Saturated Hydrocarbons Section 20.1 Steven S. Zumdahl Susan A. Zumdahl Donald J. DeCoste Gretchen M. Adams University of Illinois at Urbana-Champaign Chapter.

Saturated Hydrocarbons

Section 20.1

Steven S. Zumdahl

Susan A. Zumdahl

Donald J. DeCoste

Gretchen M. Adams • University of Illinois at Urbana-Champaign

Chapter 20

Organic Chemistry


Section 20.1

1. To understand the types of bonds formed by the carbon atom

2. To learn about the alkanes

3. To learn about structural isomers

4. To learn to draw structural formulas

5. To learn to name alkanes and substituted alkanes

6. To learn about the composition and uses of petroleum

7. To learn about the chemical reactions of alkanes

Objectives


Section 20.1

Carbon Chemistry

• Carbon is unusual. Bonds strongly to itself Forms long chains or rings

• Biomolecule – molecule that functions in maintaining and reproducing life

• Organic compounds – vast majority of carbon compounds Exceptions – oxides and carbonates


Section 20.1

A. Carbon Bonding

• When carbon has 4 atoms bound to it, these atoms have a tetrahedral shape.


Section 20.1

A. Carbon Bonding

Double bond

Triple bond • Sharing of 3 pairs of electrons

• Sharing of 2 pairs of electrons


Section 20.1

B. Alkanes

• Hydrocarbons – compounds composed of carbon and hydrogen Saturated – all carbon-carbon bonds are single bonds Unsaturated – containing carbon-carbon multiple bonds


Section 20.1

B. Alkanes

• Alkanes – saturated hydrocarbons


Section 20.1

B. Alkanes

• Normal, straight-chain or unbranched hydrocarbons

• Contain strings or chains of carbon atoms Representations


Section 20.1

B. Alkanes


Section 20.1

C. Structural Formulas and Isomerism

• Structural isomerism – occurs when 2 molecules have the same atoms but different bonds


Section 20.1

D. Naming Alkanes

• The name for an alkane is based on Greek root with the suffix –ane.

Basic principles


Section 20.1

D. Naming Alkanes

• For branched hydrocarbons use the longest continuous chain for the root name.

Basic principles


Section 20.1

D. Naming Alkanes

• Alkanes missing one H atom can have another hydrocarbon attached at the missing H point.

Basic principles


Section 20.1

D. Naming Alkanes

• Specify the names of substituents by numbering the C atoms starting at the end closest to the branching.

Basic principles


Section 20.1

D. Naming Alkanes

Basic principles


Section 20.1

D. Naming Alkanes

• If a substituent occurs more than once, use a prefix to show this.

Basic principles

2,3-dimethylpentane


Section 20.1

D. Naming Alkanes


Section 20.1

Exercise

Name each of the following:

a)

2,2,4,5-tetramethylhexane

b)

3,6-diethyl-3-methyloctane


Section 20.1

E. Petroleum

• Hydrocarbons are an energy resource.


Section 20.1

E. Petroleum

• Petroleum – thick, dark liquid composed mostly of hydrocarbon compounds

• Natural gas – consists mostly of methane, usually associated with petroleum deposits


Section 20.1

F. Reactions of Alkanes

• Combustion – reaction with oxygen

• Substitution – one or more H atoms are replaced with different atoms


Section 20.1

F. Reactions of Alkanes

• Dehydrogenation – one or more H atoms are removed and the product is an unsaturated hydrocarbon

Section 20.2

Unsaturated Hydrocarbons

1. To learn to name hydrocarbons with double and triple bonds

2. To understand addition reactions

3. To learn about the aromatic hydrocarbons

4. To learn to name aromatic compounds

Objectives

Section 20.2


A. Alkenes and Alkynes

• Alkenes – hydrocarbon containing carbon-carbon double bonds General formula CnH2n

• Alkynes – hydrocarbons containing carbon-carbon triple bonds General formula CnH2n – 2

Section 20.2



Section 20.2


Exercise

Name each of the following:

a)

2,3,5-trimethyl-2-hexene

b)

6-ethyl-3-methyl-3-octene

Section 20.2


• Addition reactions – new atoms form single bonds to the carbons formerly involved in a double or triple bond Hydrogenation – use H2 as the reactant to be added

Reactions of Alkenes

Halogenation – addition of halogen atoms

• Polymerization – joining of many small molecules to form a large molecule


Section 20.2


B. Aromatic Hydrocarbons

• Aromatic hydrocarbons – cyclic unsaturated hydrocarbons with strong aromas

Section 20.2


B. Aromatic Hydrocarbons

• Benzene – simplest aromatic hydrocarbon

Section 20.2


C. Naming Aromatic Compounds

• Monosubstituted benzenes –

use the substituent name as

a prefix of benzene

Section 20.2



• Disubstituted benzenes Use numbers to

indicate the position of substituents and the substituent name as a prefix of benzene.

Section 20.2



• Complex aromatic molecules

Section 20.2


Benzene as a side group is called phenyl

• Phenyl (phenyl group): A portion of a molecular structure which is equivalent to benzene minus one hydrogen atom: -C6H5

Chlorobenzene or Phenyl chloride

Section 20.3

Introduction to Functional Groups and Alcohols

1. To learn the common functional groups in organic molecules

2. To learn about simple alcohols and how to name them

3. To learn about how some alcohols are made and used

4. To learn about simple ethers and how to name them

Objectives

Section 20.3


A. Functional Groups • Functional group – additional atom or groups of atoms

(containing elements in addition to H and C) found on a mostly hydrocarbon molecule

Section 20.3


B. Alcohols

• All alcohols contain the –OH group.

Section 20.3


B. Alcohols

Section 20.3


The different kinds of alcohols

• Alcohols fall into different classes depending on where the –OH is positioned on the chain of carbon atoms.

• There are some chemical differences between the various types.

• Primary, Secondary, and Tertiary alcohols will be discussed on the next several slides.

• Common alcohols: – Methanol-wood alcohol– Ethanol-as an antiseptic and in alcoholic beverages– Isopropanol-in rubbing alcohol

Section 20.3


Primary Alcohols

• In a primary (1o) alcohol, the carbon which carries the –OH group is only attached to one alkyl group.

• Examples of primary alcohols:

Ethanol 1-propanol 2-methyl-1-propanol

Section 20.3


Secondary Alcohols

• In a secondary (2o) alcohol, the carbon with the –OH group attached is joined directly to two alkyl groups, which may be the same or different.

• Examples

2-propanol 2-butanol 3-pentanol

Section 20.3


Tertiary Alcohols

• In a tertiary (3o) alcohol, the carbon with the –OH group attached is joined directly to three alkyl groups, which may be the same or different.

• Examples

2-methyl-2-propanol 2-methyl-2-butanol

Section 20.3


C. Properties and Uses of Alcohols

• Methanol starting material for making acetic acid and many

adhesives, fibers and plastics motor fuel

• Ethanol Fermentation product

Fuel additive used to make gasohol

Section 20.3


C. Properties and Uses of Alcohols

• Other alcohols Ethylene glycol (ethane-1,2-diol) – automotive antifreeze Phenol (benzenol) – production of adhesives and

plastics

Section 20.3


C. Ethers

• An ether is a hydrocarbon with an oxygen sandwiched between the carbons.

• They tend to by very good solvents, much like water, and have relatively low reactivity.

Section 20.3


Rules for Naming Ethers (common method)

• There are two predominate methods of naming ethers. The first is the common method and is most useful with simple ethers.

(The second method is preferred; next slide) • For the first method, if the carbon chains one side of the

oxygen are considered alkyl groups you simply name the groups then write ether.

CH3

CH2

O CH3

Ethyl methyl ether

Section 20.3


Rules for Naming Ethers (Preferred method)

• The other method follows the official IUPAC rules: • Determine the longest alkyl chain for the root name. • Treat the oxygen and the remaining carbons as aside

chain. • The prefix includes the alkyl chain with a suffix of oxy for

the oxygen.

CH3

CH2

O CH3

methoxyethane

Section 20.3


Practice Naming Ethers (answers next slide!)

Section 20.3


Answers to Last Slide

(a) Diisopropyl ether

(a) Cyclopentyl propyl ether

(a) 4-Bromo-1-methoxybenzene

(d) 1-Methoxycyclohexene

(d) Ethyl isobutyl ether

Section 20.3


Preparation of Ethers

• Dehydration of two alcohols:

• Alkyl halide and alkoxide:

Section 20.4

Additional Organic Compounds

1. To learn about aldehydes and ketones

2. To learn to name aldehydes and ketones

3. To learn about some common carboxylic acids and esters

4. To learn about amines.

5. To learn how to name amines.

6. To learn about some common polymers

Objectives

Section 20.4


A. Aldehydes and Ketones

• Carbonyl group – carbon oxygen group found in both aldehydes and ketones

Ketone – carbonyl group is bonded to two carbon atoms

Section 20.4



Aldehyde – carbonyl group always appears on the end of the hydrocarbon chain and has at least one H atom bonded to the carbonyl group

Section 20.4



Section 20.4


B. Naming Aldehydes and Ketones

• Aldehydes

Use the parent alkane name. • Remove the e and replace it with al.

Section 20.4


B. Naming Aldehydes and Ketones

• Ketones

Use the parent alkane name. • Remove the e and replace it with one. • Use a number to indicate the position of the

carbonyl group in the hydrocarbon chain. Select the number so that the carbonyl has the lowest

possible number.

Propanone (acetone)2-butanone (methyl-ethyl-ketone MEK)

Section 20.4


C. Carboxylic Acids and Esters

• Carboxylic acids – contains the carboxyl group

COOH

• General formula RCOOH • Weak acids in solution

Section 20.4



• To name carboxylic acids

Use the parent alkane name. • Remove the e and replace it with oic.

Section 20.4



Section 20.4



• Esters – a carboxylic acid reacts with an alcohol to form an ester and a water molecule

General formula

Section 20.4



• To name esters

Use the alkyl name from the alcohol followed by the acid name, where the –ic ending is replaced by –ate.

isopropylethanoate

Section 20.4


Amines

• What are amines?

• The easiest way to think of amines is as near relatives of ammonia, NH3.

• In amines, the hydrogen atoms in the ammonia have been replaced one at a time by hydrocarbon groups.

On this page, we are only looking at cases where the hydrocarbon groups are simple alkyl groups.

Section 20.4


The different kinds of amines

• Amines fall into different classes depending on how many of the hydrogen atoms are replaced.

Primary Secondary Tertiary

In a primary (1°) amine, one carbon group is bonded to the nitrogen atom.

A secondary (2°) amine has two carbon groups.

A tertiary (3°) amine has three carbon groups.

Section 20.4


Common Names of Amines

• Simple amines are named as alkylamines.• The alkyl groups bonded to the N atom are listed in

alphabetical order in front of amine.

Section 20.4


IUPAC Names of Amines

• In the IUPAC system, amines are named as alkanamines.

• The –e in the alkane name of the longest chain is changed to –amine.

• The chain is numbered to locate the amine group and substituents.

Section 20.4


Primary amines

• In primary amines, only one of the hydrogen atoms in the ammonia molecule has been replaced.

That means that the formula of the primary amine will be R-NH2 where "R" is an alkyl group.

• Examples include:

MethanamineEthanamine Propanamine Isopropanamine

Section 20.4


• The common name at this level is methylamine and, similarly, the second compound drawn above is usually called ethylamine.

• Where there might be confusion about where the -NH2 group is attached to a chain, the simplest way of naming the compound is to use the "amino" form.

Section 20.4


Secondary amines

• In a secondary amine, two of the hydrogens in an ammonia molecule have been replaced by hydrocarbon groups. At this level, you are only likely to come across simple ones where both of the hydrocarbon groups are alkyl groups and both are the same.

• Dimethanamine diethanamine

Section 20.4


Tertiary amines

• In a tertiary amine, all of the hydrogens in an ammonia molecule have been replaced by hydrocarbon groups. Again, you are only likely to come across simple ones where all three of the hydrocarbon groups are alkyl groups and all three are the same.

• The naming is similar to secondary amines. For example:

Section 20.4


Physical Properties of Amines

We will look at the boiling point difference on the next several slides.

Section 20.4


Primary amines

• It is useful to compare the boiling point of methylamine, CH3NH2, with that of ethane, CH3CH3.

• Both molecules contain the same number of electrons and have, as near as makes no difference, the same shape. However, the boiling point of methylamine is -6.3°C, whereas ethane's boiling point is much lower at -88.6°C.

• The reason for the higher boiling points of the primary amines is that they can form hydrogen bonds with each other as well as van der Waals dispersion forces and dipole-dipole interactions.

Section 20.4


Secondary amines

• For a fair comparison you would have to compare the boiling point of dimethylamine with that of ethylamine. They are isomers of each other - each contains exactly the same number of the same atoms.

• The boiling point of the secondary amine is a little lower than the corresponding primary amine with the same number of carbon atoms.

• Secondary amines still form hydrogen bonds, but having the nitrogen atom in the middle of the chain rather than at the end makes the permanent dipole on the molecule slightly less.

• The lower boiling point is due to the lower dipole-dipole attractions in the dimethylamine compared with ethylamine.

Section 20.4


Tertiary amines

• This time to make a fair comparison you would have to compare trimethylamine with its isomer 1-aminopropane.

• If you look back at the table on slide 18, you will see that the trimethylamine has a much lower boiling point (3.5°C) than 1-aminopropane (48.6°C).

• In a tertiary amine there aren't any hydrogen atoms attached directly to the nitrogen. That means that hydrogen bonding between tertiary amine molecules is impossible. That's why the boiling point is much lower.

Section 20.4


Solubility in water•The small amines of all types are very soluble in water. In fact, the ones that would normally be found as gases at room temperature are normally sold as solutions in water - in much the same way that ammonia is usually supplied as ammonia solution.

Smell•The very small amines like methylamine and ethylamine smell very similar to ammonia - although if you compared them side by side, the amine smells are slightly more complex.•As the amines get bigger, they tend to smell more "fishy", or they smell of decay.

Section 20.4


D. Polymers

• Polymers – large chainlike molecules made from many small molecules called monomers Simplest polymer – polyethylene Polyethylene results from addition polymerization.

Section 20.4


D. Polymers

• Condensation polymerization – a small molecule (often water) is released for each addition of a monomer to the polymer chain

• Copolymer – 2 different types of monomers combine to form the chain

Nylon (co-polymer)

Section 20.4


Sodium Silicate polymer

• When sodium silicate and ethyl alcohol are put together, the silicate particles begin to link up with each other to form long chains as the ethyl groups (sometimes shown as "R") replace oxygen atoms in the silicate ion. (Some become cross-linked between chains.) Water molecules are by-products of the formation of the polymerization bond.

• The large molecule is a solid. It is a type of silicone polymer.

Saturated Hydrocarbons Section 20.1 Steven S. Zumdahl Susan A. Zumdahl Donald J. DeCoste Gretchen M. Adams University of Illinois at Urbana-Champaign Chapter.

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