OChem Chp 1

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OChem Chp 1
2014-01-31 21:44:45
Organic Chemistry
Berkeley Chapter 1
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  1. primary (1°) carbon
    • a carbon with one other carbon attached
    • secondary (2°) = two other carbons attached
    • tertiary (3°) = three other carbons attached
  2. covalent bond
    • a bond in which electrons are shared evenly between two atoms
    • a bond is covalent when the difference in electronegativity between two atoms is LESS than 1.5
    • the 2 atoms generally have little to no difference in electronegativity
  3. What are the 2 types of covalent bonds?
    • sigma: the electron density is shared between the nuclei of the two atoms
    • pi bonds: there is no electron density shared between the nuclei of the two atoms, but instead only above and below the internuclear region
  4. polar-covalent (partially ionic) bond
    when the difference in electronegativity between two atoms is greater than 1.5 but less than 2.0
  5. "sigma bond first" rule
    • the first type of bond to form between atoms is usually the sigma bond
    • pi bonds are the second bond present in double bonds & the second and third bonds present in triple bonds
  6. What molecule is the exception to the "sigma bond first" rule?
    • fluorine gas: molecular fluorine (F2) has only one π-bond, with no σ-bond present b/c of small it is & its inter-nuclear repulsion
    • the bond dissociation energy of F2 is less than the bond dissociation energy of Cl2, even
    • though Cl is below F in the periodic table
  7. relative strengths of bonds
    • longer bonds are weaker bonds: the longer the bond, the less the electron density overlaps between nuclei, thus the weaker the bond
    • triple bond > double bond > single bond
  8. VSEPR Theory
    • C requires 4 electron pairs in the form of bonds
    • N requires one lone pair + three bonds
    • O requires 2 lone pairs + 2 bonds
    • HONC-1234 to be NEUTRAL
  9. Charged Atoms
    • having too many bonds in a molecule results in a cation & too few bonds results in an anion EXCEPT w/ carbon
    • if O makes 3 bonds & has 1 lone pair → carries a positive charge
    • if N makes 2 bonds & has 2 lone pairs → carries a negative charge
    • if C makes 3 bonds & has a lone pair → anion
    • if C makes 3 bonds & doesn't have a lone pair → cation
  10. Borane
    • the boron atom has only 3 valence electrons, so a NEUTRAL boron CANNOT satisfy the octet rule
    • boron has sp2-hybridization for its 3 sigma bonds, but NO pi bond
  11. energy is ________ when a bond is formed & that energy must be ________ by the molecule to break a bond
    • when a bond is formed energy is released
    • when a bond is broken energy is absorbed
  12. Enthalpy of a Reaction Formula
    ΔHReaction = ΣEnergy(bonds broken) - Energy(bonds formed)
  13. Bond Dissociation Energy
    • the larger the bond dissociation energy, the STRONGER a bond
    • the most stable bond is the one that requires the greatest energy to break
  14. ionic bond
    • a bond in which electrons are transferred from one atom to another - are formed between 2 oppositely charged ions (common between metals & nonmetals)
    • a bond is ionic when the difference in electronegativity between two atoms is GREATER than 2.0
    • the greater the charge on an ion, the STRONGER the bond
    • ionic bonds are typically stronger than covalent bonds however b/c ions can be solvated in a polar, protic solvent, ionic bonds are often cleaved MORE READILY than covalent bonds (in a protic environment)
  15. Resonance
    when electron density is shifted through regions of the molecule via π-bonds (delocalization of electrons through a continuous array of overlapping p-orbitals, π-bonds, & adjacent lone pairs)
  16. Fonclbrisch
    • F > O > N > Cl > Br > I > S > C > H
    • most to least electronegative
    • most F > Cl > Br > I > least electronegative
  17. If a molecule contains a negative charge, where is the best atom for it to be on?
    the most electronegative atom
  18. If a molecule contains a positive charge, where is the best atom for it to be on?
    the least electronegative atom
  19. The Inductive Effect
    • induces charge separation in a molecule
    • a highly electronegative atom pulls electron density from its neighbor, which in turn pulls electron density from its neighbor
    • considered most when a molecules contains a halogen
  20. Steric Hinderance
    occurs any time two atoms attempt to be in the same place at the same time; is repulsive in nature & increases as the atoms draw closer
  21. Aromaticity
    • stability generated from having 4n + 2π electrons in a continuous, overlapping ring of p-orbitals, where n is any integer including 0 (Huckel rule)
    • an energy level is completely filled when there are 4n + 2π electrons in the cyclic π-network
  22. Bronsted-Lowry Acid
    • proton donor
    • a compound that has a hydrogen which can be lost as H+
    • eg. H - Cl
  23. Bronsted-Lowry Base
    • proton acceptor
    • a compound that has electrons available to form a bond to H+
    • b/c a lone pair of electrons is necessary to form a bond to the proton, all Bronsted-Lowry bases are ALSO Lewis bases
  24. 5 Strong Acids in OChem
    • strong
    • H2SO4
    • HI
    • HBr
    • HCl
    • HNO3
    • weak
  25. when comparing 2 conjugate pairs, the pair with the stronger acid has the weaker conjugate base (as a Bronsted-Lowry acid gets stronger, it loses a proton more readily so its conjugate base is LESS willing to gain a proton)
  26. Lewis Base
    • electron pair donor
    • a compound that has electrons available to form a bond to an electron deficient atom (such as, but not exclusively, H+)
  27. Lewis Acid
    • electron pair acceptor
    • can have a protic hydrogen or may have an empty valence shell capable of accepting electrons (eg. BF3)
  28. pKa 5-10-15-20 Rule
    • carboxylic acid pKa ~ 5
    • phenol pKa ~ 10
    • alcohol pKa ~ 15
    • alpha protons/carbonyl pKa ~ 20
  29. Acidity & Bond Length
    • the more s-character in the hybrid orbital of the atom bonded to hydrogen, the STRONGER the acid
    • stronger sp > sp2 > sp3 weakest
    • as a hybrid orbital gets smaller, electrons are held closer to the nucleus of the atom bonded to hydrogen, so the bond can be cleaved in a heterolytic fashion more easily
  30. Acidity & Basicity
    • the more acidic a compound is, the more easily it can lose a hydrogen
    • electron-withdrawing groups increase acidity
    • electron-donating groups increase basicity
    • the stronger an acid the lower its pKa
    • the stronger an acid the greater its Ka
  31. Resonance & Electron Withdrawing/Donating
    • an adjacent atom making a π-bond is electron-withdrawing
    • an adjacent atom with a lone pair is electron-donating
    • *resonance is a more significant factor than the inductive effect when determining acidity
  32. alkyl groups are electron-________
    alkyl groups are electron-donating, therefore they REDUCE the acidity of a compound