Transcript functional group

Organic Chemistry
CHEMISTRY 30
Intro to Hydrocarbons

Hydrocarbon: an organic compound that contains only
carbon and hydrogen.

E.g. methane

Recall from our last unit that carbon wants to make four
bonds.

We can represent hydrocarbons in different ways:
Lewis Structure
Properties of Hydrocarbons

Hydrocarbons with low masses tend to be gases or liquids that boil
at a low temperature (due to low IMFs)

Recall the general rule “like dissolves like.” Because of this,
hydrocarbons are insoluble in polar compounds. This explains why
oil and water do not mix!
Alkanes

An alkane is a hydrocarbon in which there are only single covalent bonds.

Each carbon-carbon bond is a single covalent bond, and every other
bond is a carbon-hydrogen bond.

Alkanes have the general formula CnH2n+2

They end with “ane” Ex: C3H8 = Propane
Alkanes

Alkanes are named by counting the number of carbons, and by using the
corresponding prefix for that number. Then you add “-ane” to represent
an alkane. You will need to memorize the names of the first ten alkanes.
Straight-Chain Alkanes

Ethane is the simplest straight-chain alkane, which is an alkane that
contains any number of carbon atoms, one after the other.

To draw the structural formula, draw each carbon connected by a bond,
and complete each carbon’s octet with hydrogens.
Stop and Check!

Draw complete structural formulas for the straight-chain alkanes that have:

Three carbon atoms

Four carbon atoms

Five carbon atoms

Name each of the above structures.

How many single bonds are there in a propane molecule?
Branched-Chain Alkanes

Carbons can connect in branched chains.

Substituent: an atom (or group of atoms) that can take the place of a
hydrogen atom on a parent hydrocarbon molecule.

The parent alkane is the longest continuous carbon chain. All other carbon
atoms or groups of atoms are called substituents.

The parent alkane of the above compound is hexane (six carbons).
Branched-Chain Alkanes

A hydrocarbon substituent that is derived from an alkane is called an alkyl
group. Think of an alkyl group as an alkane with one of the hydrogens
removed.

An alkyl group can be one or more carbons long.

Name these groups by removing the –ane ending from the parents
hydrocarbon name and adding –yl.

The three smallest alkyl groups are the methyl group (-CH3); the ethyl group
(-CH2CH3), and the propyl group (-CH2CH2CH3)
Branched-Chain Alkanes

When a substituent alkyl group is attached to a straight-chain hydrocarbon,
branches are formed. An alkane with one or more alkyl groups is called a
branched-chain alkane.

Each carbon in an organic molecule can be characterized as a primary,
secondary, tertiary, or quaternary carbon.

Primary: 1 carbon attached to it

Secondary: 2 carbons attached to it

Tertiary: 3 carbons attached to it

Quaternary: 4 carbons attached to it
Branched-Chain Alkanes
Naming Branched-Chain Alkanes

IUPAC (International Union of Practical and Applied Chemists) naming system (like everything
else we know how to name!)

We will use the following molecule:
Naming Branched-Chain Alkanes


Find the longest continuous chain of carbons in the molecule. This
is considered the parent hydrocarbon.

2
5
1
6
Step 2:


3
The longest chain has six carbons, therefore the parent
hydrocarbon is hexane.

4
Step 1:
Number the carbons in the main chain in sequence. Start at the end that will give the substituent groups
attached to it the smallest numbers.
Step 3:

Add numbers to the names of the substituent groups to identify their positions on the chain. These
numbers become prefixes to the name of the substituent group .

The substituents and positions are 2-methyl and 4-methyl.
Naming Branched-Chain Alkanes

Step 4:

Use prefixes to indicate the appearance of the same group more
4
than once in the structural formula. Common prefixes are di- (two),
3
tri- (three), and tetra- (four).


The two methyl groups are combined as 2,4-dimethyl.
Step 5:

List the names of alkyl substituents in alphabetical order.

For the purposes of alphabetizing, ignore the prefixes di-, tri-, and so on.

The 2,4-dimethyl group is our only substituent group, so we name it first.
5
6
2
1
Naming Branched-Chain Alkanes

Step 6:

Combine all the parts and use proper punctuation. Write the entire name
without any spaces.

Use commas to separate numbers and use hyphens to separate numbers and
words.

Our molecule becomes 2,4-dimethylhexane.
Naming Branched-Chain Alkanes

Name the following alkanes:
4-ethyl-2,4-dimethylheptane
4,4,5-tripropyloctane
2,2,3-trimethyl-3-ethylheptane
Drawing Branched-Chain Alkanes

Draw the structural formula for the following molecules:

octane

2,2,4-trimethylpentane

3-methylhexane

3-ethyl-3,4-dimethyloctane
Unsaturated Hydrocarbons

Saturated Compound: an organic compound that only contains single bonds.

Unsaturated Compound: an organic compound that contains double or triple
carbon-carbon bonds.

An alkene is a hydrocarbon that contains one or more carbon-carbon double
bonds.
Alkenes

Ethene is the simplest alkene. It is often called by the common name ethylene.

To name an alkene by the IUPAC system, find the longest
chain in the molecule that contains the double bond. This
chain is the parent alkene.

The parent alkene is named just like the alkane with the same number of carbons,
plus the ending –ene. The chain is numbered so the carbon atoms with the double
bond have the lowest possible numbers.

Name the substituents the same way you would for an alkane.
Alkenes

E.g. name the following alkenes:
propene
1-butene
2-butene
4-methyl-2-pentene
Alkynes

A hydrocarbon that contains one or more carbon-carbon triple bonds is
called an alkyne. Like alkenes, alkynes are unsaturated hydrocarbons.

The simplest alkyne is ethyne (C2H2), which has the common name acetylene.

They are named the same way as alkenes and alkanes.
1-propyne
4-methyl-2-pentyne
Isomers

Structures of some hydrocarbons differ only by positions of substituents or of multiple bonds.
Isobutane is also called
2-methylpropane

Compounds that have the same molecular formula but different molecular structures are called
isomers.
Constitutional Isomers

Butane and 2-methylpropane are specifically called constitutional isomers because they
have the same molecular formula but are joined together differently.

What are some other constitutional isomers?

Constitutional isomers differ in physical properties such as boiling point and melting point.
They also have different chemical reactivities.

In general, the more highly branched the hydrocarbon is, the lower the boiling point of the
isomer will be compared with less branched isomers.

n-butane boiling point: -1.0 degrees Celcius; isobutane’s boiling point: -11.7 degrees Celcius
Isomers as Substituent Groups

Alkyl groups can be organized in branched chains just like the parent hydrocarbon can.

A propyl group can either be n-propyl (n for normal) or iso-propyl (iso for isomer):
n-propyl group
iso-propyl group
Isomers as Substituent Groups

Butyl groups work the same way, as shown:

sec- and tert- represent the degree of the first carbon in the group (the one bonded to
the parent hydrocarbon)
Stereoisomers

Remember that molecules are 3-D structures. This means that molecules with the same
molecular formula and with atoms joined in exactly the same order may still be isomers.

Stereoisomers are molecules in which the atoms are joined in the same order, but the positions
of the atoms in space are different.

The two types of stereoisomers are cis-trans isomers and enantiomers. We will be focusing our
study on cis-trans isomers rather than enantiomers.
Cis-Trans Isomers

A double bond between two carbons prevents other atoms in the molecule from rotating, or
spinning, with respect to one another. Because of this lack of rotation, groups on either side of
the double bond will be ‘stuck’ in specific orientations.

Cis-trans isomers, aka geometric isomers, have atoms joined in the same order but with a
different spatial orientation.

Cis-trans isomerism occurs most frequently in molecules with double bonds.
Cis-Trans Isomers

Look at the models of 2-butene:

In the cis configuration, similar groups are on
the same side of the double bond.

In the trans configuration, similar groups are
on the opposite sides of the double bond.

Cis-trans isomers have different chemical and
physical properties.
Hydrocarbon Rings

Not all hydrocarbons are straight chains or branched chains. In some hydrocarbon
compounds, the carbon chain is in the form of a ring.

A compound that contains a hydrocarbon ring is called a cyclic hydrocarbon. Many
molecules found in nature contain cyclic hydrocarbons. Rings with 5 and 6 carbons are the
most abundant.

Cyclic hydrocarbons can be either saturated or unsaturated. A cyclic hydrocarbon that
contains only single bonds (and therefore is saturated), is called a cycloalkane.
Cyclic Hydrocarbons

To name a cycloalkane, count the number of carbons in the ring and assign the
corresponding alkane name. Then simply add the prefix cyclo- to the alkane name.
Cyclic Hydrocarbons

Substituents are named just as they would be for an alkane.
1-ethyl-3-methylcyclohexane
2-methyl-1-propylcyclopentane
Aromatic Hydrocarbons

There is a class of unsaturated cyclic hydrocarbons that are responsible for the aromas of
spices such as vanilla, cinnamon, cloves, and ginger. These were classified as aromatic
compounds because of their pleasant aromas. However, not all aromatic compounds
even have a smell at all.

An aromatic compound is defined as an organic compound that contains a benzene
ring, or another ring in which the bonding is like that of benzene.

Any compound not classified as aromatic is called an aliphatic compound. All of the nonaromatic compounds we’ve studied so far are aliphatic.
Aromatic Hydrocarbons

Benzene: a six-carbon ring with one hydrogen attached at each carbon.

This arrangement leaves one electron from each carbon free to participate in a double
bond. Benzene is drawn as such:
Aromatic Hydrocarbons

Benzene can be drawn using resonance structures:

The bonding electrons between carbon atoms are
shared evenly around the ring.

Benzene is often drawn with a circle inside the
hexagonal structure to demonstrate that those
electrons are shared evenly.

Benzene and other molecule that exhibit resonance
are more stable than similar molecules that do not
exhibit resonance, making it less reactive.
Naming Aromatic Compounds

Compounds containing substituent groups
 When the benzene group is a substituent, the
attached to a benzene ring are named using
C6H5 group is called a phenyl group.
benzene as the parent hydrocarbon.
methylbenzene
ethylbenzene
3-phenylhexane
Stop and Reflect

How does the length of a hydrocarbon chain affect its properties? How does the degree
to which it is branched affect its properties? Review with a partner.
Functional Groups

Essential Question: What effect does a functional group have on an organic compound?

How do you think the properties of an alkane might be affected if you replaced one of its
hydrogen atoms with a halogen atom?
Functional Groups


Key Questions:

How are organic compounds classified?

What is the general formula of a halocarbon?

How are substitution reactions used in organic chemistry?
Most organic chemistry involves substituents, often containing oxygen, nitrogen, sulfur, and/or
phosphorus. They are called functional groups because they are the chemically functional
parts of the molecules.

A functional group is a specific arrangement of atoms that is capable of characteristic
chemical reactions. Most organic chemistry involves the functional groups of organic
molecules.
Functional Groups

Organic compounds are classified based according to their functional groups.

General Formulas of Functional Groups, and the ‘R’ Group:

Refer to the table given to you as new functional groups are introduced. In each general
structure listed, the symbol ‘R’ represents any carbon chains or rings attached to the
functional group. In some cases, R can be a hydrogen atom. When more than one R
group is shown in the structural formula, the groups do not need to be the same.
Halocarbons

A halocarbon is an organic compound that contains at least one covalently bonded
fluorine, chlorine, bromine, or iodine atom (halogens).

The general formula for a halocarbon is RX, where X is a halogen substituent.

Rules for naming halocarbons are based on the name of the parent hydrocarbon, with
the halogens named as substituents.
IUPAC: chloromethane
Common: methyl chloride
IUPAC: chloroethene
Common: vinyl chloride
IUPAC: chlorobenzene
Common: phenyl chloride
Naming Halocarbons

Naming a halocarbon is similar to naming a hydrocarbon.

You need to specify the name of the halogen, the number of halogens (if
greater than one), and their positions on the hydrocarbon.

Halogens written as prefixes such as chloro-, fluoro-, bromo-, etc.
Name the Following

CH3CHFCH3

CCl2HCH2CH2CH2Cl

CCl2F2

CH3Br

CH3CH2CHICH3

Cl2C=CCl2

CCl4
Draw the Following Halocarbons

2-chloropentane

1,1,1-trichloroethane

3-fluoropropene

2,4-dibromohexane

1,2-diiodobutane
Halocarbons: Substitution Reactions

A halogen atom can replace a hydrogen atom on an alkane to produce a halocarbon.
The symbol X stands for a halogen in this generalized equation:
R --- H
+
alkane


X2
halogen
R --- X
+
halocarbon
HX
Hydrogen halide
From the generalized equation, you can write a specific one. This type of reaction is
called halogenation because it introduces a halogen atom into the molecule. Sunlight
usually serves as a catalyst.
CH4
+ Cl2

CH3Cl
+
HCl
Halocarbons: Substitution Reactions

Even under controlled conditions, this simple substitution produces a mixture of mono-, di-,
tri-, and tetrachloromethanes.

Halogenation of benzene in the presence of a catalyst causes the substitution of a
hydrogen atom on the ring. Iron compounds are often used as catalysts for substitution
reactions in aromatic compounds.
Halocarbons: Substitution Reactions

Halocarbons can be converted to other types of compounds by substitution reactions.
For example, hydroxide ions can displace halogen atoms to form an alcohol.

Fluorine is one exception. Since fluoro groups are not easily displaced, they are seldom used to
prepare alcohols.

Chemists usually use aqueous solutions of sodium hydroxide or potassium hydroxide.

E.g.:
CH3CH2Br(l) + NaOH(aq)  CH3CH2OH(l) +

NaBr(aq)
Halocarbons can be converted to other halocarbons, amines, or ethers by similar
substitution reactions.
Halocarbon Reactions

Unsaturated Hydrocarbons
Like hydrogen, halogens break the double bond and add to the
molecule in two places:
H2C=CH2 + F2  CH2FCH2F
name the product!
This is called an addition reaction.
Substitution or Addition?

CH4

C2H4

C3H4

C4H8

C5H12

C6H10

C6H14
Halocarbon Uses

Halocarbons are not naturally occurring

Their most important use is to build large organic molecules – their ability to
substitute for hydrogen is matched by their ability to be removed!

Many industrial uses of halocarbons have been limited because of their
toxicity, but they are still widely used.
Stop and Check!
1.
Review: How are organic compounds classified?
2.
Identify: What is the general formula of a halocarbon?
3.
Explain: Why are substitution reactions useful in organic chemistry?
4.
Draw:
1.
1-chloro-2-methylpropane
2.
1-iodo-2,2-dimethylpentane
3.
bromoethane
4.
2-bromo-2-chloro-1,1,1-trifluoroethane
Alcohols

An alcohol is an organic compound with an –OH group. The general formula is ROH.

The –OH functional groups is called a hydroxyl group, sometimes called a hydroxy group.
Due to VSEPR, hydroxyl groups have a bent shape.
Alcohols

To name aliphatic alcohols using IUPAC, drop the –e ending of the parent hydrocarbon and add
the ending –ol.

In numbering the parent hydrocarbon, the hydroxyl group is given the lowest possible number.

Some alcohols have more than one hydroxyl group. To name these alcohols, simply add the
ending –diol or –triol, to the parent hydrocarbon name.

E.g. 1,2,3-propanetriol:
Alcohols

When the hydroxyl group is attached directly to an aromatic ring, the compound is called
a phenol. To assign the IUPAC name, phenol is used as the parent hydrocarbon.

E.g. 2-methylphenol:
Alcohols

More examples:
ethanol
2-propanol
1,2-butanediol
Properties of Alcohols

Alcohols undergo hydrogen bonding, which results in a higher boiling point than alkanes
and halocarbons containing a comparable number of hydrogens.

Alcohols are somewhat soluble in water, being more soluble when the carbon chain is
shorter. Why do you think this is the case?
Uses of Alcohols

Alcohols have many common and industrial uses, including:

2-propanol is better known as rubbing alcohol, an antiseptic

1,2,3-propanetriol is very soluble in water, and thus is used as a moistening agent in cosmetics,
foods, and pharmaceuticals

Some antifreezes use 1,2-ethanediol as the main ingredient, due to its high boiling point

Ethanol is an important industrial chemical, which is produced by fermentation.

The ethanol in alcoholic beverages is generally produced by fermentation. It acts as a depressant
to the nervous system.

Methanol is extremely toxic – as little as 10 mL has been known to cause blindness, and 30 mL has
been known to cause death.
Addition Reactions

The carbon-carbon double bonds in alkanes are not easy to break. In an alkene, however,
the double bond is somewhat weaker and is easier to break than a single bond.

In an addition reaction, a substance is added at the double or triple bond of an alkene or
alkyne.

In the general addition reaction shown below, X and Y represent the two parts of the
reagent that are added to the alkene:
Addition Reactions – Hydration

Recall halogenation – the addition of a halogen to an alkene or alkyne. The addition of
water to an alkene is called hydration. It results in the formation of an alcohol.

This reaction takes place when the alkene and water are heated in the presence of a
strong acid.
Addition Reactions – Hydrogenation

The third type of addition reaction is called hydrogenation. Hydrogenation is the addition of
hydrogen to produce an alkane.

A platinum (Pt) or palladium (Pd) catalyst is often used:
Other Functional Groups

Aside from halocarbons and alcohols, there are numerous other types of functional groups. You
will be expected to recognize these functional groups (practice by using your table).

We will learn about:

Ethers

Amines

Carbonyl Compounds

Aldehydes

Ketones

Carboxylic Acids

Esters
Ethers

An ether is an organic compound in which oxygen is bonded to two carbon groups.

It is just like an alcohol, with another “R” group instead of a hydrogen.

The general formula of an ether is ROR, where both groups do not need to be the same:
Properties and Uses of Ethers

Diethyl ether was the first general anesthetic. However, since it is highly flammable and
often causes nausea, it eventually was replaced.

Ethers usually have lower boiling points than alcohols or comparable hydrocarbons and
halocarbons. Unlike alcohols, ethers are not capable of forming hydrogen bonds.
Amines

An amine is an organic compound in which nitrogen is bonded to a carbon group. Amines
are similar to ammonia (NH3). When one, two, or three of the hydrogens in ammonia are
replaced by carbon groups, the compound is classified as an amine.

Essentially, nitrogen-containing organic compounds are classified as amines.

The general formula of an amine is RNH2, R2NH, or R3N.
N
R
H
N
H
R
R’
N
H
R
R’ R’’
Properties of Amines

Like alcohols, amines form hydrogen bonds. Because nitrogen is less
electronegative than oxygen, the hydrogen bonds in amines are
not as strong as those of alcohols.

As a result, amines have lower boiling points than alcohols with a
comparable number of carbons.

Similar to alcohols, amines with shorter carbon chains are soluble in
water.
Carbonyl Compounds

A carbonyl group is a functional group with the general structure C=O.

The C=O group is present in aldehydes and ketones.

An aldehyde is an organic compound in which the carbon of the carbonyl group is attached to at least
one hydrogen (general formula RCHO).

A ketone has the carbon of the carbonyl group is joined to two other carbons (general formula RCOR).
Uses of Aldehydes and Ketones

The simplest aldehyde is CH2O, also called formaldehyde. It can be used to preserve biological
structures by combining with protein in tissues to make the tissues hard and insoluble in water.
This prevents the specimen from decaying.

The most common industrial ketone is propanone, also called acetone. It is a colorless liquid that
is used in industry as a solvent. Many nail polish removers contain acetone.
Carboxyl Groups

A carboxyl group is a functional group that consists of a carbonyl group attached to a hydroxyl
group. It can be written as –COOH.

A carboxylic acid is an organic compound with a carboxyl group, general formula RCOOH.

E.g. ethanoic acid a.k.a. acetic acid:
Esters

Esters are probably the most pleasant and delicious organic compounds one can study. They
give blueberries, pineapples, apples, pears, bananas, and many other fruits their characteristic
aromas. They also give many perfumes their fragrances.

An ester is an organic compound in which the –OH of the carboxyl group has been replaced by
an –OR (there is another carbon chain instead of a hydrogen). The general formula of an ester is
RCOOR.
Stop and Check
1.
What is the general formula of an alcohol?
2.
Write the general formula of an ether.
3.
Describe the structure of the carbonyl groups that are characteristic of aldehydes and
ketones.
4.
What is the general formula of an ester?
Polymers

Some of the most important molecules that exist are giant molecules called polymers. For
example, the materials you know as plastics are polymers.

A polymer is a large molecule formed by the covalent bonding of repeating smaller molecules.
The smaller molecules that combine to form a polymer are called monomers.

The reaction that joins monomers to form polymers is called polymerization. Most polymerization
reactions involve a catalyst.
Polymers

The general formula for a polymer is H(-monomer-)XH, where x refers to the number of monomers
that combine.

Polyethylene, which denotes a polymer with ethyl groups as the monomers, is an important
industrial product. It is used to make plastic bottles, containers, and even toys.

The physical properties of polyethylene can be controlled by shortening or lengthening the
carbon chains. Polyethylene with around x=100 short chains has the consistency of paraffin wax.
Polyethylene with long chains (x=1000) is harder and more rigid.
Review

Chapter 22 Review:
 P.

790 #41-50, 53-55, 59-61, 64-69, 71, 73, 80, 85
Chapter 23 Review:
 P.
830 #32-39, 44, 46-47, 49-50, 52, 53 (only name the alcohol)