mesomeric effect is defined for saturated compounds only.
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What types of functional groups are classified in relation to the inductive effect?
What types of functional groups are classified in relation to the inductive effect?
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Study Notes
Pharmaceutical Organic Chemistry 1 (Introduction)
- This is an introductory course in Pharmaceutical Organic Chemistry.
- Key formulas include E=mc² and V2.
- H₂O is a molecule mentioned.
Electronegativity
- Electronegativity (EN) is the affinity of an atom for electrons in a covalent bond.
- Differences in electronegativity create bond polarity.
- Fluorine (F) has the highest electronegativity (EN = 4.0).
- Cesium (Cs) has the lowest electronegativity (EN = 0.7).
- Metals on the left side of the periodic table have lower electronegativity and attract electrons weakly.
- Halogens and other reactive non-metals on the right side of the periodic table have high electronegativity and attract electrons strongly.
- EN of Carbon (C) = 2.5
- Electronegativity values are given for various elements in the periodic table.
Effect of Electronegativity on Bond Polarity
- Nonpolar covalent bonds form when the difference in electronegativity between atoms is less than 0.5. Examples include C-H bonds.
- Polar covalent bonds form when the difference in electronegativity is between 0.5 and 2. Examples include C-O, C-X bonds where X is a highly electronegative element.
- Ionic bonds form when the difference in electronegativity is greater than 2.
Polar Covalent Bonds
- Bonding electrons are attracted to the more electronegative atom, creating a partial negative charge (δ-) on that atom and a partial positive charge (δ+) on the other atom.
- Examples of polar covalent bonds include C-F, B-F, and C-O-H
Practice Problems
- Determine if bonds are ionic, polar covalent, or nonpolar covalent. Examples include C-Li, N-H, Na-Br, S-O, and C-H bonds.
Electrostatic Potential Maps
- Electrostatic potential maps show charge distributions.
- Red areas indicate electron-rich regions.
- Blue areas indicate electron-poor regions.
- Arrows indicate bond polarity direction.
- Examples presented include Methanol and Methyllithium.
Dipole Moment (μ)
- Dipole moment measures the net polarity of a molecule.
- It's calculated as the vector sum of individual bond polarities and lone-pair contributions.
- Units are Debye (D).
- Values are given for various molecules like N-H, and F-F.
Applications of Dipole Moments
- Differentiating di-substituted benzene products (with different μ values).
- Assigning configurations of geometrical isomers like C₂H₂Cl₂ (cis- and trans-dichloroethenes).
Absence of Dipole Moments
- In symmetric molecules, dipole moments cancel each other out because the opposing dipoles in the molecule are equal and in opposite directions. Examples include CO₂, CH₄, CCl₄, Ethane, and Benzene.
Electron Displacement Factors
- Factors influencing electron availability (electron density) in bonds or atoms.
- Three factors are discussed: inductive effect, mesomeric effect, and hyperconjugation.
Inductive Effect
- Electron shift in a bond due to electronegativity differences of neighboring atoms.
- This results in a bond polarization effect—one end of the bond has a partial positive or negative charge depending on the surrounding atoms' electronegativity.
- The inductive effect weakens with increasing distance from the source.
- Inductive effects from atoms beyond C2 are often ignored in calculations.
Mesomeric Effect (Resonance)
- Delocalization of electrons in conjugated systems, especially in π bonds.
- Carbonate ion (CO₃²⁻) is used as an example.
Resonance and Stability of Benzene
- Benzene exhibits enhanced stability due to resonance, a feature of its aromatic character.
Resonance and Stability of Carbocations
- Resonance enhances the stability of carbocations like allyl and benzyl carbocations.
- The order of increasing carbocation stability is generally benzylic 3° > allylic 2° > 1° > methyl.
Hyperconjugation
- Stabilizing interaction of σ bonding electrons (typically C-H or C-C) with empty or partially filled p or π orbitals.
- Results in extended molecular orbitals, increasing the stability of the molecule.
- Illustrated in propene.
Contact Information
- Contact information for the instructor (Dr. Aya Almatary) is provided for further questions.
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Description
Explore the fundamentals of Pharmaceutical Organic Chemistry with a focus on electronegativity and its effect on bond polarity. This quiz covers key concepts, important formulas, and the electronegativity values of various elements. Test your understanding of how these factors play a crucial role in chemical bonding.
