3 ch241 alkanes (2)

3. Organic Compounds: Alkanes and 3. Organic Compounds: Alkanes and Their StereochemistryTheir Stereochemistry

Why this ChapterWhy this ChapterAlkanes are unreactive, but provide useful vehicle to introduce important ideas about organic compounds

Alkanes will be used to discuss basic approaches to naming organic compounds

We will take an initial look at 3-D aspects of molecules

2

3.1 Functional Groups3.1 Functional Groups Functional group -

collection of atoms at a site that have a characteristic behavior in all molecules where it occurs

The group reacts in a typical way, generally independent of the rest of the molecule

For example, the double bonds in simple and complex alkenes react with bromine in the same way

Functional Groups with: Functional Groups with: Multiple Carbon–Carbon BondsMultiple Carbon–Carbon Bonds

Alkenes have a C-C double bondAlkynes have a C-C triple bond

Arenes have special bonds that are represented as alternating single and double C-C bonds in a six-membered ring

4

Alkenes and AlkynesAlkenes and Alkynes

Alkenes contain a double bond between adjacent carbon atoms.

Alkynes contain a triple bond.

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

Functional Groups with: Functional Groups with: Carbon Singly Bonded to an Electronegative AtomCarbon Singly Bonded to an Electronegative Atom

Alcohols and EthersAlcohols and EthersAn alcohol contains

the hydroxyl (-OH) functional group.

In an ether, an oxygen atom is bonded to two carbon atoms –C–O–C– .


Functional Groups with: Functional Groups with: Carbon–Oxygen Double Bond (Carbonyl Groups)Carbon–Oxygen Double Bond (Carbonyl Groups)

8

Aldehydes and KetonesAldehydes and KetonesAn 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.


9

Carboxylic Acids and EstersCarboxylic Acids and Esters

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

— C—OHAn ester contains the carboxyl

group between carbon atoms.


10

Amines and AmidesAmines 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.


11

Summary of Functional GroupsSummary of Functional Groups

12

Survey of Functional GroupsSurvey of Functional Groups

13

Survey of Functional GroupsSurvey of Functional Groups

14

Methyl amine (fish)


Functional Groups in Everyday Functional Groups in Everyday ItemsItems

15

Learning CheckClassify each of the following as alcohol, ether, aldehyde, ketone, carboxylic acid, ester, or amine.

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

16

SolutionClassify each of the following as alcohol, ether, aldehyde, ketone, carboxylic acid, ester, or amine.1) CH3─CH2─CH2─OH 2) CH3─O─CH2─CH3

alcohol ether

3) CH3─CH2─NH2 amine O O || ||

4) CH3─C─OH 5) CH3─C─O─CH3

carboxylic acid ester

What functional group is not present in the naturally What functional group is not present in the naturally occurring compound shown below? occurring compound shown below?

1. carboxylic acid2. amine3. primary alcohol4. secondary alcohol5. methyl group

H3C OH

OOH

NH2

Learning Check

What functional group is not present in the naturally What functional group is not present in the naturally occurring compound shown below? occurring compound shown below?

1. carboxylic acid2. amine3. primary alcohol4. secondary alcohol5. methyl group

H3C OH

OOH

NH2

Solution

19

3.2 Alkanes and Alkane Isomers3.2 Alkanes and Alkane IsomersAlkanes: Compounds with C-C single bonds and C-H bonds

only (no functional groups)Connecting carbons can lead to large or small moleculesThe formula for an alkane with no rings in it must be

CCnnHH2n+22n+2 where the number of C’s is nAlkanes are saturatedsaturated with hydrogen (no more can be

addedThey are also called aliphatic compounds

21

Condensed Structures of AlkanesCondensed Structures of AlkanesWe can represent an alkane in a brief form or in many

types of extended formA condensed structure does not show bonds but lists

atoms, such as ◦ CH3CH2CH2CH3 (butane)

◦ CH3(CH2)2CH3 (butane)

22

Expanded and Condensed StructuresExpanded and Condensed Structures

23

Some Structures for ButaneSome Structures for Butane


24

Line-Bond FormulasLine-Bond FormulasBecause each C atom has a tetrahedral

arrangement, the order of atoms is not a straight line, but a zigzag pattern.

A line-bond formula abbreviates the carbon atoms and shows only the zigzag pattern of bonds from carbon atom to carbon atom.

25

Hexane has Six Carbon AtomsHexane has Six Carbon Atoms

Hexane Is an alkane with 6 carbon atoms in a

continuous chain.Has a “zig-zag” look because each carbon

atom is at the center of a tetrahedron.Is represented by a ball-and-stick model

as

26

Learning Check Learning Check A. Write the condensed formula for:

H H H H H

H C C C C C H

H H H H H

B. What is its molecular formula?

C. What is its name?

27

SolutionSolutionA. Write the condensed formula for:

H H H H H

H C C C C C H

H H H H H

B. What is its molecular formula?

C. What is its name?

CH3CH2CH2CH2CH3

C5H12

pentane

28

Learning CheckLearning CheckWrite the condensed structural formula for

A. ethane

B. heptane

29

SolutionSolutionWrite the condensed structural formula for

A. ethane CH3 CH─ 3

B. heptane CH3 CH─ 2 CH─ 2 CH─ 2 CH─ 2 CH─ 2 CH─ 3

30

Alkane IsomersAlkane IsomersCH4 = methane, C2H6 = ethane, C3H8= propane

The molecular formula of an alkane with more than three carbons can give more than one structure◦ C4 (butane) = butane and isobutane

◦ C5 (pentane) = pentane, 2-methylbutane, and 2,2-dimethylpropane

Alkanes with C’s connected to no more than 2 other C’s are straight-chain or normal alkanes

Alkanes with one or more C’s connected to 3 or 4 C’s are branched-chain alkanes

31

Constitutional IsomersConstitutional Isomers Isomers that differ in how their atoms are arranged in

chains are called constitutional isomersCompounds other than alkanes can be constitutional

isomers of one anotherThey must have the same molecular formula to be isomers

32

Isomers of ButaneIsomers of ButaneIsomersHave the same

molecular formula.

Have different atom arrangements.

Of butane (C4H10) consist of a straight chain and a branched chain each with 4 carbon atoms.

branch

What kind of carbon What kind of carbon is notis not present in the molecule present in the molecule below?below?

1. primary2. secondary3. tertiary4. quaternary5. All 4 kinds of carbon

are present

HO

Learning Check

What kind of carbon What kind of carbon is notis not present in the molecule present in the molecule below?below?

1. primary2. secondary3. tertiary4. quaternary5. All 4 kinds of carbon

are present

HO

Solution

How many secondary hydrogens are there in the How many secondary hydrogens are there in the following molecule?following molecule?

1. 22. 33. 44. 55. 6

Learning Check

How many secondary hydrogens are there in the How many secondary hydrogens are there in the following molecule?following molecule?

1. 22. 33. 44. 55. 6

Solution

Which of the following choices Which of the following choices is notis not an an alkane?alkane?

1. C12H26

2. C10H20

3. C11H24

4. C16H34

5. C20H42

Learning Check

Which of the following choices Which of the following choices is notis not an an alkane?alkane?

1. C12H26

2. C10H20

3. C11H24

4. C16H34

5. C20H42

Solution

A brilliant chemist determined the number of A brilliant chemist determined the number of secondary secondary carbons and carbons and secondarysecondary hydrogens for an unknown alkane. hydrogens for an unknown alkane. Well, actually, the chemist is having trouble deciding which Well, actually, the chemist is having trouble deciding which numbers are correct. Which of these answers is possible for numbers are correct. Which of these answers is possible for an alkane?an alkane?

2° hydrogens 2° carbons

1. 6 22. 4 43. 3 54. 3 65. 8 4

Learning Check

A brilliant chemist determined the number of A brilliant chemist determined the number of secondary secondary carbons and carbons and secondarysecondary hydrogens for an unknown alkane. hydrogens for an unknown alkane. Well, actually, the chemist is having trouble deciding which Well, actually, the chemist is having trouble deciding which numbers are correct. Which of these answers is possible for numbers are correct. Which of these answers is possible for an alkane?an alkane?

2° hydrogens 2° carbons

1. 6 22. 4 43. 3 54. 3 65. 8 4

Solution

42

3.4 Naming Alkanes3.4 Naming AlkanesCompounds are given systematic names by a process that

uses

Follows specific rules◦ Find parent hydrocarbon chain◦ Carbons in that main chain are numbered in sequence◦ Substituents are identified numbered◦ Write compound name is single word ◦ Name a complex substituents as though it were a

compound itselfSee specific examples in text

43

IUPAC Names for Simple AlkanesIUPAC Names for Simple Alkanes•Use a prefix to indicate the number of carbons in a chain.•End in –ane.

44

Learning CheckLearning CheckA. Give the name of each compound:

1) CH3—CH3

2) CH3—CH2—CH3

3) CH3—CH2—CH2—CH2—CH2—CH3

B. Write the condensed structural formula of pentane.

45

SolutionSolutionA. Give the name of each compound:

1) CH3—CH3 ethane

2) CH3—CH2—CH3 propane

3) CH3—CH2—CH2—CH2—CH2—CH3

hexaneB. Write the condensed structural formula of

pentane.CH3—CH2—CH2—CH2—CH3

46

3.3 Alkyl Groups3.3 Alkyl GroupsAlkyl group – remove one H from an alkane (a part of a

structure)

General abbreviation “R” (for Radical, an incomplete species or the “rest” of the molecule)

Name: replace -ane ending of alkane with -yl ending◦ CH3 is “methyl” (from methane)

◦ CH2CH3 is “ethyl” from ethane

48

Types of Alkyl groupsTypes of Alkyl groups

Classified by the connection site (See Figure 3.3)◦ a carbon at the end of a chain (primary alkyl group)◦ a carbon in the middle of a chain (secondary alkyl group)◦ a carbon with three carbons attached to it (tertiary alkyl

group)

49

Naming SubstituentsNaming SubstituentsCH3

CH2 CH3

CH2 CH2 CH3

CHCH3

CH3

CH2 CH

CH3

CH3

CH2 CH2 CH2 CH3

CH

CH3

CH2 CH3

C

CH3

CH3

CH3

IUPAC Common

methyl methyl

ethyl ethyl

propyl n-propyl

1-methylethyl Isopropyl

butyl n-butyl

1-methylpropyl sec-butyl

2-methylpropyl Isobutyl

1,1-dimethylethyl tert-butyl ort-butyl

IUPAC Common

pentyl n-pentyl oramyl

1-methylbutyl sec-pentyl

3-methylbutylisopentyl orisoamyl or i-amyl

1,1-dimethylpropyl

tert-pentyl ortert-amyl or t-amyl

2,2-dimethylpropyl

neopentyl

50

Naming SubstituentsNaming Substituents

CH2 CH2 CH CH3

CH3

CH2 CH2 CH2 CH2

CH

CH3

CH2 CH2

C

CH3

CH2

CH3

CH3

CH3

CH3

CH2 C

CH3

CH3

CH3

51

Naming SubstituentsNaming SubstituentsIUPAC

Fluoro

Chloro

Bromo

Iodo

Hydroxy

F

Cl

Br

I

OH

52

Alkanes with Alkyl GroupsAlkanes with Alkyl Groups

CH3 CH CH3

CH3 methylpropane

2,4-dimethylpentane

methyl groupsmethyl groups

CH3 CH

CH3

CH2 CH

CH3

CH3

53

Write three isomers of C5H12 and name each.

Learning CheckLearning Check

54

Write three isomers of C5H12 and name each.

SolutionSolution

A chain of 5 carbon atoms CH3 CH─ 2 CH─ 2 CH─ 2 CH─ 3

pentane

A chain of 4 carbon atoms and 1 carbon branch CH3

│CH3 CH CH─ ─ 2 CH─ 3 2-methylbutane

A chain of 3 carbon atoms and 2 carbon branches CH3

│CH3 C CH─ ─ 3 2,2-dimethylpropane │ CH3

What is the best IUPAC name for the following What is the best IUPAC name for the following compound?compound?

1. 2-ethyl-3-isopropylhexane2. 1-isopropyl-3-ethylhexane3. 4-isopropyl-5-ethylhexane4. 3-methyl-4-isopropylheptane5. 4-isopropyl-3-methylheptane


What is the best IUPAC name for the following What is the best IUPAC name for the following compound?compound?

1. 2-ethyl-3-isopropylhexane2. 1-isopropyl-3-ethylhexane3. 4-isopropyl-5-ethylhexane4. 3-methyl-4-isopropylheptane5. 4-isopropyl-3-methylheptane

SolutionSolution

What is the systematic name of the alkane shown What is the systematic name of the alkane shown below?below?

1. 3,7-dimethyl-4-propyloctane2. 2-methyl-5-(1-methylpropyl)octane3. 2-ethyl-6-methyl-3-propylheptane4. 3-methyl-4-(3-methylbutyl)heptane5. 2,6-dimethyl-5-propyloctane


What is the systematic name of the alkane shown What is the systematic name of the alkane shown below?below?

1. 3,7-dimethyl-4-propyloctane2. 2-methyl-5-(1-methylpropyl)octane3. 2-ethyl-6-methyl-3-propylheptane4. 3-methyl-4-(3-methylbutyl)heptane5. 2,6-dimethyl-5-propyloctane

SolutionSolution

Which of the following Which of the following is notis not an isomer of an isomer of hexane?hexane?

1. 2,2-dimethylbutane2. 2,2-dimethylpentane3. 3-methylpentane4. 2-methylpentane5. 2,3-dimethylbutane


Which of the following Which of the following is notis not an isomer of an isomer of hexane?hexane?

1. 2,2-dimethylbutane2. 2,2-dimethylpentane3. 3-methylpentane4. 2-methylpentane5. 2,3-dimethylbutane

SolutionSolution

How many constitutional isomers of How many constitutional isomers of CC44HH1010O are alcohols?O are alcohols?

1. 12. 23. 34. 45. 5


How many constitutional isomers of How many constitutional isomers of CC44HH1010O are alcohols?O are alcohols?

1. 12. 23. 34. 45. 5

SolutionSolution

63

3.5 Properties of Alkanes3.5 Properties of AlkanesCalled paraffins (low affinity compounds)

because they do not react as most chemicalsThey will burn in a flame, producing carbon

dioxide, water, and heat

64

Crude OilCrude OilThe hydrocarbons

in crude oil areSeparated by

boiling points.Heated to

higher temperatures to produce gases that can be removed and cooled.


alkane + O2 CO2 + H2O + energy

65

Combustion of AlkanesCombustion of AlkanesAlkanes 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.


66


Propane is used to provide heat forcooking or warming a room. Write abalanced equation for the completecombustion of propane.


67

Learning CheckLearning CheckPropane is used to provide heat forcooking or warming a room. Write abalanced equation for the completecombustion of propane.


SolutionSolution

C3H8 + 5O2 3CO2 + 4H2O

68

Write a balanced equation for the reaction for the complete combustion of:

heptane

ethane


69

Write a balanced equation for the reaction for the complete combustion of:

heptane C7H16.

ethane

SolutionSolution

CC77HH1616 + 11O + 11O22 7CO 7CO22 + 8H + 8H22OO

2C2C22HH66 + 7O + 7O22 4CO4CO22 + 6H + 6H22O O

70

Properties of AlkanesProperties of AlkanesThey react with Halogens like Cl2 in the

presence of light to replace H’s with Cl’s (not controlled)

71

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

72

SolutionSolutionGive 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

73

Physical PropertiesPhysical PropertiesBoiling points and melting points increase as size of alkane

increasesDispersion forces increase as molecule size increases,

resulting in higher melting and boiling points

74

3.6 Conformations of Ethane3.6 Conformations of EthaneStereochemistry concerned with the 3-D

aspects of moleculesσ bonds are cylindrically symmetricalRotation is possible around C-C bonds in

open-chain molecules

75

ConformersConformersConformation- Different arrangement

of atoms resulting from bond rotationConformations can be represented in 2

ways:

76

Torsional StrainTorsional Strain

We do not observe perfectly free rotationThere is a barrier to rotation, and some

conformers are more stable than othersStaggered- most stable: all 6 C-H bonds

are as far away as possibleEclipsed- least stable: all 6 C-H bonds are

as close as possible to each other

78

3.7 Conformations of Other Alkanes3.7 Conformations of Other AlkanesThe eclipsed conformer of propane has 3

interactions: two ethane-type H-H interactions, and one H-CH3 interaction

79

• Conformational situation is more complex for larger alkanes

• Not all staggered conformations has same energy, and not all

eclipsed conformations have same energy

Conformations of Other Alkanes

80

Conformations of ButaneConformations of ButaneAnti conformation- methyl groups are 180˚ apartGauche conformation- methyl groups are 60˚ apart

Which is the most energetically stable?

82

Steric StrainSteric StrainSteric strain- repulsive interaction occurring between atoms

that are forced closer together than their atomic radii allow

6

46

3.8 1111

44

What is the correct order of stability, starting with What is the correct order of stability, starting with the most strained, for the conformations shown the most strained, for the conformations shown below?below?

1. A B, C2. A, C, B3. B, A, C4. C, A, B5. C, B, A

CH3

H H

CH2CH3

HH3C

CH3

H HCH3

CH2CH3HCH3

H HH

CH3CH3CH2

A B C


What is the correct order of stability, starting with What is the correct order of stability, starting with the most strained, for the conformations shown the most strained, for the conformations shown below?below?

1. A B, C2. A, C, B3. B, A, C4. C, A, B5. C, B, A

CH3

H H

CH2CH3

HH3C

CH3

H HCH3

CH2CH3HCH3

H HH

CH3CH3CH2

A B C

SolutionSolution

CC66HH1414 has 5 isomers. How many of these has 5 isomers. How many of these isomers have at least one tertiary carbon?isomers have at least one tertiary carbon?

1. 02. 13. 24. 35. 4


CC66HH1414 has 5 isomers. How many of these has 5 isomers. How many of these isomers have at least one tertiary carbon?isomers have at least one tertiary carbon?

1. 02. 13. 24. 35. 4

SolutionSolution

Which statement about bond rotations around C-C Which statement about bond rotations around C-C bonds in ethane and ethylene is correct?bonds in ethane and ethylene is correct?

1. Rotation around σ bond is easy because the orbital overlap does not change with rotation.

2. Rotation around π bond is easy because there are p orbitals available in all directions of space.

3. Rotation around σ bond is very hard because the electron pairs from the adjacent bonds must pass by each other.

4. Rotation around π bond is hard because the electrons are delocalized.


Which statement about bond rotations around C-C Which statement about bond rotations around C-C bonds in ethane and ethylene is correct?bonds in ethane and ethylene is correct?

1. Rotation around σ bond is easy because the orbital overlap does not change with rotation.

2. Rotation around π bond is easy because there are p orbitals available in all directions of space.

3. Rotation around σ bond is very hard because the electron pairs from the adjacent bonds must pass by each other.

4. Rotation around π bond is hard because the electrons are delocalized.

SolutionSolution

Which of the above represents the Newman projection of Which of the above represents the Newman projection of 2-bromo-3-chlorobutane?2-bromo-3-chlorobutane?

1. a2. b3. c4. d5. e

CH3

H

H

H3C

Br

Cl

H

CH3

H

Br

CH3

Cl

Cl

CH3

H

H

Br

CH3

CH3

Cl

H3C

H

Br

H

H

CH3

Br

H3C

CH3

Cl

a) b) c) d) e)


Which of the above represents the Newman projection of Which of the above represents the Newman projection of 2-bromo-3-chlorobutane?2-bromo-3-chlorobutane?

1. a2. b3. c4. d5. e

CH3

H

H

H3C

Br

Cl

H

CH3

H

Br

CH3

Cl

Cl

CH3

H

H

Br

CH3

CH3

Cl

H3C

H

Br

H

H

CH3

Br

H3C

CH3

Cl

a) b) c) d) e)

SolutionSolution

The lowest energy conformation of decane resembles a The lowest energy conformation of decane resembles a straight rod. It is a fully stretched “zig-zag” conformation straight rod. It is a fully stretched “zig-zag” conformation with all bonds staggered and all large substituents anti to with all bonds staggered and all large substituents anti to each other. Imagine we bend this chain at carbon 5. What is each other. Imagine we bend this chain at carbon 5. What is the minimum strain that such a once-bent conformation the minimum strain that such a once-bent conformation (bent rod) must have?(bent rod) must have?

1. 3.8 kJ/mol2. 4.0 kJ/mol3. 6.0 kJ/mol4. 0.0 kJ/mol5. 11.0 kJ/mol


The lowest energy conformation of decane resembles a The lowest energy conformation of decane resembles a straight rod. It is a fully stretched “zig-zag” conformation straight rod. It is a fully stretched “zig-zag” conformation with all bonds staggered and all large substituents anti to with all bonds staggered and all large substituents anti to each other. Imagine we bend this chain at carbon 5. What is each other. Imagine we bend this chain at carbon 5. What is the minimum strain that such a once-bent conformation the minimum strain that such a once-bent conformation (bent rod) must have?(bent rod) must have?

1. 3.8 kJ/mol2. 4.0 kJ/mol3. 6.0 kJ/mol4. 0.0 kJ/mol5. 11.0 kJ/mol

SolutionSolution

What is the energy difference between the two lowest-What is the energy difference between the two lowest-energy conformations of 2,3-dimethylbutane?energy conformations of 2,3-dimethylbutane?

1. the energy of one gauche interaction2. the energy of two gauche interactions3. the energy of two H ↔ CH3 eclipsing interactions

4. the energy of three H ↔ CH3 eclipsing interactions

5. the energy of two CH3 ↔ CH3 eclipsing interactions


What is the energy difference between the two lowest-What is the energy difference between the two lowest-energy conformations of 2,3-dimethylbutane?energy conformations of 2,3-dimethylbutane?

1. the energy of one gauche interaction2. the energy of two gauche interactions3. the energy of two H ↔ CH3 eclipsing interactions

4. the energy of three H ↔ CH3 eclipsing interactions

5. the energy of two CH3 ↔ CH3 eclipsing interactions

SolutionSolution

The highest energy conformation of ethane has 12 kJ/mol of The highest energy conformation of ethane has 12 kJ/mol of strain. The two highest conformations of butane have 16 and strain. The two highest conformations of butane have 16 and 19 kJ/mol of strain, respectively. How much strain does the 19 kJ/mol of strain, respectively. How much strain does the highest energy conformation of 2,3-dimethylbutane have?highest energy conformation of 2,3-dimethylbutane have?

1. 16 kJ/mol2. 20 kJ/mol3. 26 kJ/mol4. 31 kJ/mol5. 37 kJ/mol


The highest energy conformation of ethane has 12 kJ/mol of The highest energy conformation of ethane has 12 kJ/mol of strain. The two highest conformations of butane have 16 and strain. The two highest conformations of butane have 16 and 19 kJ/mol of strain, respectively. How much strain does the 19 kJ/mol of strain, respectively. How much strain does the highest energy conformation of 2,3-dimethylbutane have?highest energy conformation of 2,3-dimethylbutane have?

1. 16 kJ/mol2. 20 kJ/mol3. 26 kJ/mol4. 31 kJ/mol5. 37 kJ/mol

SolutionSolution

3 ch241 alkanes (2)

Documents