(19) session 19 halo-alkanes, ethers & amines (1)

3/28/2012
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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
2
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

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HaloHaloHaloHalo----alkanesalkanesalkanesalkanes
(Alkyl Halides)(Alkyl Halides)(Alkyl Halides)(Alkyl Halides)
Importance??Importance??Importance??Importance??
4
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

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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
• 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
6
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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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)
8
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
Fluoroalkanes – least reactive

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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)
Halo-alkane C: Tetrahedral geometry
: 109.5°°°° bond angle
10
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
# 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:
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----alkanesalkanesalkanesalkanes
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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
EthersEthersEthersEthers

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Dimethyl ether (methoxymethane):
An aerosol spray propellant
Disadvantage 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
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:
ethyl methyl ether diethyl ether
tert-butyl isobutyl ether
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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

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Examples:
2-methoxybutane 1-ethoxy-3-methyl-pentane
1,4-diisopropoxybutane
O
O
1,4-dimethoxybenzene
(p-dimethoxybenzene)
Physical properties of ethersPhysical properties of ethersPhysical properties of ethersPhysical 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 derWaals forces & dipole-dipole
interactions must be overcome)

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Boiling point comparison of Ethers & Hydrocarbons:
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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

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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)
AminesAminesAminesAmines

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Many amines are biologically active:
=>
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 trigonal
pyramidal
• Partial negative charge (δ-) = localised in region of lone pair e-

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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)
28
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
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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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

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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 #
32
Examples:

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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:
Physical properties of aminesPhysical properties of aminesPhysical properties of aminesPhysical 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

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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
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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

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Basicity: Amines are weak organic bases
Basic mechanism:
Donates an e- pair & accepts
a proton (H+)
Thank you
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END

(19) session 19 halo-alkanes, ethers & amines (1)

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