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Chapter 1 Introduction and Review

Organic Chemistry , 5 th Edition L. G. Wade, Jr. Chapter 1 Introduction and Review. Jo Blackburn Richland College, Dallas, TX Dallas County Community College District ã 2003, Prentice Hall. =>. Definitions. Old: “derived from living organisms” New: “chemistry of carbon compounds”

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Chapter 1 Introduction and Review

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  1. Organic Chemistry, 5th EditionL. G. Wade, Jr. Chapter 1Introduction and Review Jo Blackburn Richland College, Dallas, TX Dallas County Community College District ã 2003,Prentice Hall

  2. => Definitions • Old: “derived from living organisms” • New: “chemistry of carbon compounds” • From inorganic to organic, Wöhler, 1828 Chapter 1

  3. => Atomic Structure • protons, neutrons, and electrons • isotopes Chapter 1

  4. 2s orbital (spherical) => 2p orbital Atomic Orbitals Chapter 1

  5. => Electronic Configurations • Aufbau principle: Place electrons in lowest energy orbital first. • Hund’s rule: Equal energy orbitals are half-filled, then filled.    Chapter 1

  6. Table 1-1 => Chapter 1

  7. => Bond Formation • Ionic bonding: electrons are transferred. • Covalent bonding: electron pair is shared. Chapter 1

  8. Lewis Structures • Bonding electrons • Nonbonding electrons or lone pairs Satisfy the octet rule!=> Chapter 1

  9. Multiple Bonding => Chapter 1

  10. => Dipole Moment • Amount of electrical charge x bond length. • Charge separation shown by electrostatic potential map (EPM). • Red indicates a partially negative region and blue indicates a partially positive region. Chapter 1

  11. Electronegativity and Bond Polarity Greater EN means greater polarity => Chapter 1

  12. => Calculating Formal Charge • For each atom in a valid Lewis structure: • Count the number of valence electrons • Subtract all its nonbonding electrons • Subtract half of its bonding electrons Chapter 1

  13. X => Ionic Structures Chapter 1

  14. Resonance • Only electrons can be moved (usually lone pairs or pi electrons). • Nuclei positions and bond angles remain the same. • The number of unpaired electrons remains the same. • Resonance causes a delocalization of electrical charge. Example=> Chapter 1

  15. Resonance Example • The real structure is a resonance hybrid. • All the bond lengths are the same. • Each oxygen has a -1/3 electrical charge. => Chapter 1

  16. Major Resonance Form • has as many octets as possible. • has as many bonds as possible. • has the negative charge on the most electronegative atom. • has as little charge separation as possible. Example=> Chapter 1

  17. major minor, carbon does not have octet. => Major Contributor? Chapter 1

  18. Full structural formula (no lone pairs shown) Line-angle formula Condensed structural formula Molecular formula Empirical formula CH3COOH C2H4O2 CH2O => Chemical Formulas Chapter 1

  19. Calculating Empirical Formulas • Given % composition for each element, assume 100 grams. • Convert the grams of each element to moles. • Divide by the smallest moles to get ratio. • Molecular formula may be a multiple of the empirical formula. => Chapter 1

  20. => Arrhenius Acids and Bases • Acids dissociate in water to give H3O+ ions. • Bases dissociate in water to give OH- ions. • Kw = [H3O+ ][OH- ] = 1.0 x 10-14 at 24°C • pH = -log [H3O+ ] • Strong acids and bases are 100% dissociated. Chapter 1

  21. conjugate acid conjugate base acid base => BrØnsted-Lowry Acids and Bases • Acids can donate a proton. • Bases can accept a proton. • Conjugate acid-base pairs. Chapter 1

  22. pKa 4.74 pKb 3.36 pKb 9.26 pKa 10.64 => Acid and Base Strength • Acid dissociation constant, Ka • Base dissociation constant, Kb • For conjugate pairs, (Ka)(Kb) = Kw • Spontaneous acid-base reactions proceed from stronger to weaker. Chapter 1

  23. Determining Relative Acidity • Electronegativity • Size • Resonance stabilization of conjugate base => Chapter 1

  24. => Electronegativity As the bond to H becomes more polarized, H becomes more positive and the bond is easier to break. Chapter 1

  25. => Size • As size increases, the H is more loosely held and the bond is easier to break. • A larger size also stabilizes the anion. Chapter 1

  26. => Resonance • Delocalization of the negative charge on the conjugate base will stabilize the anion, so the substance is a stronger acid. • More resonance structures usually mean greater stabilization. Chapter 1

  27. nucleophile electrophile => Lewis Acids and Bases • Acids accept electron pairs = electrophile • Bases donate electron pairs = nucleophile Chapter 1

  28. End of Chapter 1 Chapter 1

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