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CHE-240 Unit 1 Structure and Stereochemistry of Alkanes CHAPTER ONE

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Title: CHE-240 Unit 1 Structure and Stereochemistry of Alkanes CHAPTER ONE


1
CHE-240Unit 1Structure and Stereochemistry of
AlkanesCHAPTER ONE
  • Terrence P. Sherlock
  • Burlington County College
  • 2004

2
Bond Formation
  • Ionic bonding electrons are transferred.
  • Covalent bonding electron pair is shared.

3
Lewis Structures
  • Bonding electrons
  • Nonbonding electrons or lone pairs

Satisfy the octet rule! gt
4
Multiple Bonding
gt
5
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.

6
Electronegativity and Bond Polarity
  • Greater ?EN means greater polarity

gt
7
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

8
Ionic Structures
9
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.

Examplegt
10
Resonance Example
  • The real structure is a resonance hybrid.
  • All the bond lengths are the same.
  • Each oxygen has a -1/3 electrical charge.

    gt

11
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.

Examplegt
12
Major Contributor?
13
Chemical Formulas
  • CH3COOH
  • C2H4O2
  • CH2O gt
  • Full structural formula (no lone pairs shown)
  • Line-angle formula
  • Condensed structural formula
  • Molecular formula
  • Empirical formula

14
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 24C
  • pH -log H3O
  • Strong acids and bases are 100 dissociated.

15
BrØnsted-Lowry Acids and Bases
  • Acids can donate a proton.
  • Bases can accept a proton.
  • Conjugate acid-base pairs.

16
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.

17
Determining Relative Acidity
  • Electronegativity
  • Size
  • Resonance stabilization of conjugate base


    gt

18
Electronegativity
  • As the bond to H becomes more polarized, H
    becomes more positive and the bond is easier to
    break.

19
Size
  • As size increases, the H is more loosely held and
    the bond is easier to break.
  • A larger size also stabilizes the anion.

20
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.

21
Lewis Acids and Bases
  • Acids accept electron pairs electrophile
  • Bases donate electron pairs nucleophile

22
POWER POINT IMAGES FROM ORGANIC CHEMISTRY, 5TH
EDITIONL.G. WADEALL MATERIALS USED WITH
PERMISSION OF AUTHORPRESENTATION ADAPTED FOR
BURLINGTON COUNTY COLLEGEORGANIC CHEMISTRY
COURSEBYANNALICIA POEHLER STEFANIE LAYMAN
CALY MARTIN
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