Download 1 Organic Compounds – Functional Groups and Physical Properties

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Organic Compounds – Functional Groups and Physical Properties
Allotropes of Carbon – Allotropes are forms of the same element that have different bonding patterns or arrangements. Elemental carbon can exits
in many different allotropes. The allotropes cover a wide range of properties and characteristics. Four allotropes are described as follows:
(i)
Diamond – In diamond, every carbon atom is bonded to four other carbon atoms in a tetrahedral pattern. The covalent bonds between the atoms
are extremely strong, and the arrangement and symmetry of these bonds make diamond unusually strong and hard.
(ii) Graphite – This soft allotrope exists in abundance. In graphite, carbon atoms are arranged in sheets or layers. These layers are held together by
weak attractive forces. Graphite’s structure makes it a good writing material. The layered structure also gives it good lubricating properties as it is
used to make key slide more easily into a lock.
(iii) Amorphous Carbon – This allotrope has no predictable arrangement. It has random bonding pattern. Amorphous carbon is usually produced when
carbon compounds decompose. Examples are: charcoal, soot, bone black (from decomposition of animal bone) and coke (from decomposition of
coal).
(iv) Fullerenes – Fullerenes, also called Buckyballs, are globe-shaped, cage-like arrangements of carbon atoms. A 60-carbon fullerene is found in the
soot. A fullerene has been found to attack an enzyme found in the virus that causes AIDS.
Unique Bonding of Carbon – Carbon’s half-filled valence level and relatively small size give it its unique bonding properties. A carbon atom needs 4
more electrons to satisfy the octet rule. Therefore carbon atoms form exactly 4 covalent bonds with other atoms. These bonds may take the forms of
four single bonds, a double bond and two single bonds, or a triple bond and one single bond. A carbon atom’s electrons fill only two principal energy
levels, so its valence electrons are relatively close to the nucleus. This closeness allows carbon to form short, strong covalent bonds. In addition, a carbon
atom is small enough to share one, two, or three pairs of electrons with other atoms. However, carbon atoms differ from other small atoms because
carbon does not typically exist as diatomic molecule. Only under exceptional circumstances can atoms share four pairs of electrons in a chemical bond. A
pair of carbon atoms would need to share four pairs of electrons to form a stable C2 molecule. Long chains of carbon atoms provide the framework for
an enormous variety of compounds, such as DNA, proteins, carbohydrates, and other compounds.
The Nature of Carbon – Carbon Multiple Bonds: In a carbon-carbon multiple bond, either a double bond or a triple bond, there are two types
of bonds present. These bonding types are known as sigma bonds or pi bonds. There are three key concepts about chemical bonding:
(1) Different types of atomic orbitals are available for electrons to occupy and that these different orbitals types, s, p, d, and f, differ in shape. An
“s” orbital has a spherical shape. A dumbbell shape is associated with a “p” orbital, and so on.
(2) Electron sharing in covalent-bond formation results from the overlap of atomic orbitals. Because of orbital overlap, shared electrons are able
to move around in the area between two covalently bonded atoms.
(3) Single-, double-, and triple-covalent bonds respectively involve the simultaneous overlap of one, two, and three pairs of atomic orbitals.
The manner in which two atomic orbitals overlap in the formation of a covalent bond is what determines whether a given bond is a sigma bond or a pi
bond. A sigma bond is a covalent bond in which the overlap between atomic orbitals lies along the axis joining the two bonded atoms, i.e., end-to-end
overlapping. A pi bond is a covalent bond in which the overlap between atomic orbitals is above and below (but not on) the inter-nuclear axis, i.e., sideby-side overlapping.
(------------------------- sigma bond: three different overlap diagrams ----------------------)
pi bond diagram
The concepts of sigma and pi bonds relate to the various types of bonding that can occur between carbon atoms in the following ways:
(i)
(ii)
(iii)
When only one bond is present (single bond), that bond is always a sigma bond.
When there is a double bond, that bond always consists of one sigma bond and one pi bond, which is formed from
the overlap of one p orbital from each carbon atom.
When there is a triple bond that bond always consists of one sigma bond and two pi bonds, which are formed from
the overlap of two p orbitals from each carbon atom.
For a carbon that has 4 single bonds, all of the
orbitals are hybrids.
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Nonmetals and Pi Bonds
Carbon, oxygen, and nitrogen all have an unusual ability to form double bonds. In an atom of any of these elements, the p orbitals of the electrons
available for bonding are in the second shell, not too far from the atom’s nucleus. If we drop down to the third row of the periodic table to silicon, sulfur
and phosphorus, the p orbitals of the bonding electrons are farther away from the nucleus in shell three. Therefore, when third-level p electrons go into
pi bonds, they cannot be as effective in holding nuclei near other as when the p electrons come from the second level. Thus, pi bonds formed by the
overlap of third shell p orbitals are not as strong as those made from second shell p orbitals.
Organic Compounds - Three main components of Functional Groups:
(1) Multiple Bonds between C atoms
−C = C −
Unlike single −C − C − bonds, double and triple bonds allow atoms to be added to the chain, making
−C ≡ C −
these compounds more reactive, while – C – C – single bond is strong covalent bond and not reactive
(2) C atoms bonded to a more electronegative atom (O, N, halogens)
(3) C atom double-bonded to an O atom
C=O
The resulting polar bond increases boiling point and melting point.
Oxidation and Reduction in Organic Reactions
In general, oxidation numbers are seldom used in oxidation and reduction reactions for organic compounds. The focus is always on the increase or
decrease in electron density caused by the addition or loss of hydrogen and oxygen (or other electronegative) atoms. The following guidelines are useful
in deciding whether a particular organic reaction is an oxidation or reduction process.
(1) A carbon atom in an organic compound is oxidized if it gains oxygen (or other electronegative) atoms or loses hydrogen atoms in a chemical
reaction.
(2) A carbon atom in an organic compound is reduced if it loses oxygen (or other electronegative) atoms or gains hydrogen atoms in a chemical
reaction.
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Organic Compounds
Hydrocarbons
(contain only carbon & hydrogen)
Aliphatic Hydrocarbons
Acyclic
Cyclic
(straight or branched structure)
(has closed ring structure)
Alkanes
(“paraffins”)
Alkenes
(“ethylenes”
or “olefins” )
C−C
C=C
Alkynes
(“acetylenes”)
cycloalkanes
cycloalkenes
Hydrocarbon Derivatives
Aromatic Hydrocarbons
Benzenes &
its derivatives
Polynuclear Aromatic
hydrocarbons
(“fused” benzene rings)
C≡C
An alkyl group is a hydrocarbon group derived from an alkane by the removal of a hydrogen atom; often a substitution group or branch on an organic
molecule. An aryl group is an aromatic ring from which one hydrogen atom has been removed.
Examples:
CH3CH3
CH2 = CH2
Ethane
Ethylene
HC ≡ CH
Acetylene
Benzene
Naphthalene
Alkanes are called saturated hydrocarbons and Alkenes and Alkynes are called unsaturated hydrocarbons. Alkanes with branched carbon chains are
called branched alkanes. Alkanes change their shape when a single carbon-carbon bond rotates about its axis. When two structures differ only by one or
more bond rotations, they are said to be conformations of each other. Structural isomers are compounds having the same molecular formula, but their
atoms bond in different orders. For example, pentane, 2-methylbutane, and 2,2-dimentylpropane are structural isomers because they all have the same
formula, C5H12 . Hydrocarbons that contains a carbon ring are called cyclic hydrocarbons, e. g. the cyclic hydrocarbons with only single bonds are called
cycloalkanes. Benzene is the most common and stable unsaturated cyclic hydrocarbon.
The aromatic hydrocarbons are benzene and compounds containing a benzene ring. Benzene has the chemical formula C6H6 and consists of a ring of six
carbon atoms. Based on the chemical formula, one proposed structure for benzene was the following:
CH
HC
6
1
2
CH
5
HC
or
CH
CH
4
3
This structure would be called cyclohexatriene using the IUPAC system for naming aliphatic hydrocarbons that we have studied previously. However,
the properties of benzene are very different than those of other double or triple bonded hydrocarbons. For example, benzene is a very stable molecule
while alkenes and alkynes are both very reactive.
In fact, benzene has 6 identical carbon-carbon bonds in its structure. Benzene can be thought of as a hybrid of two “resonance forms” of
cyclohexatriene:
Either of these structures is identified as benzene
way to represent benzene is a ring of 6 carbons with a
although neither is actually correct. Instead, a common
circle in the middle:
In other words, the electrons involved in the “double”
bonds or pi bonds are shared equally among all 6 carbons. These pi electrons
are said to be delocalized in this arrangement. Every carbon is sp2 hybridization state with one electron involved in pi bonding. This means that
benzene has a planar structure as shown in these models:
a) 6 half-filled p orbitals
b) π-bonding (delocatized electrons)
c) electron density diagram
Property
Characteristics of Typical Organic and Inorganic Compounds
Organic
Solubility in water
Melting Point
Boiling Point
Decomposition
Insoluble
Low
Low
Occurs easily when heated
Reaction with O2
Combustion (produces CO2 & H2O )
Inorganic
Soluble
High
High
Requires very high temperatures
No combustion
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Some Important Classes of Organic Compounds
Class
1
Characteristic Structural Features of Molecules
Hydrocarbons
Prefixes in naming:
Prefix No. of C’s Alkyl Grp
H
Y
D
R
O
G
E
N
meth1
eth2
prop3
but4
pent5
hex6
hept7
oct8
non9
dec10
undec- 11
methyl
ethyl
propyl
butyl
pentyl
hexyl
heptyl
octyl
nonyl
decyl
undecyl
Examples
Contain only carbon and hydrogen: May have carbon
chains or carbon rings. Subclasses according to presence
of multiple bonds
C C
|
|
|
|
C
C
|
|
− C− C−
1-a. Alkanes: all single bonds
Propane
CH3CH2 − CH3
CH2 = CH − CH3
1-b. Alkenes: at least one double bond
−C = C
Propylene
1-c. Alkynes: at least one triple bond
−C ≡ C−
propyne
1-d. Aromatic: at least one benzene
like ring system
CH ≡ C − CH3
methylbenzene
Note: For a corresponding prefix for a alkyl group, just
add –yl: e.g. meth- becomes methyl2
Organic Halides:
–X
−X
3a
O
Alcohols:
Hydroxyl group
– OH
R − X , Ar − X
-F fluoro, -Cl chloro, -Br bromo, -I iodo, -
Chloropropane
nitro
At least one –OH joined to a tetrahedral carbon that has 3
other single bonds (a alkyl group:
CH3CH2 CH2 − Cl
CH 3CH2 CH 2 − OH
Propanol
R, R' , R" ) R − OH : 10 : R − CH 2 − OH , 20 : R − C| H − OH ,
−
R'
R"
|
30 : R − C − OH
|
R'
3b
O
Phenols (antiseptics):
Hydroxyl group
– OH
OH bonded with a aryl (phenol) group: ∅
X − ∅ − OH , R − ∅ − OH
Phenol
4
O
=
Carboxylic Acids: O
Hydroxyl group +
||
Carbonyl group = - C – OH
Carboxylic group:
5
O
=
6
O
=
Acid Anhydride O
2 carbonyl group ||
7
O
=
8
O
=
9
O
−
10
O
=
N
−
O
||
−C − O − C −
||
Carbonyl group: − C − O −
Aldehydes:
O
Terminal
||
Carbonyl group : - C -H
Ketones:
O
Non-terminal
||
Carbonyl group: - - C Ethers:
2 alkyl group bonded to “O”
An "oxy"
Amides: (very weak bases)
O
||
Carbonyl group − C− NH2
+ Ammonium
||
||
||
R[ H ] − C − OH , Ar − C − OH
O||
Propanoic acid
CH 3 − CH 2 − C − OH
O||
O||
O||
Acetic anhydride CH3 − C − O − C − CH3
R− C −O− C − R
Ester (acid derivative):
O
O
O
O
O
O
O
||
||
ethanoate CH 3 − C − O − CH 3
||
R H − C − O − R' ,
Ar − C − O − R
O
Methyl
(methyl acetate)
O
O
||
||
||
R H − C − H , Ar − C − H
Propanal
O
O
O
O
||
||
CH3 − CH2 − C − H
||
||
R − C − R' , R − C − Ar , Ar − C − Ar '
Propanone (acetone) CH3 − C − CH3
R − O − R' , R − O − Ar , Ar − O − Ar
Methoxylethane
CH3OCH2 CH3
dimethyl ether
CH3OCH3
O H
O
H
||
||
|
|
O R"
||
|
R H − C − N − H , R H − C − N − R ' , R H − C− N − R' ,
O
||
Ar − C − NH2
Propanamide
O
H
||
|
CH 3CH 2 − C − N − H
5
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N
−
Amines: (weak bases)
H in ammonia ( NH 3 )
replaced with alkyl groups
Class
1
H
H
R"
|
|
|
R'
|
R − N − H , or R − N − R ' , or R − N − R ' ; Ar − N − R
Methylamine
Dimethylamine
Characteristic Structural Features of Molecules
Degree of Polarity
Contain only carbon and hydrogen: May have carbon
chains or carbon rings. Subclasses according to presence
of multiple bonds
1. non-polar
C C
H
Y
D
R
O
G
E
N
Propylamine
CH3CH2 CH2 NH2
|
|
|
|
C
C
|
|
− C− C−
1-a. Alkanes: all single bonds
1-b. Alkenes: at least one double bond
−C = C
1-c. Alkynes: at least one triple bond
−C ≡ C−
CH3 NH2
,
CH 3 NHCH 3
•
Insoluble in water
•
Low boiling & melting
points
•
Extreme flammable
•
Van der Waals force
1-d. Aromatic: at least one benzene
like ring system
Note: For a corresponding prefix for a alkyl group, just
add –yl: e.g. meth- becomes methyl2
Organic Halides:
–X
−X
3a
O
Alcohols:
Hydroxyl group
– OH
R − X , Ar − X
-F fluoro, -Cl chloro, -Br bromo, -I iodo, -
nitro
At least one –OH joined to a tetrahedral carbon that has 3
other single bonds (a alkyl group:
7. polar, & more polar than
alcohols
6. polar, & can form hydrogen
bond
R, R ' , R" ) R − OH : 10 : R − CH 2 − OH , 20 : R − C| H − OH ,
−
R'
R"
|
30 : R − C − OH
|
R'
3b
O
4
O
=
5
O
=
6
O
=
7
O
=
8
O
=
9
O
−
Phenols (antiseptics):
Hydroxyl group
– OH
Carboxylic Acids: O
Hydroxyl group +
||
Carbonyl group = - C – OH
Carboxylic group:
O
Acid Anhydride O
2 carbonyl group ||
||
−C − O − C −
OH bonded with a aryl (phenol) group: ∅
X − ∅ − OH , R − ∅ − OH
||
Carbonyl group: − C − O −
Aldehydes:
O
Terminal
||
Carbonyl group : - C -H
Ketones:
O
Non-terminal
||
Carbonyl group: - - C Ethers:
2 alkyl group bonded to “O”
||
||
O||
4. polar, but less polar than
alcohols
O||
R− C −O− C − R
Ester (acid derivative):
O
O
O
R[ H ] − C − OH , Ar − C − OH
O
O
||
||
R H − C − O − R' ,
Ar − C − O − R
O
O
||
||
R H − C − H , Ar − C − H
O
||
5. polar, but less polar than
alcohols
5. polar, but less polar than
alcohols
O
||
O
||
R − C − R' , R − C − Ar , Ar − C − Ar '
R − O − R' , R − O − Ar , Ar − O − Ar
3. less polar than carboxylic acids
(relatively non-polar), but more
polar than ethers
3. more polar than hydrocarbon &
less polar than alcohols; good
solvent
3. more polar than hydrocarbon &
less polar than alcohols; good
solvent
2. more polar than hydrocarbon;
Hydrogen bond is possible
6
10
O
=
N
−
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N
−
Amides: (very weak bases)
O
||
Carbonyl group − C− NH2
+ Ammonium
Amines: (weak bases)
H in ammonia ( NH 3 )
replaced with alkyl groups
O H
O
H
||
||
|
|
O R"
||
|
R H − C − N − H , R H − C − N − R ' , R H − C− N − R' ,
3. less polar than amines, but
comparable to esters
O
||
Ar − C − NH2
H
H
R"
|
|
|
R'
|
R − N − H , or R − N − R ' , or R − N − R ' ; Ar − N − R
5. polar, but less polar than
alcohols
PhysicalProperties of Organic Compounds
Additional Characteristics of Alcohols
• Alcohols are extremely flammable, and should be treated with caution.
• Most alcohols are poisonous. Methanol can cause blindness or death when consumed. Ethanol is consumed widely in moderate
quantities, but it causes impairment and/or death when consumed in excess.
Additional Characteristics of Carboxylic Acids
• Carboxylic acids often have unpleasant odours. For example, butanoic acid has the odour of stale sweat.
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• The−OH group in a carboxylic acid does not behave like the basic hydroxide ion, OH . Oxygen has a high electronegativity (attraction to
electrons) and there are two oxygen atoms in the carboxylic acid functional group. These electronegative oxygen atoms help to carry the
extra negative charge that is caused when a positive hydrogen atom dissociates. This is why the hydrogen atom in a carboxylic acid is
able to dissociate, and the carboxylic acid behaves like an acid.
−
• Figure below compares the melting and boiling points of a carboxylic acid with the melting and boiling points of other organic
compounds. As you can see, the melting and boiling points of the carboxylic acid are much higher than the melting and boiling points of
the other compounds. This is due to the exceptionally strong hydrogen bonding between carboxylic acid molecules.
Additional Characteristics of Esters
• Esters often have pleasant odours and tastes, so they are used to produce perfumes and artificial flavours. In fact, the characteristic tastes
and smells of many fruits come from esters.
Additional Characteristics of Aldehydes and Ketones
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• In general, aldehydes have a strong pungent smell, while ketones smell sweet. Aldehydes with higher molecular masses have a pleasant
smell. For example, cinnamaldehyde gives cinnamon its spicy smell. (See Figure 1.20.) Aldehydes and ketones are often used to make
perfumes. The rose ketones (shown in Figure 1.21) provide up to 90% of the characteristic rose odour. Perfumers mix organic
compounds, such as the rose ketones, to obtain distinctive and attractive scents.
• Since aldehydes and ketones are polar, they can act as polar solvents. Because of the non-polar hydrocarbon part of their molecules,
aldehydes and ketones can also act as solvents for non-polar compounds. For example, 2-propanone (common name: acetone) is an
important organic solvent in the chemical industry.
• Table 1.10 compares the boiling points of an alkane, an alcohol, and an aldehyde with the same number of carbon atoms. You can see
that the boiling point of an alcohol is much greater than the boiling point of an alkane or an aldehyde.
Additional Characteristics of Ethers
• Like alcohols, ethers are extremely flammable and should be used with caution.
Additional Characteristics of Amides
• An amide called acetaminophen is a main component of many painkillers.
• Urea, another common example of an amide, is made from the reaction between carbon dioxide gas, CO2, and ammonia, NH3 . Urea was
the first organic compound to be synthesized in a laboratory. It is found in the urine of many mammals, including humans, and it is used
as a fertilizer.
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Additional Characteristics of Amines
• Amines are found widely in nature. They are often toxic. Many amines that are produced by plants have medicinal properties.
• Amines with low molecular masses have a distinctive fishy smell. Also, many offensive odours of decay and decomposition are caused by amines. For
example, cadavarine, H2NCH2CH2CH2CH2CH2NH2 contributes to the odour of decaying flesh. This compound gets its common name from the word
"cadaver" meaning "dead body".
• Like ammonia, amines act as weak bases. Since amines are bases, adding an acid to an amine produces a salt. This explains why vinegar and lemon
juice (both acids) can be used to neutralize the fishy smell of seafood, which is caused by basic amines.
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Summary of Organic Compounds, Their Functions and Uses
Family
1-a. Alkanes
1-b. Alkenes
Structures & Features
Branched-chains
Cyclic
Structural isomers
Branched-chains
Cyclic
Geometric isomers
Vinyl carbons
Polymerization
1-c. Alkynes
1-d. Aromatics,
Heterocyclic, &
Fused-Ring
Aromatics
2. Organic
halides
3-a. Alcohols
3-a. Cyclic
alcohols
3-b Phenols
Benzene ring: orthoMetaPara-
Extremely
flammable
Flammable with
very high
temperature
Pleasant odors
Some toxic &
carcinogenic
Polyalcohols: -diol, -triol
Cyclic
Aromatic
Thiols
Toxic
Very flammable
Pleasant odors
Heterocyclic
Fused-ring
3-c. Thiols
4. Carboxylic
acids
Special
Characteristics
Extremely
flammable
(i) Dicarboxylic (-dioic)
(ii) Tricarboxylic acid of propane
Burns easily
Strong, unpleasant
odors
Some with
distinctive odors
Acids with 1 or more double bonds
Keto carboxylic acids (those
with a carbonyl group attached)
6. Esters
(organic salts)
7. Aldehydes
8. Ketones
Thioesters
Polymerization: ester linkages
Acid anhydrides
Phosphate esters
Hemiacetals & acetals
Hemiacetals & acetals
9. Amides
(organic salts)
Amide linkage (peptide bond)
Heterocyclic
Polymerization
10. Amines
Diamines
(organic bases) Heterocyclic
11. Ethers &
Epoxides
Cyclic
Functions & Uses
•
•
•
•
•
•
•
•
•
•
•
Gas, gasoline, fuels, and oil
Pheromones
Petroleum as raw materials for plastics
Fuel
Ethene stimulates fruit ripening
Beta-carotene (Vitamin A)
Pheromones
Insecticides
Polymerization to produce plastics
Welding
Synthesis of alkenes and alkanes
• Good solvent for numerous substances
• Compounds give distinctive aromas to cloves, vanilla beans, and almonds
• Compounds containing rings similar to benzene include nucleic acids (DNA), several
vitamins, hormones, & pharmaceuticals
• Use as intermediates in the synthesis of other organic compounds for ease of substituting
a halogen
• Refrigerant & aerosol propellant (CFCs being replaced by (HFCs)
• Anesthetic
• Gasoline additive
• Freezing agent
• Dry cleaning solvent (tetrachloromethane commonly known as tetrachloride now replaced
by dichloromethane (methylene chloride))
• Pesticides including DDT (now banned) and chlordane
• Good solvent for polar & nonpolar compounds
• Rubbing alcohol
• Antifreeze
• Lotions, soap, shaving cream, glycerin suppositories
• Flavoring, skin lotion, throat lozenges
• Cholesterol
• Antiseptic and disinfectant
• Indicator for acid-base titration
• Preparation of plastics, drugs, dyes, & weed killers
• Some exert profound pyschological effects
• Epinephrine & hydoquinone
• Some oxidized in fruits & vegetables
• Addition to gas for detection of gas leakage
• Weak acids in citrus fruits, milk, yogurt
• Acetic acid, first isolated from vinegar, used to produce other chemicals & to prepare foods
e.g. pickles, mayonnaise, salad dressing.
• Carboxylic salts as food preservatives, soaps
Most pleasant
odors of fruits &
flowers
• Flavoring in processed foods
• Scents in cosmetics and perfumes
Appealing tastes
and fragrant
odors
•
•
•
•
•
Appealing tastes
and fragrant
odors
Components of
proteins
Unpleasant odors
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
Antiseptic and disinfectant
Synthesis of resins and dyes, and preservatives
Formaldehyde trimer to fumigate rooms against pests
Acetaldehyde trimer for hypnotic drugs
Used as flavorings in food and candy (such as vanilla flavoring in ice cream, and
cinnamon) and as fragrance in inhalants and perfumes
Good solvent for both polar & nonpolar substances
Important in functional of human body
Used as flavorings in food and candy and as fragrance in inhalants and perfumes
Good solvent for both polar & nonpolar substances (acetone, a volatile liquid, & its vapor
is quite flammable, is a common solvent, a primary component in fingernail polish remover)
Important in functional of human body (sex hormones, & cortisone)
Pheromones
Amide group occurs in proteins & peptide bonds form backbone of all protein molecules
Present in synthetic fibers such as nylon
Nicotine, coniine, piperine, cocaine, caffeine
Ptomaines
Amino group present in DNA, vitamins, & anesthetic drug (Novocain)
Basis of addictive compounds such as nicotine, cocaine, and amphetamines
Epinephrine & hydoquinone
Solvent for fats & oils (organic compounds)
Anesthetics (in19th century)
Sterilization of medical equipment
A third ether, one of the methyl butyl ethers, is used in gasoline to reduce pollution and
improve engine efficiency