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Aldehydes Aldehydes && KetonesKetones contain the carbonyl group, C=O.
R-C-H R-C-R’
or RCHO or R-CO-R’
O O
Aldehyde Ketone
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Both aldehydes and ketones contain the carbonyl group, C=O.
The H-C=O group of an aldehyde is called the formyl group.
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Aldehyde Nomenclature1. Find longest Carbon chain that
includes C of C=O.
2. Ending for name is “al” : alkane + al --> alkanal
3. Number chain to give C of C=O locant #1.
4. Aldehyde & ketone more important than alcohol group.
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Example of Naming Aldehydes
HO-CH2-CH2CH2CH-CH2CH2-CH
O
CH3
7-hydroxy-4-methylheptanal
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Ketone Nomenclature
1. Find longest Carbon chain that includes C of C=O.
2. Ending for name is “one” : alkane + one --> alkanone
3. Number chain to give C of C=O the lower possible locant.
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Example
CH3CH2CHCH2CCH2CH3
O
5-phenyl-3-heptanone
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Aldehyde & Ketone Bonding
* Carbon has 120° bond angles
* molecular shape around C is trigonal planar
O=C
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The C=O bond is polar covalent, has permanent dipole because of electronegativity difference between C and O....
C O–+
••••
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Aldehyde & Ketone Reactions
1. Oxidation
2. Reduction
3. Addition
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Oxidation means carbon forms more bonds to oxygen.
Aldehydes are easilyeasily oxidized to carboxylic acids:
R-C-H R-C-O-H
O O[O]
.
[O] means add oxygen from [O] means add oxygen from another source, like Oanother source, like O22..
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Ketones are NOT easily oxidized.
Reagents which oxidize aldehydes do NOT oxidize ketones.
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Reduction means forming more C-H bonds or decreasing the number of C-O bonds.
R-C-H R-CH-HH
O OHH[H]
aldehyde ---> primary alcoholaldehyde ---> primary alcohol
[H] means add H from another source
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R-C-R’ R-C-R’
O OHH
HH
[H]
ketone ---> secondary alcoholketone ---> secondary alcohol
Ketone Reduction
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Practice Problem
Draw the structure of the product of this reaction:
O
CH3CH2CCH2CH2CH3
[H]???
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Ketones are reduced to alcohols.
So: what is the alcohol related to the ketone shown?
CH3CH2CCH2CH2CH3
OH
H
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Addition Reactions of Aldehydes & Ketones
C=O++
––
electron pair donor (nucleophile) reacts at C
•• •• e– pair acceptor
(electrophile, often H+) reacts at O
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Alcohols add to the C=O of aldehdyes and ketones
RORO-HH symbol for alcohol ••
••
Electrophile at H
Nucleophile at O because electron pair donor
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General Reaction for ROH addition happens in 2 steps…
R-C-H + RORO-HH
OH+ (catalyst)
R-C-H
OROR
O-HH
hemi-acetal hemi-acetal
(product of first step)
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General Reaction for ROH addition, 2nd step is
R-C-H R-C-H + H2O
OROR OROR
O-HH OROR
hemi-acetalhemi-acetal acetalacetal
ROROH, H+
2nd step
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Example:
What hemi-acetal is formed in the reaction
CH3CH2C-H + CH3OH
O???
Hint:
RO of alcohol bonds to C of C=O,
H bonds to O of C=O
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CH3CH2C-H
OCH3
OH
CH3CH2C-H + CH3OH
OSo, the answer is:
Hemi-acetal
2222
Notes:• ordinarily, hemi-acetals are ordinarily, hemi-acetals are not not stable enough to stable enough to isolate from isolate from reaction.reaction.
• product usually obtained is product usually obtained is acetal.acetal.
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Formation of acetals is Formation of acetals is reversiblereversible: they can be decomposed simply by reversing the steps which led to their formation.
Formation uses excess ROH.Formation uses excess ROH.
Decomposition or hydrolysis Decomposition or hydrolysis uses excess Huses excess H22O.O.
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Example of Hydrolysis of Acetals:
C HOCH3
OCH3 H2O, H+
C-H + 2 CH3OH
O
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Ketones make hemi-acetals and acetals as well.
Predict structure of the acetal from the unbalanced reaction below:
CCH2CH3 + CH3OH
OH+
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CCH2CH3
OCH3
OCH3
Here ya go!
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