1 chapter 11 introduction to organic chemistry: alkanes 11.4 properties of alkanes copyright © 2007...

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Chapter 11 Introduction to Organic Chemistry: Alkanes

11.4

Properties of Alkanes

Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

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Some Properties of Alkanes

The properties of alkanes include

being Nonpolar. Insoluble in water. Less dense than water Flammable in air.


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Alkanes with 1-4 Carbon Atoms

Alkanes with 1-4 carbon atoms are Methane, ethane, propane, and

butane. Gases at room temperature. Used as heating fuels.


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Alkanes with 5-17 Carbon Atoms

Alkanes with 5-8 carbon atoms are Liquids at room temperature. Pentane, hexane, heptane, and octane. Very volatile. Used to make gasoline.

Alkanes with 9-17 carbon atoms Are liquids at room temperature Have higher boiling points. Are found in kerosene, diesel, and jet fuels.

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Alkanes with 18 or more Carbon Atoms

Alkanes with 18 or more carbon atoms Have high molar masses. Are waxy solids at room temperature. Used in waxy coatings of fruits and

vegetables.


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Boiling Points of Alkanes

Are lowest of organic compounds.

Increase with larger molecules due to increased dispersion forces.

Decrease for branched alkanes.

Increase for cycloalkanes.

TABLE 11.6

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Sample Question – Boiling Point

For the following pairs of hydrocarbon, which one has

the higher boiling point? Why?

1. butane or octane

2. hexane or 2,3-dimethylbutane

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Solution

For the following pairs of hydrocarbon, which one has

the higher boiling point? Why?

1. butane or octane octane has more carbon atoms

2. hexane or 2,3-dimethylbutane

hexane is not branched

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Crude Oil

The hydrocarbons incrude oil are Separated by

boiling points. Heated to higher

temperatures to produce gases that can be removed and cooled.


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Classification of Carbon Atoms

The classification of carbon atoms indicates the

number of carbon atoms attached. A primary carbon (1°) bonds to one carbon atom. A secondary carbon (2°) bonds to two carbon atoms. A tertiary carbon (3°) bonds to three carbon atoms.

CH3

|

CH3 —CH2—CH2—CH3 CH3—CH—CH3

primary secondary tertiary

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Combustion of Alkanes

Alkanes

Undergo combustion by reacting with oxygen to produce carbon dioxide, water, and energy.

Are typically not very reactive due to strong C-C single bonds.

alkane + O2 CO2 + H2O + energy


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Balancing a Combustion Reaction

Propane is used to provide heat for

cooking or warming a room. Write a

balanced equation for the complete

combustion of propane.


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Halogenation of Alkanes (Substitution)

When alkanes react with halogens,

The reaction is called substitution, one or more H atoms are replaced with a halogen usually Cl or Br.

Light or heat is required.

A mixture of halogenated products result, but we write the

equation with the monosubstituted product.

Example: ethane and chloride

light

CH3—CH3 + Cl2 CH3—CH2 —Cl

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Example of Bromination

Give the structures and names of the possible monosubstituted products for the reaction of propane with bromine in the presence of light.

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Solution

Give the structures and names of the possible monosubstituted products for the reaction of propane with bromine in the presence of light.

CH3—CH2—CH2— Br

1-bromopropane; propyl bromide

Br

|

CH3—CH—CH3

2-bromopropane; isopropyl bromide

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Functional groups are A characteristic feature of organic molecules that

behave in a predictable way. Composed of an atom or group of atoms. Groups that replace an H in the corresponding

alkane. A way to classify families of organic compounds.

Functional Groups

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Alkenes and Alkynes

Alkenes contain a double bond between adjacent carbon atoms.

Alkynes contain a triple bond.


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Alcohols and Ethers

An alcohol contains the hydroxyl (-OH) functional group.

In an ether, an oxygen atom is bonded to two carbon atoms

–C–O–C– .


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Aldehydes and Ketones

An aldehyde contains a carbonyl group (C=O), which is a carbon atom with a double bond to an oxygen atom, attached to at least one hydrogen.

In a ketone, the carbon of the carbonyl group is attached to two other carbon atoms.


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Carboxylic Acids and Esters

Carboxylic acids contain the carboxyl group, which is a carbonyl group attached to a hydroxyl group. O

— C—OH An ester contains the

carboxyl group between carbon atoms.


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Amines and Amides

In amines, the functional group is a nitrogen atom.

|

—N —

In amides, the hydroxyl group of a carboxylic acid is replaced by a nitrogen group.


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Functional Groups in Everyday Items

Methyl amine (fish)


1 chapter 11 introduction to organic chemistry: alkanes 11.4 properties of alkanes copyright © 2007...

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