(21) session 21 carboxylic acids & carboxylic acid derivatives i

5/2/2012
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Session 21
Organic Chemistry, UNAM School of Medicine1
Carboxylic Acids &Carboxylic Acids &Carboxylic Acids &Carboxylic Acids &
Carboxylic Acid Derivatives ICarboxylic Acid Derivatives ICarboxylic Acid Derivatives ICarboxylic Acid Derivatives I
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 what a carbonyl group, acyl group &
carbonyl compound is
Understand the importance of carboxylic acids & its
derivatives
Describe the structure of carboxylic acids & its derivatives
Name carboxylic acids & its derivatives according to IUPAC
system
Organic Chemistry, UNAM School of Medicine
Carbonyl
Compounds I
Carbonyl
Compounds I

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TerminologyTerminologyTerminologyTerminology
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Carbonyl group – a C double
bonded to an O
Carbonyl compound – compound
containing a carbonyl group
Acyl group – carbonyl group
attached to an alkyl group or to an
aryl group
4
Carbonyl compounds:Divided into 2 classes
Class I carbonyl compounds = acyl group is attached to an atom
or a group that can be replaced by another group

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Carbonyl compounds:Divided into 2 classes
Class II carbonyl compounds = acyl group is attached to a
group that can not be readily replaced by another group
Carboxylic AcidsCarboxylic AcidsCarboxylic AcidsCarboxylic Acids
6 Organic Chemistry, UNAM School of Medicine

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Importance??Importance??Importance??Importance??
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Carboxylic acids – found widely throughout nature
(S)-(+)-Lactic acid: Responsible
for the burning sensation felt in
muscles during anaerobic exercise
Oxalic acid: Contained in spinach
& other leafy green vegetables
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Succinic acid & citric acid: Important intermediates in the
citric acid cycle
Prostaglandins: Hormones that stimulate inflammation, cause
hypertension & produce pain

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p-Aminobenzoic acid: Used in
sunscreens; absorbs
short-wavelength UV light
Gamma-aminobutanoic acid (GABA):
A prominant inhibitory neurotransmitter
Structure of carboxylic acidsStructure of carboxylic acidsStructure of carboxylic acidsStructure of carboxylic acids
& derivatives& derivatives& derivatives& derivatives
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Functional group of carboxylic acids consists of a C=O with -OH
bonded to the same C
Carboxyl group is usually written -COOH
Aliphatic acids - alkyl group bonded to -COOH
Aromatic acids - aryl group bonded to -COOH

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11
Carbonyl carbon in carboxylic acids & carboxylic acid
derivatives is sp2 hybridised
Uses its 3 x sp2 orbitals to form σ bonds to the carbonyl O, the α-C &
a substituent (R)
3 atoms attached to carbonyl C are in the same plane & their bond
angles are each approximately 120°
Carbonyl oxygen is also sp2 hybridised
1 of its sp2 orbitals forms a σ bond with the carbonyl C & each of the
other 2 sp2 orbitals contains a lone pair e-
Remaining p orbital of carbonyl O overlaps with remaining p orbital
of carbonyl C to form a π bond

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Structure + bonding of carboxylic acidsStructure + bonding of carboxylic acidsStructure + bonding of carboxylic acidsStructure + bonding of carboxylic acids
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The two most important structural features of the carbonyl
group are:
Nomenclature ofNomenclature ofNomenclature ofNomenclature of carboxylic acidscarboxylic acidscarboxylic acidscarboxylic acids
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Common names - carboxylic acids having 6 or fewer C are
frequently called by their common names.These names were
chosen by early chemists to describe some feature of the
compound, usually its origin
Examples:

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15
Common names - position of a substituent is designated by a
lowercase Greek letter & the carbonyl C is not given a designation.
C adjacent to carbonyl C is the α-C, C adjacent to α-C is the β-C
& so on
C
16
Examples:

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17
Systematic names (IUPAC) - named by replacing the terminal
“e”of the alkane name with “oic acid”
Position of a substituent is designated by a #.
Carbonyl C of a carboxylic acid is always carbon # 1.
C
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Examples:

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Systematic names (IUPAC) …cont’d
- Cyclic carboxylic acids:Add “carboxylic acid-” to the name of the
cyclic compound
Examples:
20
-Aromatic acids: Named as derivatives of benzoic acid
Examples:
benzoic acid p-aminobenzoic acid
(4-aminobenzoic acid)
o-hydroxybenzoic acid
(2-hydroxybenzoic
acid)

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21
-Aliphatic dicarboxylic acids: Named by adding the suffix “-dioic
acid” to the name of the parent alkane
Examples:
22
- Cyclic dicarboxylic acids: Carboxyl groups are treated as
substituents on the cyclic structure
Examples:

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EstersEstersEstersEsters
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Esters – also commonly found in nature
Many of the fragrances of flowers & fruits are due to esters

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Structure of estersStructure of estersStructure of estersStructure of esters
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Esters (R-COOR') have an −OR' group in place of the −OH
group of a carboxylic acid (R-COOH)
Esters can be cyclic or acyclic
Hybridisation structure: Refer to Slides 11-12
Nomenclature ofNomenclature ofNomenclature ofNomenclature of estersestersestersesters
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Common names - name of the group (R') attached to the
carboxyl oxygen (from an alcohol) is stated first, followed by the
name of the acid, with “ic acid” replaced by “ate”
Examples:

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Common names - cyclic esters are called lactones. Derived from
the common name of the carboxylic acid, which designates the length
of the carbon chain, & a Greek letter to indicate the C to which the
carboxyl oxygen is attached
β-lactones = 4-membered ring lactones
γ-lactones = 5-membered ring lactones
δ-lactones = 6-membered ring lactones
Examples:
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Systematic names (IUPAC) - named by naming the R’ group
(from an alcohol) as an alkyl group first followed by the acid name
(the R-C group) with ending “–oate”
Remember:
“Alkyl alkanoate”
Examples:

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Systematic names (IUPAC) - cyclic esters are named as“2-
oxacycloalkanones”. Replace “alk”-part with amount of C’s in
ring
“oxa” = Used to designate the O atom
Examples:
AmidesAmidesAmidesAmides

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Amino acids are linked together
by amide bonds to form
peptides & proteins
Caffeine: Naturally occurring amide
found in cocoa & coffee beans
Penicillin G (‘normal’ penicillin):
Compound with two amide bonds
Structure of amidesStructure of amidesStructure of amidesStructure of amides
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Amides (R-CONH2) have a −NH2, −NHR or −NR2 group in place
of the −OH group of a carboxylic acid (R-COOH)
Amides can be cyclic or acyclic

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Structure of amidesStructure of amidesStructure of amidesStructure of amides
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Amide classification:
primary (1°) = 1 x C group bonded to amide N atom
secondary (2°) = 2 x C groups bonded to amide N atom
tertiary (3°) = 3 x C groups bonded to amide N atom
Nomenclature of amidesNomenclature of amidesNomenclature of amidesNomenclature of amides
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Common & Systematic names (IUPAC) - use the acid name,
replacing “oic acid” or “ic acid” with “amide.” For acids ending
with “carboxylic acid,”“ylic acid” is replaced with “amide”
Entire name – written as one word!
Examples:

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Common & Systematic names (IUPAC) …cont’d
- For substituents bonded to the N - name of the substituent is
stated 1st followed by the name of the amide
- If there is more than 1 substituent bonded to the N, they are stated
alphabetically
- Name of each substituent bonded to N is preceded by an“N” (in
italics) indicating that the group is bonded to a N rather than to a
C
36
Examples:

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- Cyclic amides are called “lactams” in common nomenclature
- Nomenclature is similar to that of lactones
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- Named as “2-azacycloalkanones” in systematic nomenclature
- “aza” = Used to designate the N atom
Examples:

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Acyl HalidesAcyl HalidesAcyl HalidesAcyl Halides
Structure of acyl halidesStructure of acyl halidesStructure of acyl halidesStructure of acyl halides
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Acyl halides – not commonly found in nature, because of their
high reactivity
Acyl halides (R-COX) have a −X in place of the −OH group of a
carboxylic acid (R-COOH)
Acyl chlorides & acyl bromides - most common acyl halides

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Nomenclature ofNomenclature ofNomenclature ofNomenclature of acyl halidesacyl halidesacyl halidesacyl halides
41
Common & Systematic names (IUPAC) - named by using the
acid name & replacing “ic acid” with “yl chloride”(or “yl
bromide”)
-Acids ending with “carboxylic acid” – replace “carboxylic acid”
with “carbonyl chloride” (or “bromide”)
Examples:
Reactivity ofReactivity ofReactivity ofReactivity of acyl halidesacyl halidesacyl halidesacyl halides
42
Acyl halides = activated derivatives of carboxylic acids
Halogen atom (X) of an acyl halide inductively withdraws e- density
from carbonyl C, enhancing its electrophilic nature
This makes acyl halides particularly reactive toward nucleophilic
acyl substitution
Halide ion - serves as a good leaving group

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Electrophile = “electron-lover”
= reagent/atom attracted to electrons
= accepts an electron pair from a nucleophile
= By definition: Lewis acids
= + charged species such as H+, NH4
+or atom that
carries a partial positive charge
Nucleophile = “nucleus-lover”
= donates an electron pair to an electrophile to
form a chemical bond
= By definition: Lewis bases
= Molecules or ions with a free pair of electrons
44
Nucleophile = can be either − charged (:Nu-) or neutral (:Nu)
= if neutral: Usually carries a H atom that can
subsequently be eliminated (:Nu-H)
Examples:
Some − charged
nucleophiles:
Some neutral
nucleophiles:

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Nucleophilic acyl substitution:
Acid AnhydridesAcid AnhydridesAcid AnhydridesAcid Anhydrides

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Structure of acid anhydridesStructure of acid anhydridesStructure of acid anhydridesStructure of acid anhydrides
47
Acid anhydrides – not commonly found in nature, because of
their high reactivity
Loss of H2O from 2 carboxylic acid molecules -Acid anhydride
((R-CO)2-O)
“Anhydride” means “without water”
Structure of acid anhydridesStructure of acid anhydridesStructure of acid anhydridesStructure of acid anhydrides
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Types of acid anhydrides:
Symmetrical anhydride - the 2 COOH molecules forming the
acid anhydride are the same
Mixed anhydride - the 2 COOH molecules forming the acid
anhydride are different

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Nomenclature ofNomenclature ofNomenclature ofNomenclature of acid anhydridesacid anhydridesacid anhydridesacid anhydrides
49
Common & Systematic names (IUPAC)
- Symmetrical anhydrides: Named by using the acid name &
replacing “acid” with “anhydride”
- Mixed anhydrides: Named by stating the names of both acids in
alphabetical order, followed by “anhydride”
Examples:
Reactivity ofReactivity ofReactivity ofReactivity of acid anhydridesacid anhydridesacid anhydridesacid anhydrides
50
Acid anhydrides = activated derivatives of carboxylic acids (like
acyl halides)
However, acid anhydrides are not as reactive as acyl halides
In acyl chloride - Cl atom activates carbonyl (C=O) group &
serves as a leaving group
In acid anhydride - carboxylate group serves these functions

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NitrilesNitrilesNitrilesNitriles
Structure of nitrilesStructure of nitrilesStructure of nitrilesStructure of nitriles
52
Nitriles – compounds that contain a cyano (C=N) functional
group
– considered carboxylic acid derivatives because, like all
Class I carbonyl compounds, they react with H2O
(hydrolyse) to form carboxylic acids

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Structure of nitrilesStructure of nitrilesStructure of nitrilesStructure of nitriles
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Nitriles:
– C & N of cyano group are sp hybridised
– R-C-N bond angle is 180° (linear)
– Nitrile structure - similar to that of a terminal alkyne (propyne)
– N atom of nitrile has lone pair e- instead of alkyne H
Nomenclature ofNomenclature ofNomenclature ofNomenclature of nitrilesnitrilesnitrilesnitriles
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Common & Systematic names (IUPAC)
- Common names:The suffix “-ic acid” is replaced by the suffix
“-onitrile”
- Systematic names: Constructed from the alkane name, with the
suffix “-nitrile” added
Examples:

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Nomenclature ofNomenclature ofNomenclature ofNomenclature of nitrilesnitrilesnitrilesnitriles
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- Substituent nomenclature: If it is seen as a substituent in a
molecule, it is called “cyano”
Example:
Thank you
56
END

(21) session 21 carboxylic acids & carboxylic acid derivatives i

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