Transcript Chapter 1 - chemistry

Chapter 23
Functional Groups
Functional Groups
Most organic chemistry involves substituents, which are
groups attached to hydrocarbon chains.
The substituents of organic molecules often contain oxygen,
nitrogen, sulfur and phosphorus.
They are called functional groups because they are the
chemically functional parts of the molecules.
Organic compounds can be classified according to their
functional groups.
They symbol R represents any carbon chains or rings
attached to the functional group.
 And  bonds of alkenes and alkynes are chemically
reactive and are also considered functional groups.
Halogen Substituents
Halocarbons in which a halogen is attached to a carbon of
an aliphatic chain are called alkyl halides.
The number of carbon atoms attached to the alkyl group
determines whether the carbon is primary, secondary, or
tertiary.
Halocarbons in which a halogen is attached to a carbon of
an arene (aromatic hydrocarbon) ring are called aryl
halides.
The attractions between halocarbon molecules are primarily
the result of weak van der Waals interactions called
dispersion forces.
The attractions increase with the degree of halogen
substitution.
Halogen Substituents
The more highly halogenated organic compounds have
higher boiling points.
Very few halocarbons are found in nature, but they can be
readily prepared and used for many purposes.
Hydrofluorocarbons are used as refrigerants in automobile
air conditioning systems.
Halothan (2-bromo-2-chloro-1,1,1,-trifluoroethane) is used
and an anesthetic.
Effect of Structure on Boiling Point
CH3CH2CH3
CH3CH2F
CH3CH2OH
Molecular
weight
44
48
46
Boiling
point, °C
-42
-32
+78
Effect of Structure on Boiling Point
CH3CH2CH3
Molecular
weight
44
Intermolecular forces
are weak.
Boiling
point, °C
-42
Only intermolecular
forces are induced
dipole-induced dipole
attractions.
Effect of Structure on Boiling Point
CH3CH2F
Molecular
weight
48
Boiling
point, °C
-32
Dipole
moment, D
1.9
A polar molecule;
therefore dipole-dipole
and dipole-induced
dipole forces contribute
to intermolecular
attractions.
Effect of Structure on Boiling Point
CH3CH2OH
Molecular
weight
46
Boiling
point, °C
+78
Dipole
moment, D
1.7
Highest boiling point;
strongest intermolecular
attractive forces.
Hydrogen bonding is
stronger than other
dipole-dipole attractions.
Halogen Substituents
Chloromethane
(methyl chloride)
Chlorobenzene
(phenyl chloride)
Nomenclature of Alkyl Halides
Name the alkyl group and the halogen as
separate words (alkyl + halide)
CH3F
CH3CH2CH2CH2CH2Cl
Methyl fluoride
Pentyl chloride
CH3CH2CHCH2CH2CH3
Br
1-Ethylbutyl bromide
H
I
Cyclohexyl iodide
Nomenclature of Alkyl Halides
• Name as halo-substituted alkanes.
• Number the longest chain containing the
halogen in the direction that gives the lowest
number to the substituted carbon.
CH3CH2CH2CH2CH2F
1-Fluoropentane
CH3CH2CHCH2CH3
I
3-Iodopentane
CH3CHCH2CH2CH3
Br
2-Bromopentane
Nomenclature of Alkyl Halides
Cl
CH3
CH3
Cl
• Halogen and alkyl groups
are of equal rank when
it comes to numbering
the chain.
• Number the chain in the
direction that gives the
lowest number to the
group (halogen or alkyl)
that appears first.
Nomenclature of Alkyl Halides
Cl
5-Chloro-2-methylheptane
CH3
CH3
2-Chloro-5-methylheptane
Cl
Nomenclature of Alkyl Halides
1,2 or 1,3 or 1,4-dichlorobenzene
chloromethylbenzene
chlorobenzene
benzyl chloride
Aryl Halides
Classification
• Alcohols and alkyl halides are classified as
primary
secondary
tertiary
according to their "degree of substitution."
• Degree of substitution is determined by counting
the number of carbon atoms directly attached to
the carbon that bears the halogen or hydroxyl group.
Classification
H
CH3CH2CH2CH2CH2F
OH
primary alkyl halide
secondary alcohol
CH3
CH3CHCH2CH2CH3
Br
secondary alkyl halide
CH3CCH2CH2CH3
OH
tertiary alcohol
Structural formula
Name
CH3-
Methyl-
CH3CH2-
Ethyl-
CH3CH2CH2-
propyl- or n-propyl
(CH3)2CH-
Isopropyl-
CH3CH2CH2CH2-
butyl- or n-butyl
CH3CHCH2CH3
sec-butyl- or s-butyl
(CH3)2CHCH2-
isobutyl
(CH3)3C-
tert-butyl or t-butyl
Substitution Reactions
Organic reactions often proceed more slowly than inorganic
reactions.
Organic reactions commonly involve the breaking of
relatively strong covalent bonds. Catalysts are often
needed.
Many organic reactions are complex, often producing a
mixture of products.
The desired product must then be separated by distillation,
crystallization, or other means.
A common type of organic reaction is a substitution
reaction, in which an atom or a group of atoms replaces
another atom or group of atoms.
Substitution Reactions
A halogen can replace a hydrogen atom on an alkane to
produce a halocarbon.
CH4
+
Cl2

CH3Cl +
HCl
Sunlight or another source of ultraviolet radiation usually
serves as a catalyst.
Even under controlled conditions, this simple halogenation
reaction produces a mixture of mono-, di-, tri-, and
tetrachloromethanes.
Substitution Reactions
Iron compounds are often used as catalysts for aromatic
substitution reactions.
Halogens on carbon chains are readily displace by
hydroxide ions to produce an alcohol and a salt.
CH3I + KOH 
CH3OH + KI
Substitution Reactions
Iron compounds are often used as catalysts for aromatic
substitution reactions.
Halogens on carbon chains are readily displace by
hydroxide ions to produce an alcohol and a salt.
CH3I + KOH 
CH3OH + KI
Fluoro groups are not easily displaced. Thus, fluorocarbons
are seldom, if ever, used to make alcohols.
Questions
How are organic compounds classified?
According to their functional groups
What is a halocarbon?
Class of organic compounds containing covalently bonded
fluorine, chlorine, bromine, or iodine.
How can a halocarbon be prepared?
By reacting an alkane with a halogen, catalyzed by UV light.
Questions
Identify the functional group in each structure
Isopropyl chloride
hydroxyl
CH3 – CH2 – NH2
amino
CH3 – CH2 – CH2 – Br
Halogen
CH3 – CH2 – O – CH2 – CH3
ether
Questions
Give the structural formula for the compound
Isopropyl chloride
CH3
|
CH3 – C – Cl
|
H
Questions
Give the structural formula for the compound
1-iodo-2,2-dimethylpentane
CH3
|
I – CH2 – C – CH2 – CH2 –CH3
|
CH3
Questions
Give the structural formula for the compound
P-bromotoluene
Write the names of all possible dichloropropanes that could
form from the chlorination of propane.
1,1,-dichloropropane
1,2-dichloropropane
2,2-dichloropropane
1,3-dichloropropane
Questions
Write the structural formulas for ethene, ethyl chloride, and
ethanol.
Identify their functional groups.
Choose two of the compounds to illustrate a substitution
reaction.
Explain the terms primary, secondary and tertiary.
End of Section 23.1
Alcohols
The –OH functional group in alcohols is called a hydroxyl
group.
Aliphatic alcohols can be classified into structural categories
according to the number of R groups attached to the
carbon with the hydroxyl group.
Primary
Secondary
Tertiary
Naming Alcohols - IUPAC
When using the IUPAC system to name continuous-chain
substituted alcohols, drop the –e ending of the parent
alkane name and add the ending –ol.
The parent alkane is the longest continuous chain of C that
includes the C attached to the hydroxyl group.
In numbering the longest continuous chain, the position of
the hydroxyl group is given the lowest possible number.
Alcohols containing two, three, and four – OH substituents
are name diols, triols, and tetrols, respectively..
Common Names - Alcohol
Common names of aliphatic alcohols are written in the
same way as those of the halocarbons.
The alkyl group ethyl, for example, is named and followed
by the word alcohol, as in ethyl alcohol.
Compounds with more than one – OH substituent are called
glycols.
Methanol
Methyl alcohol
Ethanol
Ethyl alcohol
2-propanol
Propyl alcohol
Naming Alcohols
2-methyl-2-propanol
tert-butyl alcohol
2-propanol
isopropyl alcohol
2-butanol
sec-butyl alcohol
2-methyl-1-propanol
isobutyl alcohol
Naming Alcohols
1,2-ethanediol
ethylene glycol
2-propanol
isopropyl alcohol
1,2,3-propanetriol
glycerol (glycerin)
2-methyl-1-propanol
isobutyl alcohol
Properties of Alcohols
Alcohols are capable of intermolecular hydrogen bonding.
Therefore, they boil at higher temperatures than alkanes
and halocarbons containing comparable numbers of
atoms.
Because alcohols are derivatives of water, (the hydroxyl
group is part of a water molecule) they are somewhat
soluble.
Alcohols of up to four carbons are soluble in water in all
proportions.
The solubility of alcohols with four or more carbons in the
chain is usually much lower.
Properties of Alcohols
Alcohols consist of two parts: the carbon chain and the
hydroxyl group.
The carbon chain is nonpolar and is not attracted to water.
The hydroxyl group is polar and strongly interacts with
water through hydrogen bonding.
For alcohols of up to four carbons, the polarity of the
hydroxyl group is more significant than the nonpolarity of
the carbon chain. These alcohols are soluble in water.
As the number of carbon atoms increases above four, the
nonpolarity of the chain becomes more significant, and
the solubility decreases.
Properties of Alcohols
Many aliphatic alcohols are used in laboratories, clinics and
industry as rubbing alcohol, antiseptic and as a base for
perfumes, creams, lotions and other cosmetics.
Ethylene glycol (1,2-ethanediol) is the principal ingredient of
certain antifreezes.
Ethyl alcohol is called grain alcohol and is an important
industrial chemical.
Most ethanol is still produced by yeast fermentation of
sugar. Fermentation is the production of ethanol from
sugars by the action of yeast or bacteria.
Properties of Alcohols
Ethanol is the intoxication substance in alcoholic beverages.
It is a depressant and can be fatal if taken in large doses
at once.
The ethanol used in industrial application is denatured.
Denatured alcohol is ethanol with an added substance to
make it toxic.
The added substance is often methyl alcohol, which is
sometimes called wood alcohol because it used to be
prepared by the distillation of wood.
Wood alcohol is extremely toxic. As little as 10 mL has been
reported to cause permanent blindness and as little as 30
mL to can cause death.
Addition Reactions
The carbon-carbon single bonds in alkanes are not easy to
break.
In alkenes one of the bonds in the double bond is
somewhat weaker and is easier to break than a carboncarbon single bond.
It is sometimes possible for a compound of general
structure X-Y to add to a double bond.
In an addition reaction, a substance is added at the
double or triple bond of an alkene or alkyne.
Addition Reactions
Addition reactions of alkenes are an important method of
introducing new functional groups into organic molecules.
In alkenes one of the bonds in the double bond is
somewhat weaker and is easier to break than a carboncarbon single bond.
It is sometimes possible for a compound of general
structure X-Y to add to a double bond.
In an addition reaction, a substance is added at the
double or triple bond of an alkene or alkyne.
Addition Reactions
The addition of water to an alkene is a hydration reaction.
Hydration reactions usually occur when the alkene and
water are heated to about 100ºC in the presence of a
trace of strong acid. (The acid usually HCl or H2SO4,
serves as a catalyst for the reaction.)
When the reagent is a halogen, a disubstituted halocarbon
is produced.
Addition Reactions
The addition of bromine to carbon-carbon multiple bonds is
often used as a chemical test for unsaturation in an
organic molecule.
Bromine has a brownish-orange color, but most organic
compounds of bromine are colorless.
The loss of the orange color is a positive test for
unsaturation. If the orange remains, the sample is
completely saturated.
Hydrogenation Reactions
Hydrogen halides can also be added to a double bond. The
product is called a monosubstituted halocarbon because
it only has one substituent.
The addition of hydrogen to a carbon-carbon double bond
to produce an alkane is called a hydrogenation
reaction.
Hydrogenation reactions usually require a catalyst.
Platinum or paladium are often used.
The manufacture of margarine from unsaturated vegetable
oils is a common application of a hydrogenation reaction.
Hydrogenation Reactions
The hydrogenation of a double bond is a reduction reaction.
Ethene is reduced to ethane.
Under normal conditions, benzene resists hydrogenation. It
also resists the addition of a halogen or a hydrogen
halide.
Under condition of high temperature and high pressures of
hydrogen, and with certain catalysts, three molecules of
hydrogen gas can reduce one molecule of benzene to
form one molecule of cyclohexane.
Ethers
An ether is a compound in which oxygen is bonded to two
carbon groups.
The general structure of an ether is R – O – R.
The alkyl groups attached to the ether linkage are named in
alphabetical order and are followed by the word ether.
Some ethers are non-symmetric, because the R groups
attached to the ether oxygen are different.
H H H
|
| |
H-C-O-C-C-H
|
| |
H HH
methyl ethyl ether
Ethers
When both R groups are the same the ether is symmetric.
Symmetric ethers are named using the prefix di-.
Diethyl ether
Ethers
tert-butyl isopropyl ether
1,4-dioxahexylbenzene
Diethyl ether
Ethers
Diethyl ether was the first reliable general anesthetic.
Diethyl ether has been replaced by other anesthetics such
as halothan because it is highly flammable and often
causes nausea.
Ethers usually have lower boiling points than alcohols of
comparable molar mass.
They have higher boiling points than comparable
hydrocarbons and halocarbons.
Ethers are more soluble in water than hydrocarbons and
halocarbons, but less soluble than alcohols. This is
because the O in an ether is a hydrogen acceptor.
Ethers form more hydrogen bonds than hydrocarbons and
halocarbons, but fewer than alcohols.
Questions
How are alcohols classified and named?
Alcohols are classified as primary, secondary, or tertiary.
They are named by dropping the –e ending of the parent
alkane name and adding the ending -0l
How does the solubility of alcohols vary with the length of
the carbon chains?
Alcohols are soluble in water when the carbon chain of the
alcohol contains four or fewer carbons. The solubility of
longer chain alcohols is much lower.
How can functional groups be introduced into organic
molecules?
By addition or substitution reactions
End of Section 23.2
End of Chapter 23