Introduction to Organic Chemistry: Alkanes

Functional Groups

Elements in Organic Compounds

In organic molecules,carbon atoms bond • with four bonds.• mostly with H and

other C atoms.• sometimes to O, N,

S, • sometimes to

halogens F, Cl, and Br.

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 a hydrogen atom in the

corresponding alkane.• a way to classify families of organic compounds.

Functional Groups

Alkenes and Alkynes

Alkenes contain a double bond between adjacent carbon atoms.

Alkynes contain a triple bond.

Copyright © 2005 by Pearson Education, Inc.Publishing as Benjamin Cummings

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– .

Copyright © 2005 by Pearson Education, Inc.Publishing as Benjamin Cummings

Aldehydes and Ketones

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

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

Copyright © 2005 by Pearson Education, Inc.Publishing as Benjamin Cummings

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.

Copyright © 2005 by Pearson Education, Inc.Publishing as Benjamin Cummings

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.

Copyright © 2005 by Pearson Education, Inc.Publishing as Benjamin Cummings

Functional Groups

Copyright © 2005 by Pearson Education, Inc.Publishing as Benjamin Cummings

Learning Check

Classify each of the following as: alcohol, ether, aldehyde, ketone, carboxylic acid, ester, amine or amide.

1) CH3─CH2─CH2─OH

2) CH3─O─CH2─CH3

3) CH3─CH2─NH2

O O ║ ║

4) CH3─C─OH 5) CH3─C─O─CH3

Solution

1) CH3─CH2─CH2─OHalcohol

2) CH3─O─CH2─CH3 ether

3) CH3─CH2─NH2 amine

O O ║ ║ 4) CH3─C─OH 5) CH3─C─O─CH3 carboxylic acid ester

Some functional groups in consumer products

BENGAYCamphor – a ketoneMenthol – an alcoholMethyl salicylate – an ester and a phenol

Neopsporin Miconazole – many functional groups (ether,

chloro)Dimethyl ether propellent

Halls coughMenthol- an alcohol

Some functional groups in spices

Nutmeg Myristicin – a polyether, an aklene, benzene ring Elemicin Safrole

Anise Anethole – an ether, an alkene, benzene ring

Caraway seeds d-Carvone – a ketone

Spearmint l-Carvone – a ketone

Unsaturated Hydrocarbons

Alkenes and Alkynes

Saturated hydrocarbons• have the maximum number of hydrogen atoms

attached to each carbon atom.• are alkanes and cycloalkanes with single C-C

bonds.

CH3—CH2—CH3

Saturated Hydrocarbons

Unsaturated hydrocarbons• have fewer hydrogen

atoms attached to the carbon chain than alkanes.

• are alkenes with double bonds.

• are alkynes with triple bonds.

Unsaturated Hydrocarbons

Bond Angles in Alkenes and Alkynes

According to VSEPR theory: • the three groups bonded to

carbon atoms in a double bond are at 120° angles.

• alkenes are flat because the atoms in a double bond all lie in the same plane.

• the two groups bonded to each carbon in a triple bond are at 180° angles.

Naming Alkenes

The names of alkenes • use the corresponding alkane name.• change the ending to –ene.

Alkene IUPAC Common

H2C=CH2 ethene ethylene

H2C=CH─CH3 propene propylene

cyclohexene

Ethene (Ethylene)

Ethene or ethylene• is an alkene with the formula

C2H4.• has two carbon atoms connected

by a double bond. • has two H atoms bonded to each

C atom.• is flat with all the C and H atoms

in the same plane.• is used to accelerate the ripening

of fruits.

Naming Alkynes

The names of alkynes • use the corresponding alkane name.• change the ending to –yne.

Alkyne IUPAC Common

HC≡CH ethyne acetylene

HC≡C─CH3 propyne

Naming Alkenes and Alkynes

When the carbon chain of an alkene or alkyne has four or more C atoms, number the chain to give the lowest number to the first carbon in the double or triple bond.

CH2=CH─CH2─CH3 1-butene

1 2 3 4

CH3─CH=CH─CH3 2-butene

1 2 3 4

CH3─CH2─CC─CH3 2-pentyne

5 4 3 2 1

Learning Check

Write the IUPAC name for each of the following:

1. CH2=CH─CH2─CH3

2. CH3─CH=CH─CH3

CH3

|3. CH3─CH=C─CH3

4. CH3─CC─CH3

Solution

Write the IUPAC name for each of the following:

1. CH2=CH─CH2─CH3 1-butene

2. CH3─CH=CH─CH3 2-butene

CH3

|3. CH3─CH=C─CH3 2-methyl-2-butene

4. CH3─CC─CH3 2-butyne

Learning Check

Write the IUPAC name for each of the following:

A. CH3─CH2─C≡C─CH3

CH3

B. CH3─CH2─C=CH─CH3

Solution

Write the IUPAC name for each of the following:

A. CH3─CH2─C≡C─CH3 2-pentyne

CH3

B. CH3─CH2─C=CH─CH3 3-methyl-2-pentene

Chapter 11 Unsaturated Hydrocarbons

11.2 Cis-Trans Isomers

Cis and Trans Isomers

In an alkene the double bond, • is rigid.• holds attached groups in fixed positions. • makes cis/trans isomers possible.

CH3 CH3 CH3

CH = CH CH = CH

cis trans CH3

In cis-trans isomers• there is no rotation around

the double bond in alkenes.• groups attached to the

double bond are fixed relative to each other.

You can make a “double bond” with your fingers with both thumbs on the same side or opposite from each other.

Cis-Trans Isomers

Two isomers are possible whengroups are attached to thedouble bond are different.• In a cis isomer, groups are

attached on the same side of the double bond.

• In the trans isomer, the groups are attached on opposite sides.

Cis-Trans Isomers

Cis-Trans Isomerism

• Alkenes cannot have cis-trans isomers if a carbon atom in the double bond is attached to identical groups.

Identical Identical

2-bromopropene 1,1-dibromoethene (not cis or trans) (not cis or trans)

C C

H Br

H CH3

C C

H Br

BrH

H

H

H Br

Cis-Trans Isomers in Nature

• Insects emit tiny quantities of pheromones, which are chemicals that send messages.

• The silkworm moth attracts other moths by emitting bombykol, which has one cis and one trans double bond.

Naming Cis-Trans Isomers

The prefixes cis or trans are placed in front of the alkene name when there are cis-trans isomers. cis

cis-1,2-dibromoethene trans-1,2-dibromoethene

C C

Br H

BrH

C C

Br Br

H H

33

Learning Check

Name each, using cis-trans prefixes when needed.

C C

CH3 H

CH3H

C C

Br Br

H H

A.

B.

C C

CH3 Cl

ClH

C.

34

Solution

cis-1,2-dibromoethene

trans-2-butene

1,1-dichloropropene

C C

CH3 H

CH3H

C C

Br Br

H H

A.

B.

C C

CH3 Cl

ClH

C.

35

Unsaturated Hydrocarbons

Addition Reactions

Addition Reactions

In alkene and alkynes• The double or triple

bond is easily broken, which makes double and triple bonds very reactive.

In addition reactions, reactants are added to the carbon atoms in the double or triple bond.

In hydrogenation, • Hydrogen atoms add to the carbon atoms of a double

bond or triple bond.• A catalyst such as Pt or Ni is used to speed up the

reaction.

Hydrogenation

HC CH + 2H2Ni

HC CH

H H

H H

H2C CH2

H HPt

H2H2C CH2 +

Adding H2 to doublebonds in vegetableoils produces

• Compounds with higher melting points.

• Solids at room temperature such as margarine,

soft margarine, and shortening.

Hydrogenation of Oils

Learning Check

Write an equation for the hydrogenation of 1-butene using a platinum catalyst.

Solution

Write an equation for the hydrogenation of 1-butene using

a platinum catalyst. Pt

CH2=CH─CH2─CH3 + H2 CH3─CH2─CH2─CH3

Trans Fats

In vegetable oils, the unsaturated fats usually containcis double bonds.

• During hydrogenation, some cis double bonds are converted to trans double bonds (more stable) causing a change in the fatty acid structure.

• If a label states “partially” or “fully hydrogenated”, the fats contain trans fatty acids.

Learning Check

(1) True or (2) False

A. ____ There are more unsaturated fats in vegetable oils.

B. ____ Hydrogenation converts some cis-double bonds to

trans- double bonds.

C. ____ Animal fats have more unsaturated fats.

Solution

(1) True or (2) False

A. 1 There are more unsaturated fats in vegetable oils.

B. 1 Hydrogenation of oils converts some cis-double

bonds to trans- double bonds.

C. 2 Animal fats have more unsaturated fats.

Learning Check

Write the product of each the following.

Pt

CH3─CH=CH─CH3 + H2

Pt

+ H2

Solution

Pt

1. CH3─CH=CH─CH3 + H2 CH3─CH2─CH2─CH3

2. + H2 Pt

Hydration

In the addition reaction called hydration,• an acid H+ catalyst is required.• water (HOH) adds to a double bond.• an H atom bonds to one C in the double bond.• an OH bonds to the other C.

H OH

H+ │ │CH3─CH=CH─CH3 + H─OH CH3─CH─CH─CH3

Hydration

When hydration occurs with a double bond that has anunequal number of H atoms,• the H atom bonds to the C in the double bond with the

more H.• the OH bonds to the C in the double bond with the

fewer H atoms.

OH H H+ │ │CH3─CH=CH2 + H─OH CH3─CH─CH2

Learning Check

Write the product for the hydration of each of the

following:

H+

1. CH3─CH2─CH=CH─CH2─CH3 + HOH

CH3

│ H+

2. CH3─C=CH─CH2─CH3 + HOH

H+

3. + HOH

Solution

H OH │ │1. CH3─CH2─CH─CH─CH2─CH3

CH3

│ 2. CH3─C─CH─CH2─CH3

│ │ OH H

OH3. H