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

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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

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� 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??

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� 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

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� 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

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� Examples:


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Nomenclature of aldehydesNomenclature of aldehydesNomenclature of aldehydesNomenclature of aldehydes

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� Common names:- Derived from the common names of carboxylic acids (see Table 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:



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� 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:



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� Systematic names (IUPAC):- 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??

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� 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

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� Examples:


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Nomenclature of ketonesNomenclature of ketonesNomenclature of ketonesNomenclature of ketones

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� 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


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� 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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� Systematic names (IUPAC):- Replace the terminal “e” from the name of the parent hydrocarbon with “one”

- Number chain to give carbonyl carbon smallest possible #

• Remember: “Alkanone”

• Examples:



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� Systematic names (IUPAC):

- Cyclic ketones: Carbonyl C is assumed to be at position # 1

• Examples:


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� Systematic names (IUPAC):

- 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 COOH Physical properties of COOH Physical properties of COOH Physical properties of COOH

& COOH derivatives& COOH derivatives& COOH derivatives& COOH derivatives


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Boiling pointsBoiling pointsBoiling pointsBoiling points

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� 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



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� 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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� 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



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� Nitriles have similar bp’s to that of an alcohol

� Reason: Nitriles have strong dipole-dipole interactions


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� Carboxylic acids, Amides & Nitriles: Summary of bp’s


SolubilitySolubilitySolubilitySolubility

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� 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

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� 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

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� 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 b asicity

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 nucleophilicacyl 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

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END


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

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