NonCovalent Interactions

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Non-Covalent Interactions
Interactions that do not involve the sharing of
valence electrons
Strength
Hydrogen bonds gt Dipole-dipole
interactions gt London forces
H-Bonds, dipole-dipole interactions, and London
forces are all weaker than covalent bonds
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Hydrogen Bonds
Interaction of a N, O, or F atom with a H atom
covalently bonded to an N, O, or F

Intermolecular H-Bonds Why water forms
beads, has a high boiling point, and dissolves
many polar and ionic compounds
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Hydrogen Bonds
Interaction of a N, O, or F atom with a H atom
that is covalently bonded to an N, O, or F
Can a methanol molecule form H-bonds with another
molecule of methanol? Can methanol form H-bonds
with water?
Methanol
Can a trimethylamine molecule form H-bonds with
another molecule of trimethylamine? Can
trimethylamine form H-bonds with water?
Trimethylamine
Can an acetone molecule form H-bonds with another
molecule of acetone? Can acetone form H-bonds
with water?
Acetone
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DNA Double Helix is Held Together by Hydrogen
Bonds
H-bond donor NH
H-bond acceptor O
H-bond acceptor O
H-bond donor NH
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Dipole-Dipole Interactions
Attraction of partial positive and partial
negative charges between molecules Partial
charges are permanent
Electronegativity
Cl gt H
O gt C
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London Forces (Van Der Waals Forces)
Attraction of induced partial positive and
partial negative charges between
molecules Partial charges are TEMPORARY

• All molecules exhibit London Forces
• London forces increase with higher surface area

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London Forces
propane
pentane
Can propane and pentane form H-bonds?
Will they have dipole-dipole interactions?
Will they have London Forces? Which has the
higher boiling point? (-42 C, 36 C)
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London Forces
n-Pentane C5H12
Neopentane C5H12
Which has the higher boiling point?
(10 C, 36 C)
London forces increase with greater surface area
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Van Der Waals Forces Allow Geckos to Walk Upside
Down Across a Glass Surface
Millions of setae (microscopic hairs) on the toes
of geckos - extremely high surface area allows
dry adhesion to polar and non-polar surfaces.
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Organic Compounds
Organic compounds contain carbon and
hydrogen.
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Hydrocarbons are One Group of Organic Compounds
Hydrocarbons contain only carbon and
hydrogen.
Alkanes Single carbon-carbon bonds Saturated A
lkenes Double carbon-carbon bonds Unsaturated A
lkynes Triple carbon-carbon bonds Unsaturated A
romatics Ring of alternating single and
Unsaturated double carbon-carbon bonds
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Alkanes
Only C-H and C-C single bonds - nonpolar Not
water soluble hydrophobic Used as fuel
combustion (cars, gas stoves, etc)
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Nomenclature
Prefixes Number of C atoms Prefix 1 meth 2
eth 3 prop 4 but 5 pent 6 hex 7 hept 8
oct 9 non 10 dec
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Alkanes
General formula of alkanes is CnH2n2
Molecular Formula Alkane CH4 methane CH3CH3
ethane CH3CH2CH3 propane CH3CH2CH2CH3
butane CH3CH2CH2CH2CH3 pentane CH3CH2CH2CH2C
H2CH3 hexane CH3CH2CH2CH2CH2CH2CH3 heptane CH3C
H2CH2CH2CH2CH2CH2CH3 octane CH3CH2CH2CH2CH2CH2CH2
CH2CH3 nonane CH3CH2CH2CH2CH2CH2CH2CH2CH2CH3
decane
Condensed structures of alkanes are illustrated
above
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Multiple Ways to Draw Structures
Line bond structure Condensed
structure Skeletal structure
CH3CH2CH2CH2CH3
C atoms are points (ends of lines) H atoms are
implicit
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Constitutional Isomers are DIFFERENT COMPOUNDS
There is more than one structure for
C5H12. Normal pentane (n-pentane) is linear
CH3CH2CH2CH2CH3 Can also draw branched
structures for C5H12.
Draw other structures for C5H12
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Conformations are the SAME COMPOUND Oriented
Differently Due to Bond Rotations
Illustrate for butane