Selected Electronegativity Values

1
Selected Electronegativity Values
Increasing electronegativity
Increasing electronegativity
2
Differences in electronegativity leads to
polarity of bonds
En 2.2
Carbon is more electronegative than hydrogen
En 2.6
Bond Dipole moment points toward carbon
Bond Classification
?En 0 - 0.4 nonpolar covalent ?En 0.4 - 2
polar covalent ?En gt2 ionic
3
Combination of bond polarities determines the
overall molecular polarity
For methane, all of the bond dipole moments
cancel, therefore the molecule is nonpolar
For water, all of the bond dipole moments do not
cancel, therefore the molecule is polar
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Molecular Drawings
Condensed
Kekulé
Bond-Line Formula
5
Functional groups and family name (or class)
table Table 2.3 p. 66
alkene
alcohol
Carboxylic acid
ketone
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Resonance
-Electron movement or distribution between
multiple bonds (delocalized electrons) -We can
write individual resonance structures however
none actually exist independent of the other -The
Resonance Hybrid is an overall description of
electronic distribution based on the individual
resonance structures
Example acetate anion, carbonate anion, enolate
anion
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Chapter 2 - Alkanes
Nomenclature - Naming of chemical
compounds Functional Groups- Table 2-3, p.
66 Common Alkanes - Table 2-3, p.69 Chains vs.
groups, Table 2-6, p. 70 IUPAC Rules
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IUPAC Rules
1. Identify and Name longest carbon chain(stem
chain) 2. Number the longest chain from the end
that is closest to a group 3. Name all groups
attached to the longest chain 4. Alphabetize the
groups 5. Name the molecule by beginning with the
numbered alphabetized groups and add the name of
the longest chain.
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Nomenclature Info
Common Groups
1. Identify and Name longest carbon chain(stem
chain) 2. Number the longest chain from the end
that is closest to a group 3. Name all groups
attached to the longest chain 4. Alphabetize the
groups, group prefixes are ignored 5. Name the
molecule by beginning with the numbered
alphabetized groups and add the name of the
longest chain.
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Bond Rotation-ethane
Rotation about single bonds is very fast at room
temperature
The end methyl (CH3) groups are like pinwheels
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Bond Rotation Terms and Newman Projections-ethane
Terms Staggered, Eclipsed, and Gauche
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Bond Rotation Energetics - ethane
TS-transition state
Changes in energy are due to electrostatic
repulsion of atoms and bonds
Room temperature provides 20 kcal of energy
13
Bond Rotation - butane
gauche
anti
eclipsed
gauche
eclipsed
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Bond rotation energetics - butane
High energy conformers - unstable
eclipsed
Low energy conformers - stable
gauche
anti
anti
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Two types of Bond Cleavage
Homolytic bond cleavage
Heterolytic bond cleavage
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Radical Reaction Mechanism - Chlorination of
Methane
Initiation
Propagation
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Termination
backwards
product
by-product
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One method of Determining Energetics of Reaction
?H bonds broken - bonds made
Propagation
?H C-H - Cl-H 105 kcal/mol - 103 kcal/mol 2
kcal/mol
?H Cl-Cl - Cl-C 58 kcal/mol - 85 kcal/mol
-27 kcal/mol
Bond energies listed in Table 3-1and Table 3-2,p.
95 and Table 3-4,p. 107
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Reaction Coordinate for Chlorination of Methane
Activation energy(Ea)
Overall energy change Of reaction (?HR)
The propagation steps are the steps in which
reactants go to products, this is where the
energy changes occur not in the initiation or
termination steps
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Bond Dissociation Energies- DH
1 kcal 1 Cal (food calorie)
98 Cal in can of Miller Lite
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Additional Bond Dissociation Energies
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Rates of Halogenation
23
Halogenation Energy Changes
Bromination
Fluorination