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Ch. 10: Alkanes

Chem 20

El Camino College

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Organic Chemistry

More than 90% of compounds are organic compounds.

For pronunciation of organic compound names go to

www.merriam-webster.com/dictionary

www.howjsay.com

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Organic Chemistry

Organic chemistry covers compounds made of carbon and hydrogen

Other elements, such as O, N, S and Cl may be present

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Organic Chemistry

Organic compoundsThey are mostly covalently bonded

moleculesUsually low melting pointsUsually low boiling pointsThey are usually not soluble in water,

unless a polar group is present

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Organic Chemistry

Inorganic compoundsThey are mostly ionic compounds, some are

covalentUsually high melting pointsUsually high boiling pointsThey are usually soluble in water.

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ALKANES

Remember that carbon has 4 bonds and is often tetrahedral.

Wedge formula: Solid wedge represents bond coming forward. Broken wedge represents bond going to the back. Ordinary line represents bond on the plane

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Lewis Structures

Each bonding pair is represented by a dash. Sometimes we draw long molecules with straight lines, but actually they are not flat

C O C H

H

H

H

H

H

::

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Alkanes

Alkanes are a class of hydrocarbons in which the atoms are connected only by single bonds.

The general formula for open-chain alkanes is Cn H2n+2 .

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Alkanes CH4 methane (1C)

CH3CH3 ethane (2C)

CH3CH2CH3 propane (3C)

CH3CH2CH2CH3 butane (4C)

CH3CH2CH2CH2CH3 pentane (5C)

CH3CH2CH2CH2CH2CH3 hexane (6C)

CH3CH2CH2CH2CH2CH2CH3 heptane (7C)

CH3CH2CH2CH2CH2CH2CH2CH3 octane (8C)

CH3CH2CH2CH2CH2CH2CH2CH2CH3 nonane (9C)

CH3CH2CH2CH2CH2CH2CH2CH2CH2CH3 decane (10C)

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Drawing Formulas

In expanded formulas, every bond is shown In condensed formulas, carbons are shown with

the correct number of hydrogen atoms, but not every bond is shown

In alkane, C will always have 4 bonds, H will always have 1 bond

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Drawing Formulas

C

H

H

H

H3C

C

H

H

CH2

C C

H

H

H

H

H

H3C CH2

H3CH2C

or

expanded

condensed

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Drawing Formulas Hexane has six carbons. Draw expanded

and condensed formulas for hexane. (Note: make sure every carbon has 4 bonds)

C C

H

H

H

H

C

H

C C C H

H

H

H

H

H

H

H

H

H3C CH2 CH2 CH2 CH2 CH3

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Drawing Formulas Note--the chains in formulas may not be

shown as a straight line. Ex. What compounds are these?

H3C CH2 CH2

H2C CH2

CH2H3C

H3C CH2

CH2H3C

butane heptane

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Skeletal (Geometric)Formula(Stick structure)

Skeletal formulas contain zigzag lines Every corner and every end represents a carbon H atoms are filled in mentally Butane:

Hexane

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Structural Isomers Isomers have the same chemical formula, but

atoms are attached differently 2 different isomers have different properties Are these isomers, or the same molecule?

or

or

isomers

same molecule

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Stereoisomers In stereoismers atoms are attached to each other in the same

way But they are different in the way atoms are oriented in space Chiral center is a carbon atom to which 4 different groups are

attached.

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Fisher projection A cross represents a chiral center. Vertical lines represent bonds going away to the back Horizontal lines represent bond coming forward

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Cycloalkanes Cycloalkanes have the carbons connected in a “ring” Use cyclo in the name Ex. Condensed formula

for cyclohexane

Draw a geometric formula for cyclopropane.What is the chemical formula?

H2C

H2C

CH2

CH2

CH2

CH2

C3H6

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Substituents Alkanes can have attachments Common attachment names:

• CH3- methyl

• CH3CH2- ethyl

• CH3CH2CH2- propyl

• F-, Cl-, Br-, I-fluoro, chloro, bromo, iodo

• isopropyl

HC

H3C

H3C

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Alkanes with Substituents 1. Write the name of the longest continuous

carbon chain H3C CH2 CH2

HC CH3

CH3

The longest chain has 5 carbons: pentane

H3C CH2 CH2

HC CH3

CH3

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Alkanes with Substituents 2. Number the carbon chain from the end

nearer a substituent

3. Give the location and name of the substituent. Use a hyphen after the number

H3C CH2 CH2

HC CH3

CH31

2

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2-methylpentane

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Alkanes with Substituents

Name these

2-chloropentane 3-chloropentane

Cl

Cl

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Alkanes with Substituents

Name these

C C

H

H

H

H

C

H

C C C H

H

H

H

H

CH2

H

H

H

H3C

Br

2-bromopropane 3-methylheptane

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Alkanes with Substituents Name these, write the formula

1-bromohexaneC6H13Br

4-ethylnonaneC11H24

Br

3-methylnonaneC10H22

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Alkanes with Substituents Draw the skeletal formula

Draw the expanded formula

Br

2-bromobutane

1-iodopropane

1-chlorodecane

cyclobutane

Cl

H C C C H

I

H H

H H

H

C

C C

C

H

H

H

H

H

H

H

H

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Alkanes with Substituents Name these, write the formula

cyclopentaneC5H10

2-fluorohexaneC6H13F

4-propylheptaneC10H22

F

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Alkanes with Substituents 4. Name substituents in alphabetical order

Name this2-bromo-1-iodohexane

C C

H

H

H

H

C

H

C C C H

H

H

H

H

H

Br

H

I

CH3

Br 3-bromo-2-methylpentane

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Alkanes with Substituents Name these

1-bromo-2-chlorobutane

2-chloro-1-fluorobutane

Cl

Br

Cl

F

F

Br

1-bromo-1-fluoro-2-methylpropane

5. Use prefixes like di-, tri-, tetra- for more than one copy of a substituent Every substituent must have its own number Prefixes are not part of alphabetical order.

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2,3-dimethylbutane

2,2-dibromobutane

C C

H

H

H

CH3

C

H

C

H

CH3

H

H

H

Br Br Cl Cl

Cl

1,2,2-trichlorobutane

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C C

H

Br

H

Br

C

H

C

H

CH3

H

H

H

C C

H

Br

H

Br

CH

H H

CH3

F

Br

3-bromo-2-fluoropentane

1,2-dibromo-3-methylbutane

1,2-dibromobutane

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7. When a single substituent is attached to a cycloalkane, no number is needed.

ethylcyclobutane

Cl

chlorocyclohexane

Write the name and chemical formula:

C6H12

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Draw these ethane 2-methylpropane

bromocyclopentane

1,4-dichloro-2-methylbutane

1,1,2,3-tetrabromopropane

Br

Cl

ClCH3

Br

Br

Br

Br

H3C CH3

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Properties, Uses Alkanes are nonpolar, so they’re insoluble in water Alkanes are less dense than water (they float on

water) Common alkanes: methane (natural gas), propane

(bbq fuel), butane (lighter fuel), octane (fuel) Alkane mixtures also form gasoline, mineral oil,

and vaseline.

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Combustion The burning of methane in a Bunsen burner is

an example of combustion of an alkane alkane + O2 CO2 + H2O + energy Write a balanced equation for the combustion

of methane gas

_____(g) + O2(g) CO2(g) + H2O(g)CH4 22

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Compound TypesAlkenes (contain C=C)Alkynes (contain CC)Alcohols (contain -OH)Ethers (contain C-O-C)Aldehydes (contain H-C=O)Ketones (contain C=O)Carboxylic acids (contain HO-C=O)Esters (contain RO-C=O)Amines (contain N).

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What is the compoud type?

H3C

C

CH3

O

H3C OCH3

O

H3C

C

OH

O

H3C

C

H

O

alkene

ketone

amine

ester

carboxylic acid

aldehyde

alkaneH3C

NH

CH3

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Substitution Reactions Your next organic reactions will be on

haloalkanes (alkanes with a halogen atom substituent)

In substitution reactions, one halogen will be substituted for another halogen

CH3Br + Cl- CH3Cl + Br-

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Draw Products, Name the Organic Product

chloroethane

H3C CH2Br + Cl - H3C CH2Cl + Br -

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Draw Products, Name the Organic Product

2-chloro-2-methylpropane

CH3

C I

CH3

H3C + Cl- + I -

CH3

C Cl

CH3

H3C

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Name These

bromoethane

Br Br

Br

Br BrBr BrBr

Br

bromoethane

1,1-dibromoethane

1,2-dibromoethane

1,1,2-tribromoethane

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Name These

2-bromopropane

2-bromo-2-methylpropane

1,2-dibromo-2-methylpropane

1,1,1,2-tetrabromo-2-methylpropane

Br

Br Br

Br Br Br

Br

Br

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Draw Products, Name the Organic Product

+ Br-

Cl

bromocyclohexane

+ Cl-

Br