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OrgChem Lec
Acids and Bases
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Cards (28)
Bronsted-Lowry Acid
Proton donor
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Bronsted-Lowry Base
Proton acceptor
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Conjugate acid
Formed when a base accepts a proton from a suitable donor
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Conjugate base
Formed when an acid loses a proton
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Equilibrium constant
(Ka)
Measure of the strength of an acid in dilute aqueous solution
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Strong acids
Characterized by large values of Ka, essentially every molecule transfers a proton to water
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Weak acids
Have small Ka values
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pKa
Convenient way to express acid strength, equal to -log(Ka)
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Relative strength of an acid and its conjugate base
The
stronger
the acid, the
weaker
the conjugate base. The
weaker
the acid, the
stronger
the conjugate base.
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Electrophile
Loves electrons, acid
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Nucleophile
Attacks molecules with positive charge, base
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Factors affecting acidity in binary compounds
Bond length (
shorter
= stronger, lower acidity)
Bond strength (
longer
= weaker, higher acidity)
Bond polarity (smaller
electronegativity
difference favors
higher
acidity)
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Push-pull electronic effects on the proton
Affect the strength of
oxyacids
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Ranking 1.0M solutions of HBrO, HIO and HClO in order of increasing pH
HIO
<
HBrO
<
HClO
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Acid strength
Ability to donate a proton to water, expressed by Ka or pKa
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Positivity
of H
The more positive the H, the more acidic and the higher the acid strength
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Stability of conjugate base
The more stable the
conjugate base
, the more willing the acid is to donate its
proton
, the higher the
acid strength
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Electronic effects
Electron
release
or electron donating effect (+)
increases
electron density
Electron withdrawal
or electron accepting effect (-)
decreases
electron density
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Resonance effect
+R
groups render the benzene ring
more
electron rich, especially at
ortho
and
para
positions
-R
groups render the ring
less
electron rich, especially at
meta
positions
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Inductive effect
Inhibited by -I EN atoms/groups, groups with orbital EN, groups with excess + charge
+I effect exhibited by groups with excess - charge, alkyl groups
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Steric
effects
Generally associated with bulky groups, can exhibit -I, +R but +R>-I, net effect is electron release or withdrawal
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Acidic form
Predominates when pH < pKa
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Buffer solution
Maintains a nearly
constant pH
within certain parameters
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Lewis acid
Electron
pair
acceptor
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Lewis base
Electron
pair
donor
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Basicity
Tendency to
donate
an
electron pair
, exhibited by amines with a lone pair on N
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Factors affecting basicity
Presence of electron
releasing
groups makes the electron pair
more
available, hence more basic
Presence of electron
withdrawing
groups makes the electron pair
less
available, hence less basic
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Bonsted-Lowry Acids and Bases is also known as
Protonic
Theory