Chapter 2.Chapter 2. Alkanes and CycloalkanesAlkanes and Cycloalkanes

.Chapter 2.Chapter 2 Alkanes and CycloalkanesAlkanes and Cycloalkanes

Based on: McMurry’s Fundamental of Organic Chemistry, 4th edition, Chapter 2

2

Families of Organic Compounds

Organic compounds can be grouped into families by their common structural features

We shall survey the nature of the compounds in a tour of the families in this course

This chapter deals with alkanes, compounds that contain only carbons and hydrogens, all connected exclusively by single bonds

3

2.1 Functional Groups

Functional group - an atom or group of atoms within a molecule that shows a characteristic set of physical and chemical properties

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

4

Double Bond as Functional Group

5

Survey of Functional Groups

Table 2.1 (page 46 and 47) lists a wide variety of functional groups that you should recognize

As you learn about them in each chapter it will be easier to recognize them

The functional groups affect the reactions, structure, and physical properties of every compound in which they occur

6

I. Classes of Organic Compounds

Hydrocarbons (C & H only) Heteroatomic compounds

aliphatic aromatic

alkanes

alkenes

alkynes

cyclic compounds

alcohols

ethers

aldehydes

ketones

carboxylic acids

esters

amines

amides

C C

C C

C C

R OH

R O R'

R C

O

H

R C

O

R'

R C

O

OH

R C

O

OR'

R C

O

NH2

R NH2

7

Functional groups are important for three reason; they are1. the units by which we divide organic compounds

into classes

2. the sites of characteristic chemical reactions

3. the basis for naming organic compounds

8

Types of Functional Groups: Multiple Carbon–Carbon Bonds Alkenes have a C-

C double bond Alkynes have a C-C

triple bond Arenes (or aromatic

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

9

Functional Groups with Carbon Singly Bonded to an Electronegative Atom Alkyl halide: C bonded to halogen (C-X) Alcohol: C bonded O of a hydroxyl group (COH) Ether: Two C’s bonded to the same O (COC) Amine: C bonded to N (CN) Thiol: C bonded to SH group (CSH) Sulfide: Two C’s bonded to same S (CSC) Bonds are polar, with partial positive charge on C (+) and

partial negative charge () on electronegative atom

10

11

12

2.2 Alkanes and Alkane Isomers Alkanes: Compounds with C-C single bonds and C-H bonds only

(no functional groups)

The formula for an alkane with no rings (acyclic) must be CnH2n+2 where the number of C’s is n

Alkanes are saturated with hydrogen (no more can be added) (saturated hydrocarbon)

They are also called aliphatic compounds (aleiphas=fat)

13

A “saturated” fat (glyceryl stearate):

14

HydrocarbonsHydrocarbonsHydrocarbonsHydrocarbons

AromaticAromaticAromaticAromaticAliphaticAliphaticAliphaticAliphatic

15

HydrocarbonsHydrocarbonsHydrocarbonsHydrocarbons

AromaticAromaticAromaticAromaticAliphaticAliphaticAliphaticAliphatic

AlkanesAlkanesAlkanesAlkanes AlkynesAlkynesAlkynesAlkynesAlkenesAlkenesAlkenesAlkenes

16

HydrocarbonsHydrocarbonsHydrocarbonsHydrocarbons

AliphaticAliphaticAliphaticAliphatic

AlkanesAlkanesAlkanesAlkanes

Alkanes are hydrocarbons in which all of the bonds are single bonds.

CC CCHH HH

HH HH

HH HH

• Acyclic alkanes have the molecular formula CnH2n+2. They are also called saturated hydrocarbons because they have the maximum number of hydrogen atoms per carbon.

• Cycloalkanes contain carbons joined in one or more rings. Because their general formula is CnH2n,(n = 3 or more) they have two fewer H atoms than an acyclic alkane with the same number of carbons.

AlkanesRecall that alkanes are aliphatic hydrocarbons having C—C and C—H bonds. They can be categorized as acyclic or cyclic.

Cyclic Alkanes

Acyclic Alkanes

CH3H3CC

CH3H3C

18

Sources of AlkanesSources of Alkanes

Natural gas 90-95% methane Petroleum - mixture

gases gasoline, kerosene( سفید (نفت fuel oil( کوره (نفت lubricating oils asphalt

Coal ( سنگ (ذغال

Refining crude petroleum into usable fuel and other petroleum products. (a) An oil refinery. At an oil refinery, crude petroleum is separated into fractions of similar boiling point by the process of distillation. (b) Schematic of a refinery tower. As crude petroleum is heated, the lower-boiling, more volatile components distill first, followed by fractions of progressively higher boiling point.

19

20

21

پاالیشگاه در مداوم تقطیر از استفاده تولید با زیر مواد هامی شود:

گاز متان و اتان گاز ، پاالیشگاه سوخت و پروپان بعنوانواحدهای بوتان خوراک و مایع گاز ، پتروشیمی بعنوان

واحدهای خوراک بعنوان سنگین نفتهای و موتور بنزینتهیه برای کاتالیستی آروماتیسیته بنزین تبدیل درجه با

حاللها ، سفید ، باالتر سنگین ، نفت و سبک جت ، سوختگاز واحدهای ، نفت و هیدروکراکینگ واحدهای خوراک

سازی کوره ، روغن آسفالتها و نفت . انواع

22

و تراکتورها اغلب سوختدر استفاده مورد ماشین های

موتورهای همچنین و کشاورزییا کروزون از اغلب هواپیماها جت

سفید .می باشد نفت

از سوخت بعنوان دیزل موتورهای ( استفاده ( گازوئیل گاز نفت

می نمایند

کوره جسم نفت یک مازوت یاحرارتی قدرت با احتراق قابل

بخوبی 10500 که بوده کالریجانشین سنگ می تواند گردد زغال

دود بدون تقریبا آن سوختن ومی گیرد . انجام

23

In cracking, high molecular weight fractions and catalysts are heated to the point where the carbon-carbon bonds break. Products of the reaction include alkenes and alkanes of lower molecular weight than were present in the original fraction.

alkane C13H28(l) alkane C8H18(l) + alkene C2H4(g) + alkene C3H6(g)

24

آلکانها : دوم آلکانها : فصل دوم فصل

آزمایشگاهی آزمایشگاهی تهیه تهیه::آلکانهاآلکانها

و -1 -1 ها الکن و هیدروژناسیون ها الکن هیدروژناسیونها ها الکین الکین

اسیدها -2 -2 زدائی اسیدها کربوکسیل زدائی : :کربوکسیل

CnH2n + H2 CnH2n+2

CnH2n-2 + 2H2 CnH2n+2

catalyst

catalyst

H2C CH2 + H2 H3C CH3

C C

H

H

H

H

H H

catalyst

C C

H

H

H

H

H H

catalyst

C C

H

H

H

H

H H

catalyst

C C

H

H

H

H

H H

catalyst

RCOOH + NaOH RCOONa + H2O

RCOONa + NaOH Na2CO3 + RH

R C

O

OH + NaOH R C

O

O_

Na+ + H2O

R C

O

O_

R- + CO2H2O

RH + H2CO3

NaOHNa2CO3

R C

O

Oo

RCOO- Na+ RCOO- + Na+

RCOO- RCOO o + e-

R C

O

O R C

O

O

Ro C

O

O+

Ro Ro+ R-R

25

Names of Small HydrocarbonsParent names:CH4 methane n-C11H24 undecaneCH3CH3 ethane n-C12H26 dodecane CH3CH2CH3 propane n-C13H28 tridecane CH3(CH2)2CH3 butane n-C14H30 tetradecaneCH3(CH2)3CH3 pentane ¦CH3(CH2)4CH3 hexane n-C20H42 icosanen-C7H16 heptane n-C30H62 triacontanen-C8H18 octane n-C40H82 tetracontanen-C9H20 nonane ¦n-C10H22 decane etc.

26

Alkane Isomers:

CH4 = methane, C2H6 = ethane, C3H8= propane

The molecular formula of an alkane with more than three carbons can give more than one structure.When we get to Butane, C4H10, we find that there are two different structures that can share the same formula

C4 (butane) = butane and isobutane

C5 (pentane) = pentane, 2-methylbutane (isopentane), and 2,2-dimethylpropane (neopentane)

Same Formula

Different Structure

• All C atoms in an alkane are surrounded by four groups, making them sp3 hybridized and tetrahedral, and all bond angles are 109.50.

• The three-carbon alkane CH3CH2CH3, called propane, has a molecular formula C3H8. Note in the 3-D drawing that each C atom has two bonds in the plane (solid lines), one bond in front (on a wedge) and one bond behind the plane (on a dashed line).

3-D Representation of Alkanes

HC

C

H

H H

H

H

3-D Representation of Ethane

C2H6Ethane

CH3CH3

HC

C

H

H H

H

CH

HH

3-D Representation of Propane

C3H8Propane

CH3CH2CH3

• There are two different ways to arrange four carbons, giving two compounds with molecular formula C4H10, named butane and isobutane.

• Butane and isobutane are Constitutional isomers, two different compounds with the same molecular formula.

Branched & Straight-Chain Alkanes

HC

C

H

HH

H

CC

H

HH

H

H

3-D Representation of Butane

HC

C

H

CH3H

H

CH

H H

3-D Representation of Isobutane

29

Alkane Isomers

30

Condensed Structures of Alkanes

• We can represent an alkane in a brief form or in many types of extended form

• A condensed structure does not show bonds but lists atoms, such as – CH3CH2CH3 (propane)– CH3(CH2)2CH3

neopentane(2,2-dimethylpropane)

(CH(CH33))44CC

31

Alkane Isomers

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

The longest continuous chain of carbons is called the parent chain

CH3

CH2CH

CH3

CH3

CH3

CH2CH2

CH2CH3

32

Constitutional (Structural) Isomers

Isomers that differ in how their atoms are arranged in chains are called constitutional (or structural) isomers

Structural isomers ساختمانی ساختمانی ایزومرهای are ایزومرهایmolecules with the same chemical formulas but different molecular structures - different “connectivity”.

Compounds other than alkanes can also be Structural isomers of one another

They must have the same molecular formula to be isomers

33

Constitutional Isomers

34

Ea=2.9 kcal/molEa=2.9 kcal/mol

در مختلفی آرایشهای سیگما محور حول چرخش اثر در در مختلفی آرایشهای سیگما محور حول چرخش اثر دربه . و کانفورماسیون پدیده این به شوند می حاصل به . ملکولها و کانفورماسیون پدیده این به شوند می حاصل ملکولها

می ماسیونی کانفور های ایزومر آرایشها این از کدام می هر ماسیونی کانفور های ایزومر آرایشها این از کدام هر..گویندگویند

جداسازی قابل ایزومرها اغلب خالف بر مرها جداسازی کانفور قابل ایزومرها اغلب خالف بر مرها کانفورهستند. یکدیگر به تبدیل حال در دایما زیرا هستند. نیستند یکدیگر به تبدیل حال در دایما زیرا . .نیستند

C C C C

H

H HH

HHH

H

H

H

HH

های های ایزومر ایزومرکنفورماسیونی :کنفورماسیونی :

35

می دست به زیر معادله طبق گوناگون های بندی صورت جمعیتآید.

G° = -RT ln Keqpe

rcen

tage

36

Gauche Anti Ho = -0.8 kcal/mol

S° = -R ln w , T = 298 K , R = 1.987 cal/mol.K

w: Number of states

S° = -R ln 2 = -1.38 cal

H H

CH3

H CH3

HH H

CH3

H H

CH3

H H

CH3

H3C H

H

Gauche Anti Gauche

37

G° = H° - TS°

G° = -0.8 x 1000 – 298(-1.38)

G° = -388.8 cal= -0.39 kcal

G° = -RT ln Keq

Keq = 1.9

9.2

9.1

]anti[]gauche[

]anti[

1

9.1

]gauche[

]anti[Keq

34]gauche%[66]anti%[

at 298 K

38

2.3 Alkyl Groups Alkyl 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

39

Alkyl Groups

40

41

Types of Alkyl groups 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)

• Carbon atoms in alkanes and other organic compounds are classified by the number of other carbons directly bonded to them.

Types of Carbons in Alkanes

• Hydrogen atoms are classified as primary (10), secondary (20), or tertiary (30) depending on the type of carbon atom to which they are bonded.

Types of Hydrogens in Alkanes

44

Types of Functional groups

45

Types of Hydrogens:

46

2.4 Naming Alkanes: IUPAC

Compounds are given systematic names by a process that uses:

47

1. Find the Parent: longest continuous carbon chain2. Number the atoms in the chain Number the chain so that the substituent gets the

lowest possible number.3. Identify & number the substituents If two or more substituents are the same, the

prefixes “di,” “tri,” and “tetra” are used to indicate how many identical substituents the compound has.

Substituents are listed in alphabetical order.4. Write the name (A number and a word are

separated by a hyphen; numbers are separated by a comma)

Naming Branched-Chain Alkanes

Naming Branched-Chain Alkanes

48

1. Find the Parent: longest continuous carbon chain

49

2. Number the atoms in the chain•number from the end closest to substituent

50

3. Identify & number the substituents

51

4. Write the namecombine number and name of substituent with parent name, separating with hyphen

52

di, tri, tetra, sec, and tert are ignored in alphabetizing.

iso, neo, and cyclo are not ignored in alphabetizing.

Additional points to keep in mind...

Additional points to keep in mind...

53Copyright© 1999, Michael J. Wovkulich. All rights

reserved.

The correct alphabetical order of alkyl groups is: butyl, sec-butyl, tert-butyl, ethyl, isobutyl, isopropyl, methyl, and propyl.

5-tert-butyl-4-isopropylnonane

4-isopropyl-5-tert-butylnonane

CH3CHCH3

CH3

CH3CCH3

CH3CH2CH2CH2CHCHCH2CH2CH3

54Copyright© 1999, Michael J. Wovkulich. All rights

reserved.

Ignore the prefixes di-, tri-, etc. when arranging alkyl group names alphabetically.

4-ethyl-2,3-dimethylheptane

2,3-dimethyl-4-ethylheptane

CH3CHCHCHCH2CH2CH3

CH3

CH3

CH2CH3

55

When both directions lead to the same lowest number for one of the substituents, the direction is chosen that gives the lowest possible number to one of the remaining substituents.

Additional points to keep in mind...

Additional points to keep in mind...

56

If a compound has two or more chains of the same length, the parent hydrocarbon is the chain with the greatest number of substituents.

Additional points to keep in mind...

Additional points to keep in mind...

Sub-Rules for IUPAC Nomenclature 1. If there are two or more longest chains of equal length, the one having

the largest number of substituents is chosen. 2. If both ends of the root chain have equidistant substituents:          (i)   begin numbering at the end nearest a third substituent, if one is present.         (ii)   begin numbering at the end nearest the first cited group (alphabetical order).

573-ethyl-2,2,5-trimethylhexane

58

the carbon that is attached to the parent hydrocarbon is always the number 1 carbon of the substituent.

Names such as “isopropyl,” “sec-butyl,” and “tert-butyl” are acceptable substituent names in the IUPAC system of nomenclature, but systematic substituent names are preferable.

59

Some substituents have only a systematic name.

60

CH3 CH2 CH2 CH2 C CH2 CH2 CH2 CH3

C

CH2 CH2 CH3

CH3

CH2CH2 CH3CH3

This Should Be FunThis Should Be Fun

1 2 3

1 2 3 4 5 6 7 8 9

5-(1-Ethyl-1-methylpropyl)-5-propylnonane

61

CH2CH2

CH2CH

CH2CH3 C

CH2CH2

CH2CH2

CH2CH3

CH3

CCH3 CH2

CH3 CH2 CH3

CH3

Good Luck!Good Luck!

3-ethyl-7-(1,1-Dimethylbutyl) -7-methyldodecane

62

CH2CH2

CH2CH

CH2CH3 C

CH2CH2

CH3

CH2CH3

CH3

CCH3 CH3

CH3

name this two ways -- (the name this two ways -- (the complex group)complex group)

3-ethyl-7-(1,1-dimethylethyl)-7-methyldecane

7-tert-butyl-3-ethyl-7-methyldecane

63

64

2.5 Properties of Alkanes

Called paraffins (low affinity compounds) because they are relatively unreactive

They will burn in a flame, producing carbon dioxide, water, and heat

CH4 + 2 O2 → CO2 + 2 H2O + heat

ΔH° = –803 kJ mol–1

65

HEATS OF COMBUSTION

Heat of combustion: the enthalpy change for the complete oxidation of a compound

⇒ for a hydrocarbon means converting it to CO2 and water.

1) For methane, the heat of combustion is –803 kJ mol–1 (–191.9 kcal mol–1):

2) Heat of combustion can be used to measure relative stability of isomers.

CH4 + 2 O2 → CO2 + 2 H2O + heat

66

Heats of combustion show that isobutane is more stable than butane by 9 kJ mol–1.

67

68

Solubility of AlkanesSolubility of Alkanes alkanes are nonpolar and are hydrophobic

“water hating” because they do not dissolve in water.

Densities of AlkanesDensities of Alkanes alkanes have densities around 0.7 g/mL

Therefore a mixture of an alkane (such as Therefore a mixture of an alkane (such as gasoline or oil) and water quickly separates gasoline or oil) and water quickly separates into two phases, with the alkane on top.into two phases, with the alkane on top.

2.5 Properties of Alkanes

69

2.5 Properties of Alkanes

They react with Cl2 in the presence of light to replace H’s with Cl’s (not easily controlled)

70

Physical Properties Boiling points and melting points increase as

size of alkane increases Forces between molecules (temporary dipoles,

dispersion) are weak

71

Physical Properties of Alkanes

Intermolecular attractions: London dispersion forces (weak)

b.p. CH4 -160ºCC2H6 -89C3H8 -42n-C4H10 -0.4n-C5H10 36

Branching: lowers b.p.

-0.4°C -10.2°C

36°C 28°C 9°C

vs

greater surface areafor attraction

72

Physical Properties

73

2.6 Cycloalkanes

Cycloalkanes are alkanes that have carbon atoms that form a ring (called alicyclic compounds)

Simple cycloalkanes are rings of CH2 units, (CH2)n, or CnH2n

Structure is shown as a regular polygon with the number of vertices equal to the number of C’s (a projection of the actual structure)

74

2.6 Cycloalkanes

75

22_499

C C

C

109.5

60

No "head-on"overlap of atomic orbitals

(b)(a)

76

HEATS OF COMBUSTION OF CYCLOALKANES

Heats of Combustion and ring Strain of Cycloalkanes

77

Complex Cycloalkanes

Naturally occurring materials contain cycloalkane structures

Examples: chrysanthemic acid (cyclopropane),

prostaglandins (cyclopentane),

steroids (cyclohexanes and cyclopentane)

78

Complex Cycloalkanes

79

Properties of Cycloalkanes

Melting points are affected by the shapes and the way that crystals pack so they do not change uniformly

80

1. Cycloalkanes with only one ring: 1) Substituted cycloalkanes: alkylcycloalkanes,

halocycloalkanes, alkylcycloalkanols 2) Number the ring beginning with the

substituent first in the alphabet, and number in the direction that gives the next substituent the lower number possible.

3) When three or more substituents are present, begin at the substituent that leads to the lowest set of locants.

81

Isopropylcyclohexane

Chlorocyclopentane

2-Methylcyclohexanol

82

Number the substituents & write the name:

83

Examples:

84

2.7 Naming Cycloalkanes

Count the number of carbon atoms in the ring and the number in the largest substituent chain. If the number of carbon atoms in the ring is equal to or greater than the number in the substituent, the compound is named as an alkyl-substituted cycloalkane

85

1. Find the parent:

or butylcyclopropane

86

Problem 2.15: IUPAC names?

87

Stereoisomers

Compounds with atoms connected in the same order but which differ in three-dimensional orientation, are stereoisomers

) بندی پیکر در فضایی های ایزومر .configuration (تفاوت آنهاست

The terms “cis” and “trans” should be used to specify stereoisomeric ring structures.

Recall that constitutional isomers have atoms connected in different order.

88

2.8 Cis-Trans Isomerism in Cycloalkanes

Rotation about C-C bonds in cycloalkanes is limited by the ring structure

Rings have two “faces” and substituents are labeled as to their relative facial positions

There are two different 1,2-dimethyl-cyclopropane isomers, one with the two methyls on the same side

(cis) of the ring and one with the methyls on opposite sides (trans)

89

Stereoisomers

90

Practice Prob. 2.4: Name?

91

Problem 2.18: IUPAC Name?

92

اكتان عدد بنزین خاصیت نشان مهمترین كه است آن اكتان عدد

زود افنجار برابر در بنزین مقاومت میزان هنگام دهندهباعث موتور کاربوراتوردر كه موتور است به زدن ضربه

. شود می مخلوط به نسبت عدد پنتان- 4 ، 2 ، 2این متیل ، تری

( .هپتان -nو ایزومراکتان( شود می گیری اندازه وجود اكتان عدد بیان برای مختلفی قراردادی معیارهای

های سوخت استفاده مورد سیستم به بسته بنابراین دارد. باشند داشته متفاوت اكتان اعداد است ممكن مشابه

CH3(CH2)5CH3 CH3CCH2CHCH3

CH3

CH3 CH3

Heptane (octane rating 0)

2,2,4-Trimethylpentane (octane rating 100)

93

Octane rating: the quality of the gasoline percent 2,2,4-trimethylpentane (isooctane) in a mixture of

isooctane and heptane that has equivalent antiknock properties

Typical "octane booster" gasoline additives include MTBE (methyl tertiary butyl ether), ETBE, isooctane and toluene. Lead in the form of tetra-ethyl lead was once a common additive, but since the 1970s, its use in most of the industrialised world has been restricted, and its use is currently limited mostly to aviation gasoline.