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Session 19
Organic Chemistry, UNAM School of Medicine1
HaloHaloHaloHalo----alkanes (Alkyl Halides), Ethers & alkanes (Alkyl Halides), Ethers & alkanes (Alkyl Halides), Ethers & alkanes (Alkyl Halides), Ethers &
AminesAminesAminesAmines
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 halo-alkanes, ethers &
amines
�Describe the structure of halo-alkanes, ethers & amines
�Name halo-alkanes, ethers & amines according to
IUPAC system
�Describe the physical properties of halo-alkanes, ethers &
amines
Organic Chemistry, UNAM School of Medicine
3/28/2012
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HaloHaloHaloHalo----alkanes alkanes alkanes alkanes
(Alkyl Halides)(Alkyl Halides)(Alkyl Halides)(Alkyl Halides)
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Importance??Importance??Importance??Importance??
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� Halogen-substituted organic compounds – widespread
throughout nature� ± 5000 halo-alkanes have been found in algae & various other
marine organisms
� Halogen-containing compounds - vast array of industrial applications, including their use as solvents, inhaled anaesthetics in medicine, refrigerants & pesticides
Organic Chemistry, UNAM School of Medicine
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Importance??Importance??Importance??Importance??
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� In spite of all the useful applications, some fluoroalkanes (Freons®)
are detrimental to earth’s upper ozone layer & are banned from use in most parts of the world
� Chlorofluorocarbons (CFCs) - Cl atoms initiate a reaction chain that damages the ozone layer, which is needed to protect life on earth
from harmful UV rays
Organic Chemistry, UNAM School of Medicine
• Hydrochlorofluorocarbon (HCFC) &
hydrofluorocarbon (HFC) compounds
such as CF3CHCl2 & CF3CH2F - now
being used as CFC replacements
Structure of haloStructure of haloStructure of haloStructure of halo----alkanesalkanesalkanesalkanes
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� Halogen (X) might be bonded to:� an alkynyl group (C=C-X),
� a alkenyl group (C=C-X),
� an aromatic ring (Ar-X), or
� an alkyl group (C-X)
� Primarily concerned with alkyl halides (halo-alkanes) -compounds with a halogen atom bonded to a saturated, sp3
hybridised C atom
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Structure of haloStructure of haloStructure of haloStructure of halo----alkanesalkanesalkanesalkanes
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� Halogens ↑ in size going down periodic table (F < Cl < Br <I ) -
lengths of corresponding C-X bonds ↑ accordingly
� Additionaly, C-X bond strengths ↓ going down periodic table
(C-F > C-Cl > C-Br > C-I)
Organic Chemistry, UNAM School of Medicine
Structure of haloStructure of haloStructure of haloStructure of halo----alkanesalkanesalkanesalkanes
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� In order for anything to react with the halo-alkanes, the C-X
bond has to be broken
� Because that gets easier as you go from fluoride (F) to iodide (I),
the compounds get more reactive in that order
Iodoalkanes - most reactive
Organic Chemistry, UNAM School of Medicine
Fluoroalkanes – least reactive
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Structure of haloStructure of haloStructure of haloStructure of halo----alkanesalkanesalkanesalkanes
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� Halogens: More electronegative (EN) than C� C-X bond = polar covalent bond, with C atom bearing a slight +
charge (δ+) & halogen a slight −−−− charge (δ-)
� This polarity results in a substantial dipole moment for all the halomethanes (Table –slide 7)
Organic Chemistry, UNAM School of Medicine
Halo-alkane C: Tetrahedral geometry: 109.5°°°° bond angle
Structure of haloStructure of haloStructure of haloStructure of halo----alkanesalkanesalkanesalkanes
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� Classification of halo-alkanes:
� Primary (1o): X attached to 1o carbon - RCH2-X
� Secondary (2o): X attached to 2o carbon - R2CH-X
� Tertiary (3o): X attached to 3o carbon - R3C-X
Organic Chemistry, UNAM School of Medicine
# of alkyl groups (R) attached to the C to which the X is bonded determines whether a halo-alkane (alkyl halide) is primary, secondary or tertiary
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Nomenclature of haloNomenclature of haloNomenclature of haloNomenclature of halo----alkanesalkanesalkanesalkanes
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� Common names - name of alkyl group, followed by name of halogen - with the “ine” ending of halogen name replaced by “ide” (i.e., fluoride, chloride, bromide, iodide)
� Examples:
� Systematic names (IUPAC) - alkyl halides named as substituted
alkanes (halo-alkanes)
- prefix names for the halogens end
with “o” (i.e. fluoro, chloro, etc.)Organic Chemistry, UNAM School of Medicine
Nomenclature of haloNomenclature of haloNomenclature of haloNomenclature of halo----alkanesalkanesalkanesalkanes
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� Examples:
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I
2-bromo-5-methylheptane 1-chloro-5,5-dimethylhexane(1-chloro-3-neopentylpropane)
1-ethyl-2-iodocyclopentane
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Physical properties of haloPhysical properties of haloPhysical properties of haloPhysical properties of halo----alkanes alkanes alkanes alkanes
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� The polar C–X bond means that halo-alkanes have a substantial
dipole moment
� halo-alkanes are poorly soluble in H2O, but are soluble in
organic solvents (i.e. C-based solvents)
� They have boiling points which are similar to alkanes of
comparable molecular weight
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EthersEthersEthersEthers
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Importance??Importance??Importance??Importance??
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� Dimethyl ether (methoxymethane):An aerosol spray propellantDisadvantage of being flammable
� Diethyl ether (ethoxyethane):A common low boiling solvent (b.p. 34.6°C) & an early anaesthetic
� Anisole (methoxybenzene):A precursor to perfumes, insect pheromones & pharmaceuticals
Organic Chemistry, UNAM School of Medicine
Structure of ethersStructure of ethersStructure of ethersStructure of ethers
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� Ethers (R-O-R) can be considered derivatives of water (H-O-H) or alcohols (R-O-H) by replacing an H with an R group
� R groups in ethers can be: � alkyl (C-C-O-C-C),
� alkenyl (C=C-O-C=C), or
� aryl (aromatic ring) (Ar-O-Ar)
� If R groups are the same (R-O-R): Called symmetrical ethers
� If R groups are different (R-O-R’): Called unsymmetrical ethers
� Ethers can be cyclic or acyclic
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Nomenclature of ethersNomenclature of ethersNomenclature of ethersNomenclature of ethers
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� Common names - consist of the names of the two alkyl
substituents (in alphabetical order), followed by the word “ether”
The smallest ethers are usually named by their common names
� Examples:
Organic Chemistry, UNAM School of Medicine
ethyl methyl ether diethyl ether tert-butyl isobutyl ether
Nomenclature of ethersNomenclature of ethersNomenclature of ethersNomenclature of ethers
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� Systematic names (IUPAC) - named as alkoxy (RO−) substituted alkanes, alkenes & alkynes. The substituents are named by replacing the “yl” ending in the name of the alkyl substituent
with “oxy”
� Remember:
“Alkoxyalkane”, “Alkoxyalkene”, “Alkoxyalkyne”
� The group in the chain that has greatest # of C atoms is designated the parent compound
� In the case of aromatic ethers, the benzene ring is the parent compound
Organic Chemistry, UNAM School of Medicine
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Nomenclature of ethersNomenclature of ethersNomenclature of ethersNomenclature of ethers
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� Examples:
Organic Chemistry, UNAM School of Medicine
2-methoxybutane 1-ethoxy-3-methyl-pentane
1,4-diisopropoxybutane
O
O
1,4-dimethoxybenzene(p-dimethoxybenzene)
Physical properties of ethers Physical properties of ethers Physical properties of ethers Physical properties of ethers
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� Ethers have nearly the same geometry as H2O � R-O-R bonds have an approximately tetrahedral bond angle (112°
in dimethyl ether) & O atom is sp3-hybridised
� The electronegative O atom gives ethers a slight dipole moment� Boiling points of ethers are often slightly higher than boiling points
of comparable alkanes (Van der Waals forces & dipole-dipole interactions must be overcome)
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Physical properties of ethers Physical properties of ethers Physical properties of ethers Physical properties of ethers
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� Boiling point comparison of Ethers & Hydrocarbons:
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Physical properties of ethers Physical properties of ethers Physical properties of ethers Physical properties of ethers
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� Volatility & Solubility:
� H atoms in H2O have ↑ partial + charge than H atoms on ether
� H2O: Charge is localised (only on) the H’s
� Ether: Charge is delocalised (spread throughout) the alkyl groups
� ∴ Charge is stronger in water than in ethers
� Because of delocalised nature of + charge on molecule's H atoms,
the H’s can not partake in H bonding
Organic Chemistry, UNAM School of Medicine
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Physical properties of ethers Physical properties of ethers Physical properties of ethers Physical properties of ethers
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� Volatility & Solubility:
� ∴ Ethers only form H bonds to other molecules that have H atoms with strong partial + charges
� ∴ Ether molecules can not form H bonds with other ether molecules → leads to high volatility of ethers
� Ethers → limited solubility in water (used for extractions during chemical synthesis)
Organic Chemistry, UNAM School of Medicine
AminesAminesAminesAmines
Organic Chemistry, UNAM School of Medicine24
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Importance??Importance??Importance??Importance??
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� Many amines are biologically active:
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=>
Structure of aminesStructure of aminesStructure of aminesStructure of amines
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� Nitrogen (N) atom in an amine is sp3 hybridised• The 3 groups & the unshared e- pair around N result in a tetrahedral
geometry (Molecular geometry)
• If unshared e- pair is not considered - shape of the amine is trigonalpyramidal
• Partial negative charge (δ-) = localised in region of lone pair e-
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Structure of aminesStructure of aminesStructure of aminesStructure of amines
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� Amine classification:
� primary (1°) = 1 x C group bonded to N atom
� secondary (2°) = 2 x C groups bonded to N atom
� tertiary (3°) = 3 x C groups bonded to N atom
� quaternary (4°) = 4 x C groups bonded to N atom (N has + formal charge)
Organic Chemistry, UNAM School of Medicine
Structure of aminesStructure of aminesStructure of aminesStructure of amines
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� Further amine classification:
• Aliphatic amines: amines in which N is bonded only to alkyl groups
• Aromatic amines: amines in which N is bonded to one or more aryl
groups
• Heterocyclic amines: amines in which N is one of the atoms of a ring
Organic Chemistry, UNAM School of Medicine
NH2
Aminobenzene(Aniline)
N
H
N
N-propylpropan-1-amine(Dipropylamine)
Pyrrolidine Pyridine
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Nomenclature of aminesNomenclature of aminesNomenclature of aminesNomenclature of amines
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� Common names - names of the alkyl/aryl groups bonded to N, in alphabetical order, followed by “amine”
Entire name – written as one word! (Unlike common names of
alcohols, ethers & alkyl halides)
� Examples:
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Nomenclature of aminesNomenclature of aminesNomenclature of aminesNomenclature of amines
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� Systematic names (IUPAC)
- Name is based on longest C chain
- “e” of parent hydrocarbon replaced with “amine”
- # identifies the C to which the N is attached
- # can appear before name of parent hydrocarbon or before
“amine”
- name of alkyl group bonded to N - preceded by an“N” (in italics)
indicating that the group is bonded to a N rather than to a C
Organic Chemistry, UNAM School of Medicine
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Nomenclature of aminesNomenclature of aminesNomenclature of aminesNomenclature of amines
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� Examples:
- Substituents:
Listed in alphabetical order, regardless of whether they are
attached to the N or to parent hydrocarbon
A # or an “N” is assigned to each substituent
Chain - numbered in direction that gives functional group suffix
lowest possible #Organic Chemistry, UNAM School of Medicine
Nomenclature of aminesNomenclature of aminesNomenclature of aminesNomenclature of amines
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� Examples:
Organic Chemistry, UNAM School of Medicine
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Nomenclature of aminesNomenclature of aminesNomenclature of aminesNomenclature of amines
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� Systematic names (IUPAC)…cont’d
- If NH2 group is classified as substituent in a compound – called an
amino group
� Examples:
-The common arylamines have the following names:
Organic Chemistry, UNAM School of Medicine
Physical properties of amines Physical properties of amines Physical properties of amines Physical properties of amines
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� Boiling points:
� 1° & 2° amines: Can form H-bonds with each other & H2O
� 3° amines: Can not form H-bonds with each other, but can form H-
bonds with H-bond donors such as H2O
� 3° amines: Have lower boiling points than 1° or 2° amines of
comparable molecular weights
Organic Chemistry, UNAM School of Medicine
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Physical properties of amines Physical properties of amines Physical properties of amines Physical properties of amines
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� H2O Solubility:
� 1°, 2° & 3° amines: Can all form H-bonds with H2O
� Low-molecular weight amines are generally H2O soluble
Organic Chemistry, UNAM School of Medicine
Physical properties of amines Physical properties of amines Physical properties of amines Physical properties of amines
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� Basicity: Amines are weak organic bases � React with H2O to produce alkylammonium ions & hydroxide
anions
� React with acids to produce alkylammonium salts
Organic Chemistry, UNAM School of Medicine
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Physical properties of amines Physical properties of amines Physical properties of amines Physical properties of amines
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� Basicity: Amines are weak organic bases � Basic mechanism:
Organic Chemistry, UNAM School of Medicine
Donates an e- pair & accepts a proton (H+)
Thank you
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END
Organic Chemistry, UNAM School of Medicine