Chapter 10 Introduction to Organic Chemistry: Alkanes

Chapter 10 Introduction to Organic Chemistry: Alkanes 1

Chemistry for Health Sciences Prof. Ralph Duarte Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition

Copyright © 2012 by Pearson Education, Inc.

Organic Chemistry and Organic Compounds 2

An organic compound • is a compound made from carbon atoms • has one or more C atoms • has many H atoms

• may also contain O, S, N, and halogens • usually has carbon written first

Typical organic compounds • have covalent bonds

• have low melting points • have low boiling points • are flammable

• most are not soluble in water Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition


Organic vs. Inorganic Compounds 3

• Propane, C3H8, is an organic compound used as a fuel. • NaCl, salt, is an inorganic compound composed of Na+ and Cl ions.

Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition


Comparing Organic and Inorganic Compounds 4

Why is propane C3H8 organic, but NaCl is not?



Learning Check 5

Identify each characteristic as most typical of compounds that are inorganic or organic. A. Has a high melting point B. Is not soluble in water C. Has the formula CH3CH2CH3 D. Has the formula MgCl2

E. Burns easily in air F. Has covalent bonds



Solution 6

Identify each characteristic as most typical of compounds that are inorganic or organic. A. Has a high melting point

inorganic

B. Is not soluble in water

organic

C. Has the formula CH3CH2CH3

organic

D. Has the formula MgCl2

inorganic

E. Burns easily in air

organic

F. Has covalent bonds

organic



Bonding in Organic Compounds 7

Bonding in organic compounds: • carbon has 4 valence electrons and hydrogen has only 1 H

C

H C H H

+ 4H

• carbon achieves an octet by forming four bonds, with each line representing 2 electrons H

H H C H H

H

C

H

CH4 methane

H Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition


Tetrahedral Structure of Carbon CH4 8

Carbon atom with four single, covalent bonds has a tetrahedral shape. Methane is represented using different models: (a) tetrahedron (b) ball-and-stick model (c) space-filling model (d) expanded structural formula



Tetrahedral Structure of Carbon C2H6 9

In ethane, • each carbon forms covalent bonds to another carbon and three hydrogen atoms • each carbon atom retains its tetrahedral shape

H H H C C H H H

H

H

H

C

C

H

H

H

Ethane, CH3─CH3 Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition


Tetrahedral Structure of Carbon C2H6 10

In molecules with two or more carbon atoms, each carbon atom with four single bonds has a tetrahedral shape.

Representations of ethane: (a) tetrahedral shape (each carbon) (b) ball-and-stick model (c) space-filling model (d) expanded structural formula



Organic Compounds formed by Hydrogen and Carbon:

Hydrocarbon Compounds. Alkanes 11

Alkanes are organic molecules • containing primarily C–C single bonds • commonly used as fuels for heaters and cooktops • whose names end in ane • named by using the number of carbon atoms connected in a continuous chain



Expanded, Condensed, and Skeletal Structures 12

General Formula of Hexane:

C6H14 An organic molecule can be represented in several ways: • a molecular formula • a ball-and-stick model • an expanded structural formula • a condensed structural formula • a skeletal formula



Condensed Structural Formulas 13

In a condensed structural formula, •

each carbon atom and its attached hydrogen atoms are written as a group

•

a subscript indicates the number of hydrogen atoms bonded to each carbon atom

•

carbon atoms are represented in a straight line

CH3CH2CH2CH3

Example: Expanded view

Expanded view H

H H

C H

butane

=

CH3 Condensed view


C H

=

CH2 Condensed view


Isomers

• Isomers are compounds that have the same molecular formula with different structural arrangements

14

C4H10

CH3CH2CH2CH3 • •

Since atoms can be bonded in different orders, the general molecular formula often applies to different compounds (Example C4H10 isomers). Therefore organic compounds are studied by using their structural formula instead of their general molecular formula.

C4H10

C4H10

CH3  CH3CHCH3


C4H10


The Skeletal Formula 15

 Due to the tetrahedral shape of each carbon atom, the carbon chain shows a zigzag pattern. Example: CH3CH2CH2CH3

Butane can be written as:

• Carbon chains can be written in several chain conformations:



Butane can be written as:


The Skeletal Formula 16

The Skeletal Structural Formula is widely used when representing cyclic structures and more complex molecular structures. Example: Cholesterol Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition


IUPAC Naming of the First Ten Alkanes (using their condensed structural formula) 17



Learning Check 18

Based on the expanded structural formula:

H

H

H

H

H

H

C

C

C

C

C

H

H

H

H

H

1.

What is the molecular formula?

2.

What is the condensed structural formula?

3.

What is the skeletal structural formula?

4.

What is the name? Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition

H


Solution 19

Based on the expanded structural formula:

H

1.

What is the molecular formula?

2.

What is the condensed structural formula?

3.

What is the skeletal structural formula?

4.

What is the name?

H

H

H

H

H

C

C

C

C

C

H

H

H

H

H


H

C5H12 CH3CH2CH2CH2CH3

Pentane Copyright © 2012 by Pearson Education, Inc.

Learning Check 20

Write the condensed structural formula for A. ethane

Write the condensed and skeletal structural formula for B. heptane



Solution 21

Write the condensed structural formula for A. ethane CH3CH3

Write the condensed and skeletal structural formula for B. heptane CH3CH2CH2CH2CH2CH2CH3



Substituents or Attachments to the Carbon Chain 22

Alkane with no substituent

Alkanes with a substituent Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition


Substituent Groups or Attachments 23

Substituents are atoms or groups of atoms attached to the carbon chain and include alkyl and halo groups: Alkyl groups are • carbon branches attached to carbon chains • named with yl ending • named as methyl, ethyl, propyl and isopropyl Halo substituents are • halogens attached to the carbon chain (F, Cl, Br, I) • named as fluoro, chloro, bromo, or iodo Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition


Substituents and Alkyl Groups 24



Guide to Naming Alkanes with Substituents 25



Write IUPAC Names for Alkanes with Substituents 26

Give the IUPAC name for the following compound: Cl  CH3CHCH  CH2 CH3  CH3

Step 1 Write the alkane name of the longest chain of carbon atoms. The longest chain has five carbons, so it is a pentane


Cl  CH3CHCH  CH2 CH3  CH3


Write IUPAC Names for Alkanes with Substituents 27

Step 2 Number the carbon atoms starting from the end nearer a substituent. Cl  #3 #4 #5 CH3CHCH  CH2 CH3 #1

#2

 CH3

Step 3 Give the location and name of each substituent (in alphabetical order) as a prefix to the name of the main chain:

2-chloro-3-methylpentane Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition


Learning Check 28

Give the IUPAC name for the following compound:

H

H

Br

CH3

H

C

C

C

C

Br

H

H

H

H



Solution 29

Give the IUPAC name for the following compound:

H

H

Br

CH3

H

C

C

C

C

Br

H

H

H

H

Step 1 Write the alkane name of the longest chain of carbon atoms. H Br CH3 H The longest chain has four carbons, butane. H C C C C Br Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition

H

H

H

H


Solution 30

Step 2 Number the carbon atoms starting from the end nearer a substituent. H H

1

C Br

Br

2

C H

CH3

3

C H

H

4

C

See substituents shown in circles

H

H

Step 3 Give the location and name of each substituent (in alphabetical order) as a prefix to the name of the main chain. 1,2-dibromo-3-methylbutane Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition


Drawing Formulas for Alkanes 31

Draw the structure for 1-bromo-3,4-dimethylheptane heptane: 7-carbon chain methyl groups on carbon 3 and 4 bromine on carbon 1



Drawing Formulas for Alkanes 32

Draw the structure for 1-bromo-3,4-dimethylheptane heptane: 7-carbon chain methyl groups on carbon 3 and 4 bromine on carbon 1

Solution

Br CH3   CH2 CH2CH  CHCH2CH2CH3  CH3



Guide to Drawing Formulas for Alkanes 33



Learning Check 34

Draw the condensed structural formula for 3-bromo-1-chlorobutane.



Solution 35

Draw the condensed structural formula for 3-bromo-1-chlorobutane. Step 1 Draw the main chain of carbon atoms. The longest chain in butane has four carbon atoms.

CCCC

Step 2 Number chain and place the substituents on the carbons indicated by the numbers. 1 2

3 4

CCCC 3-bromo: Br goes on carbon 3 1-chloro: Cl goes on carbon 1 Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition

Cl

Br


Solution 36

Draw the condensed structural formula for 3-bromo-1-chlorobutane. Step 3 Add hydrogen to complete four bonds to each carbon.

CCCC   Cl Br

(Caution: Hydrogen atoms are missing !!!!!)

CH2CH2CHCH3   Cl Br 3-bromo-1-chlorobutane Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition


Cycloalkanes 37

Cycloalkanes • are cyclic alkanes • have two less hydrogen atoms than the open chain • are named by using the prefix cyclo before the name of the alkane chain with the same number of carbon atoms propane, C3H8

cyclopropane, C3H6

H2 C

H2 C

H3C

CH3


H2C

CH2


Formulas of Cycloalkanes 38



Learning Check 39

Convert the following skeletal structures to condensed structural formulas. Give the IUPAC name for each compound:

A.

B.



Solution 40

Convert the following skeletal structures to condensed structural formulas. Give the IUPAC name for each compound: A.

octane CH3CH2CH2CH2CH2CH2CH2CH3

B.


cyclopentane


Learning Check 41

Name the following alkanes: A.


B.

C.

CH3CH2CH2CH2CH2CH2CH2CH3

D.



Solution 42

Name the following alkanes: A. B.

C.

D.


butane cyclopropane

CH3CH2CH2CH2CH2CH2CH2CH3

octane

cyclohexane



Naming Cycloalkanes with Substituents 43

Give the IUPAC name for the following cycloalkane. CH2CH3

Step 1 Write the alkane name of the longest chain of carbon atoms. C The longest chain is a C C six-member ring, cyclohexane. C

CH2CH3

C C



Solution 44

Step 2 Number the carbon atoms starting from the end nearer a substituent.

C

C C

5 4

6

3

CH2CH3

1C 2C

C

Step 3 Give the location and name of each substituent (in alphabetical order) as a prefix to the name of the main chain. For cycloalkanes with just one substituent, there is no need to give the location of the substituent: ethylcyclohexane



Learning Check 45

Name each of the following cycloalkanes. CH3 A. H2 C

B.

CH3

Cl

C.



Solution 46

Name each of the following cycloalkanes. CH3 A. methylcyclopropane H2 C

B.

CH3

ethylcyclobutane

Cl

C.

chlorocyclopentane



Example Cycloalkane: When three branches are present Problem: Name this cycloalkane 

Parent chain = 6 (cyclohexane)



Which way to number? 





1 , 1, 2 or 1 , 2 , 2

Branches? 

3 branches: one iodo and two ethyl (use prefix di for the two ethyls)



Alphabetize : 1, 2 – diethyl – 1 –iodo

Name: 

1, 2- diethyl -1- iodocyclohexane



Properties of Alkanes: Physical States 48

 Alkanes with one to four carbons are gases at room temperature and are widely used as heating fuels. Example; methane, ethane, propane, butane Butane has four carbons:

 Alkanes with five to eight carbons are highly volatile liquids at room temperature, making them useful in fuels such as gasoline. Example: pentane, hexane, heptane, octane Octane has eight carbons:  Alkanes with 9−17 carbons are liquids with higher boiling points and are found in motor oils, mineral oil, kerosene, diesel, and jet fuels. Decane has 10 carbons: Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition


Properties of Alkanes: Solubility and Density 49

Alkanes are • nonpolar • insoluble in water • less dense than water • flammable in air

Alkanes are insoluble in water

 The crude oil in oil spills floats on top of the water, forming a thin layer on the surface because it is less dense than water. Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition


Some Uses of Alkanes 50

Alkanes with 18 or more carbon atoms • have high molar masses • are waxy solids at room temperature • are used in waxy coatings of fruits and vegetables

Propane is used as a fuel in barbeques Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition



Alkane Mixtures in Crude Oil An oil refinery turns crude oil into usable fuel, producing natural gas, gasoline, kerosene, lubricant oils, and asphalt.




Alkane Mixtures in Crude Oil



Reactions of Alkanes: Combustion 53

• Alkanes have strong CC bonds • Alkanes react with oxygen gas to make carbon dioxide and water in combustion reactions • Alkanes release energy when CC bonds are broken in combustion reactions CH4(g) +

2O2(g)

CO2(g) + 2H2O(g) + energy Combustion reactions are exothermic



Learning Check 54

Write a balanced equation for the complete combustion of propane.



Solution 55

Unbalanced equation: C3H8 + O2

CO2 + H2O

Balance C:

C3H8 + O2

3CO2 + H2O

Balance H: C3H8 + O2

3CO2 + 4H2O

Balance O: C3H8 + 5O2

3CO2 + 4H2O


(balanced) Copyright © 2012 by Pearson Education, Inc.

Reactions of Alkanes: Halogenation



Halogenation of alkanes and alkyl halides 

A hydrogen atom on the alkane or alkyl halide is replaced by one of the two atoms of the halogen molecule (X2 = F2, Cl2, Br2, or I2).



Heat (Δ) or ultraviolet light (uv) needs to be present to make the reaction happen – if neither is present, the reaction does not occur.



Example of Halogenation of Alkanes



Problem: What is the product of the above reaction? 

Halogenation removes a hydrogen from the alkane and replaces it with a halogen

CH3-CH2Br + HBr Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition


Functional Groups 58

In organic molecules, •

Carbon atoms have with four bonds

•

Most bonds are with H and other C atoms

•

sometimes carbon bonds to O, N, S

•

sometimes carbon bonds 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 chain

•

a way to classify families of organic compounds Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition


Alkenes, Alkynes and Aromatic Compounds 59

Alkenes contain a double bond between adjacent carbon atoms. Alkynes contain a triple bond. Aromatic compounds contain a ring of six carbon atoms called benzene.



Comparing Alkenes, Alkynes, and Aromatic Compounds 60



Learning Check 61

Identify the following compounds as alkane, alkene, alkyne or aromatic compound:

A.

E.

B.

F.

C.

G.

D.

H. Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition


Solution 62

Identify the following compounds as alkane, alkene, alkyne or aromatic compound:

A.

B.

C.

D.

Aromatic

Alkene

Alkyne

Alkane

E.

F.

Alkane

Alkene

G. Alkane

H.


Aromatic


Alcohols, Thiols, and Ethers 63

An alcohol contains the hydroxyl (−OH) functional group. Alcohol

CH3CH2OH

A thiol contains the thiol (−SH) functional group. Thiol

CH3CH2SH

An ether contains an oxygen atom bonded to two carbon atoms (COC) functional group. Ether

CH3OCH3



Aldehydes and Ketones 64

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

Aldehyde

O // CH3CH

In a ketone, the carbon of the carbonyl group (C=O) is attached to two carbon atoms.

Ketone

O // CH3CCH3



Carboxylic Acids and Esters 65

Carboxylic acids contain the carboxyl group, (COOH) which is a carbonyl group attached to a hydroxyl group:

Carboxylic acid

O // CH3COH

An ester contains the carboxyl group between carbon atoms (COO-CH3)

Ester

O // CH3COCH3



Amines 66

Amines  have a functional group that contains a nitrogen atom  are derivatives of ammonia, NH3, in which one, two, or three hydrogen atoms are replaced with carbons Amine

CH3NH2

CH3NHCH3


CH3 / CH3NCH3


Amides 67

Amides • have an amine group instead of an OH group on the carbonyl carbon O C N

O // CH3CNH2 Amide

• are an important biological functional group, the simplest amide being urea O C H2 N

NH2


O // NH2CNH2 Copyright © 2012 by Pearson Education, Inc.

Classification of Organic Compounds 68



Learning Check 69

Classify each of the following as an alcohol, ether, aldehyde, ketone, carboxylic acid, ester, amine, or amide. A. B. C. D. E.



Solution 70

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

Alcohol

B.

Ether

C.

Amine

D.

Carboxylic Acid

E.


Ester
