(22) session 22 carboxylic acids & carboxylic acid derivatives ii

5/2/2012
1
Session 22
Organic Chemistry, UNAM School of Medicine1
Carboxylic Acids &Carboxylic Acids &Carboxylic Acids &Carboxylic Acids &
Carboxylic Acid Derivatives IICarboxylic Acid Derivatives IICarboxylic Acid Derivatives IICarboxylic Acid Derivatives II
Dr L.H.A. Prins (Ph.D.)
Dept. of Pharmacy
UNAM
Learning Outcomes
2
By the end of this session, the student should be able to:
Understand the importance of the carboxylic acid
derivatives, namely aldehydes & ketones
Describe the structure of aldehydes & ketones
Name aldehydes & ketones according to IUPAC system
Describe the physical properties of carboxylic acids & all
of its derivatives
Organic Chemistry, UNAM School of Medicine
Carbonyl
Compounds II
Carbonyl
Compounds II

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AldehydesAldehydesAldehydesAldehydes
3 Organic Chemistry, UNAM School of Medicine
Importance??Importance??Importance??Importance??
4
Many compounds found in nature have aldehyde or ketone
functional groups
Vanillin & cinnamaldehyde: Naturally occurring aldehydes

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Structure of aldehydesStructure of aldehydesStructure of aldehydesStructure of aldehydes
5
Aldehyde (R-CHO): Carbonyl C is bonded to a H on the one side
& to an alkyl/aryl group or a H on the other side
Hybridisation structure: Refer to Session 21 (Slides 11-12)
Structure of aldehydesStructure of aldehydesStructure of aldehydesStructure of aldehydes
6
Examples:

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Nomenclature of aldehydesNomenclature of aldehydesNomenclature of aldehydesNomenclature of aldehydes
7
Common names:
- Derived from the common names of carboxylic acids (seeTable on
next slide)
- “ic acid” (or “oic acid”) is substituted for “aldehyde”
- Greek letters - used to give locations of substituents (as with
COOH’s & other COOH derivatives)
Examples:
8

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9
Systematic names (IUPAC):
- Replace the terminal “e” from the name of the parent hydrocarbon
with “al”
- Carbonyl C: Always at the end of the parent hydrocarbon,
therefore always # 1
• Remember:“Alkanal”
• Examples:
10
-Aldehyde group attached to a ring - named by adding
“carbaldehyde” to the name of the cyclic compound
- C to which aldehyde group is attached is carbon “1”
• Examples:

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KetonesKetonesKetonesKetones
Importance??Importance??Importance??Importance??
12
Many compounds found in nature have aldehyde or ketone
functional groups
Camphor: Ketone responsible
for characteristic sweet odour
of the camphor tree

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Structure of ketonesStructure of ketonesStructure of ketonesStructure of ketones
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Ketone (R-COR'): Carbonyl C is bonded to 2 carbon chains or
carbon rings
Hybridisation structure: Refer to Session 21 (Slides 11-12)
Structure of ketonesStructure of ketonesStructure of ketonesStructure of ketones
14
Examples:

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Nomenclature of ketonesNomenclature of ketonesNomenclature of ketonesNomenclature of ketones
15
Common names:
- Name the two alkyl groups attached to the carbonyl group
followed by the word “ketone”
- Greek letters - used to give locations of substituents (as with
COOH’s & other COOH derivatives)
Examples:
ethyl methyl ketone
16
Common names:
- Some ketones have historical common names
- Some of these names are allowed by IUPAC
- Dimethyl ketone is always called “acetone”
-Alkyl phenyl ketones: Named as acyl group followed by suffix
“phenone”
Examples:

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17
- Replace the terminal “e” from the name of the parent hydrocarbon
with “one”
- Number chain to give carbonyl carbon smallest possible #
• Remember:“Alkanone”
• Examples:
18
- Cyclic ketones: Carbonyl C is assumed to be at position # 1
• Examples:

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19
- Ketone as a substituent: If the ketone has a 2nd FG of higher
naming priority, the ketone oxygen is indicated by the prefix
“oxo”
• Examples:
Physical properties of COOHPhysical properties of COOHPhysical properties of COOHPhysical properties of COOH
& COOH derivatives& COOH derivatives& COOH derivatives& COOH derivatives

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Boiling pointsBoiling pointsBoiling pointsBoiling points
21
Carbonyl compounds have the following relative boiling points:
Bp’s of an ester, acyl chloride, ketone & aldehyde are ↓ than bp of
an alcohol with a comparable molecular weight
Reason:Alcohol molecules can form H-bonds with each other
Bp of carbonyl compounds are ↑ than bp of an ether
Reason: Result of the polar carbonyl group
22
Carboxylic acids have relatively high bp’s
Reason: Form intermolecular H-bonds with each other, giving them
larger effective molecular weights (called dimer formation)

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23
Amides have the highest bp’s
Reason: Strong dipole-dipole interactions as a result of resonance
1°°°° & 2°°°° amides can also form intermolecular H-bonds
24
Nitriles have similar bp’s to that of an alcohol
Reason: Nitriles have strong dipole-dipole interactions

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25
Carboxylic acids,Amides & Nitriles: Summary of bp’s
SolubilitySolubilitySolubilitySolubility
26
Carboxylic acid derivatives are soluble in solvents such as
ethers, chlorinated alkanes & aromatic hydrocarbons
Carbonyl compounds with fewer than 4 carbons are soluble in H2O
(corresponding to alcohols & ethers)

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Substituent effects on acidity
27
Substituents have an effect on acidity of carboxylic acids:
COOH
OCH3
COOH COOH
NO2
COOH
NO2
COOH
NO2
p-methoxy benzoic acid m-nitro p-nitro o-nitro
pKa = 4.46 pKa = 4.19 pKa = 3.47 pKa = 3.41 pKa = 2.16
Substituent effects on acidity
28
Substituents have an effect on acidity of carboxylic acids:
-NH2, -NHR, -NR2
-OH
-OR electron donating
-NHCOCH3
-C6H5
-R
-H
-X
-CHO, -COR
-SO3H
-COOH, -COOR electron withdrawing
-CN
-NR3
+
-NO2

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Reactivity of COOH derivativesReactivity of COOH derivativesReactivity of COOH derivativesReactivity of COOH derivatives
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Leaving group is an anion
The weaker the base, the better the leaving group
The better the leaving group, the more reactive the carbonyl
compound
R2 N
-
RO
-
O
RCO
-
X
-
Increasing basicity
Increasing leaving ability
Reactivity of COOH derivativesReactivity of COOH derivativesReactivity of COOH derivativesReactivity of COOH derivatives
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Halide ion - weakest base & best leaving group
Therefore: Acyl/acid halides are the most reactive toward
nucleophilic acyl substitution
Amide ion - strongest base & poorest leaving group
Therefore: Amides are the least reactive toward nucleophilic
acyl substitution

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Reactivity of aldehydes & ketonesReactivity of aldehydes & ketonesReactivity of aldehydes & ketonesReactivity of aldehydes & ketones
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Aldehydes – less steric hindrance
– Higher reactivity towards nucleophiles
Ketones – more steric hindrance
– lower reactivity towards nucleophiles
Thank you
32
END

(22) session 22 carboxylic acids & carboxylic acid derivatives ii

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