1. Chapter 4 Chapter 4 Alkanes, Alkenes and Alkynes: Nomenclature, Conformational Analysis, and an Introduction to Synthesis

2. The branch of chemistry that deals with carbon compounds is called organic chemistry Common Elements in Organic Compounds

3.  Functional Groups  Functional Group is a group of atoms that is largely responsible for the chemical behavior of the parent molecule.  Functional group families are characterized by the presence of a certain arrangement of atoms called a functional group  A functional group is the site of most chemical reactivity of a molecule  The functional group is responsible for many of the physical properties of a molecule

4. Classification of Hydrocarbons Aliphatic hydrocarbons do not contain the benzene group, or the benzene ring. aromatic hydrocarbons contain one or more benzene rings Most organic compounds are derived from a group of compounds known as hydrocarbons because they are made up of only hydrogen and carbon.

5. 24.2 Aliphatic Hydrocarbons Alkanes –cycloalkanes - Alkene - Alkyne Alkanes have the general formula C n H 2n+2 where n = 1,2,3,… only single covalent bonds Saturated Hydrocarbons because they contain the maximum number of hydrogen atoms that can bond with the number of carbon atoms in the molecule CH 4 C2H6C2H6 C3H8C3H8 methaneethanepropane 1- Alkanes (Paraffins)

6. Nomenclature of Unbranched Alkanes The Unbranched Alkane

7. Shapes of Alkanes “Straight-chain” alkanes have a zig-zag orientation when they are in their most straight orientation.  Straight chain alkanes are also called unbranched alkanes

8.  Branched alkanes have at least one carbon which is attached to more than two other carbons

9. Structural (Constitutional) Isomers  Constitutional isomers have the same molecular formula but different connectivity of atoms.  have different physical properties (melting point, boiling point, densities etc.). Physical Contents of the Hexane Isomers

10.  The number of constitutional isomers possible for a given molecular formula increases rapidly with the number of carbons Number of Alkane Isomers

11. Q: Which of these species are structural isomers of C 6 H 14 ? A. I and II B. I and III C. II and III D. II and IV E. III and IV

12. The first 10 Unbranched Alkanes

13. Nomenclature of Unbranched Alkyl Groups Nomenclature of Unbranched Alkyl Groups The unbranched alkyl groups are obtained by removing one hydrogen from the alkane and named by replacing the -ane of the corresponding alkane with -yl AlkaneAlkayl GroupAbberiviation

14. 14 IUPAC: International Union of Pure and Applied Chemistry Alkanes Nomenclature each name consist of 3 parts  prefix indicates position (1,3,…etc.), number (di, tri, tetra …etc.) and type of branches (alkyl or substituent groups)  parent indicates the length of the longest carbon chain or ring  suffix indicates the type of hydrocarbon (-ane, -ene, -yne) parentsuffixprefix What family? What substituents? How many carbons?

15. Nomenclature of Branched-Chain Alkanes (IUPAC) Locate the longest continuous chain of carbons; this is the parent chain and determines the parent name. Number the longest chain beginning with the end of the chain nearer the substituent Designate the location of the substituent CH 3 CH 2 CHCH 2 CH 3 1234567 4-methylheptane

16. When two or more substituents are present, give each substituent a number corresponding to its location on the longest chain Substituents are listed alphabetically CH 3 CH CH 3 Br 1234 NO 2 2-bromo-3-nitrobutane CH 2 CHCH 3 NH 2 1234 Cl 1-amino-3-chlorobutane

17. When two or more substituents are identical, use the prefixes di-, tri-, tetra- etc. When two chains of equal length compete to be parent, choose the chain with the greatest number of substituents When branching first occurs at an equal distance from either end of the parent chain, choose the name that gives the lower number at the first point of difference

18. What is the IUPAC name of the following compound? 1234567 8 CH 3 CHCH 2 CHCH 2 CH 3 C2H5C2H5 CH 2 CH 3 4-ethyl-2-methyloctane What is the structure of 2-ethyl-4-methylhexane? 123456 CH 3 CHCH 2 CHCH 2 CH 3 MeEt

19. Nomenclature of Branched Alkyl Chains  Two alkyl groups can be derived from propane  Four groups can be derived from the butane isomers

20.  The neopentyl group is a common branched alkyl group  Examples

21. Write the structural formula of the following compounds 1 2 Problem 4.23 p.182 (a), (d), (d), (e), (g), (h), (i), (j), (l), (m), (n)

22. Give the IUPAC name of the following compounds 1 2 Problem 4.24 p. 182 (a), (d), (e)

23. Classification of Hydrogen Atoms Hydrogen atoms take their classification from the carbon they are attached to. 1° Hydrogen atoms Primary Hydrogen atoms 2° Hydrogen atoms Secondary Hydrogen atoms 3° Hydrogen atoms Tertiary Hydrogen atoms

24. Classify each color of carbon atoms in the following compounds:

25. Nomenclature of Alkyl Halides  In IUPAC nomenclature halides are named as substituent on the parent chain Halo and alkyl substituents are considered to be of equal ranking.  In common nomenclature the simple haloalkanes are named as alkyl halides Common nomenclature of simple alkyl halides is accepted by IUPAC and still used.

26. IUPAC Substitutive Nomenclature  An IUPAC name may have up to 4 features: locants, prefixes, parent compound and suffixes  Numbering generally starts from the end of the chain which is closest to the group named in the suffix

27. 2- Cycloalkanes Alkanes whose carbon atoms are joined in rings are called cycloalkanes. They have the general formula C n H 2n, where n = 3,4,… The The prefix cyclo- is added to the name of the alkane with the same number of carbons

28. Nomenclature of Cycloalkanes A.When one substituent is present it is assumed to be at position one and is not numbered. B.When two alkyl substituents are present the one with alphabetical priority is given position 1 ×

29. C.Numbering continues to give the other substituent the lowest number D.Hydroxyl has higher priority than alkyl and is given position 1. ×

30. E.If a long chain is attached to a ring with fewer carbons, the cycloalkane is considered the substituent.

31. Bicyclic compounds  Bicyloalkanes contain 2 fused or bridged rings.  The alkane with the same number of total carbons is used as the parent and the prefix bicyclo- is used. Bicyclo[2.2.1]heptane

32.  The number of carbons in each bridge is included in the middle of the name in square brackets Bridged Fused

33. Give the name of the following compounds: 2-Clorobicyclo[1.1.0]butanebicyclo[3.2.1]octane bicyclo[3.3.2]decane9-Bromoobicyclo[4.2.1]nonane

34. Write the structural formula of the following: 7,7-Dichlorobicyclo[2.2.1]heptane bicyclo[3.2.0]heptane

35. Nomenclature of Alkenes and Cycloalkenes  Alkenes (Olefins)  Alkenes have the general formula C n H 2n where n = 2,3,…  contain at least one carbon-carbon double bond  Alkenes are named by finding the longest chain containing the double bond and changing the name of the corresponding parent alkane from -ane to -ene  The compound is numbered to give one of the alkene carbons the lowest number × ×

36.  The double bond of a cylcoalkene must be in position 1 and 2 × ×  Compounds with double bonds and alcohol hydroxyl groups are called alkenols, The hydroxyl is the group with higher priority and must be given the lowest possible number

37.  Two groups which contain double bonds are the vinyl and the allyl groups.

38. Nomenclature of Alkynes Alkynes have the general formula C n H 2n-2 where n = 2,3,4,… Contain at least one C  C triple bond. Alkynes are named by finding the longest chain containing the triple bond and changing the name of the corresponding parent alkane from -ane to -eye The long chain is number to give the carbon atoms of the triple bond the lower possible number. ethyne (acetylene ) 4-methyl-1-pentyne 123 4 5 2-methyl-3-hexyne 2,5-dimethyl-3-hexyne

39. Compounds with triple bonds and alcohol hydroxyl groups: The hydroxyl is the group with higher priority and must be given the lowest possible number. 1,1-dichloro-2-butyne Or 1,1-dichlorobut-2-yne 1-bromo-4,4-dimethyl-1-pentyne Or 1-bromo-4,4-dimethylpent-1-yne 2-methyl-4-pentyne-2-ol Or 2-methylpent-4-yne-2-ol 2-methyl-3-butyne-1-ol Or 2-methylbut-3-yne-1-ol

40. Compounds with triple and double bonds, the double bond is given the lower number. 1-penten-4-yne Or pent-1-en-4-yne

41. Physical Properties of Alkanes and Cycloalkanes  Boiling points of unbranched alkanes increase smoothly with number of carbons.  Melting points increase in an alternating pattern according to whether the number of carbon atoms in the chain is even or odd.

42. If we examine the unbranched alkenes in the latest figures, we notice that:  Each alkane differs from the preceding alkane by one methylene group (-CH 2 ).  Each member differs from the next one by a constant unit, is called a homologous series.  At room temperature (25°C) and (1 atm) pressure: The C 1 -C 4 homologous series of unbranched alkanes are gases. The C 5 -C 17 unbranched alkanes are liquids. The C 18 -more unbranched alkanes are solids.

43. Steriochemical Structure of Ethane Fischer Projection Ball and stick model dash-wedge structure Newman Projection

44. Stereo Isomerism 2- Conformational Isomerism  Ethane has relatively free rotation around the carbon-carbon bond.  The drawing to the right is called a Newman projection  The staggered conformation has C-H bonds on adjacent carbons as far apart from each other as possible. staggered conformation

45. Staggered conformation هيئة متبادلة “dash-wedge” Projection“sawhorse” Projection“Newman” Projection

46.  The eclipsed conformation has all C-H bonds on adjacent carbons directly on top of each other eclipsed conformation

47. Eclipsed conformation هيئة منكسفة “dash-wedge” Projection “sawhorse” Projection “Newman” Projection

48.  The potential energy diagram of the conformations of ethane shows that the staggered conformation is more stable than eclipsed by 12 kJ mol-1 Conformation analysis of Ethane more stable Low energy less stable High energy

49.  Rotation around C 2 -C 3 of butane gives six important conformations  The gauche conformation is less stable than the anti conformation by 3.8 kJ mol -1 because of repulsive Van der Waals forces between the two methyl groups. Conformation analysis of Butane more stable less stable

50. The Relative Stabilities of Cycloalkanes: Ring Strain  Heats of combustion per -CH 2 unit reveal cyclohexane has no ring strain and other cycloalkanes have some ring strain

51.  Experiment have shown that cyclohexane is the most stable cycolalkane.  Cyclopropane and cyclobutane are much less stable.  This difference in relative stability is due to ring strain, which comprises by:  Angle strain is caused by bond angles different from 109.5 o  Torsional strain is caused by eclipsing C-H bonds on adjacent carbons The Relative Stabilities of Cycloalkanes: Ring Strain in Cyclopropane and Cyclobutane

52. Ring Strain in Cyclopropane  Cyclopropane has both high angle and torsional strain.  According to the high strain and low stability, cyclopropane not exist in nature.  Cyclopropane prepared for the first time in labortary 1880.  The carbon atoms of alkane are sp 3 hybridized, and the angle of tetrahedral is 109.5°.  In cyclopropane the internal angle of the regular triangle must be 60°, but it found 115°.

53. Ring Strain in Cyclobutane  Cyclobutane dos not exist free in nature, because of its high strain and low stability.  Cyclobutane prepared for the first time in labortary.  Cyclobutane also has considerable angle strain.  The internal angles are 88° less than the normal tetrahedral angle.  The cyclobutane ring is not planer, but is slightly fold causing high torsional strain.  If cyclobutane ring is planer, it will show little angle strain.

54. Ring Strain in Cyclopentane  Cyclopentane available naturally in oil fields.  Cyclopentane is almost as stable as cyclohexane.  The internal angles of cyclopentane are 108°,very close to the normal tetrahedral angle 109.5°.  If cyclopentane ring is planer, it will introduce torsional considerable strain, bacause all 10 C-H bonds will be eclipsed.  According to the bent conformation of cyclopentane ring, it cause some torsional strain.

55. EnvelopeHalf-chair Ring Strain in Cyclopentane  Because of the non-planer conformation of cyclopentane,slightly twisting of C-C bond occur with little change in energy.  Therefore, the molecule is flexible and shift rapidly from one conformation to the another as shown.  Cyclopentane has little torsional and angle strain.

56.  Cyclohexane available naturally with high abundance in oil fields.  Cyclohexane is the most stable cycloalkanes, for several reasons: It has several conformations. It has several conformations. Conformations of Cyclohexane

57. The most stable of cyclohexane is the chair conformation. The most stable of cyclohexane is the chair conformation. The chair conformation has no ring strain (angle and torsional strain). The chair conformation has no ring strain (angle and torsional strain). All bond angles are 109.5° and all C-H bonds are perfectly staggered. All bond angles are 109.5° and all C-H bonds are perfectly staggered. Chair Conformation Newman Projection of Chair Conformation

58.  heat of combustion suggests that angle strain is unimportant in cyclohexane.  tetrahedral bond angles require nonplanar geometries.

59. Chair Conformation Boat Conformation - Most stable - Less stable - 99% of cyclohexane is as chair form. - 1% of cyclohexane is as a boat form. - Large separation between H atoms at the opposite corner of C1-C4. - Short distance between H atoms at the corner of C1-C4. - All C-H bonds are staggered arrangement and the angles is closed to tetrahedral. - All C-H bonds are eclipsed arrangement caused van der Waals repulsive. - No angle and torsional strain. - No angle, but have torsional strain.

60.  The twist conformation is intermediate in stability between the boat and the chair conformation Twist Conformation

61. The Relative Energy of the Various Conformations of Cyclohexane more stable less stable

62. Substituted Cyclohexanes: Axial and Equatorial Hydrogen Atoms  Axial hydrogens are perpendicular to the average plane of the ring.  Equatorial hydrogens lie around the perimeter of the ring.  The C-C bonds and equatorial C-H bonds are all drawn in sets of parallel lines.  The axial hydrogens are drawn straight up and down.

63. Axial bonds point "north and south"Axial bonds point "north and south" 6 Bonds are axial 6 Bonds are equatorial Equatorial bonds lie along the equator.Equatorial bonds lie along the equator.

64.  Methyl cyclohexane is more stable with the methyl equatorial.  An axial methyl has an unfavorable 1,3-diaxial interaction with axial C-H bonds 2 carbons away  A 1,3-diaxial interaction is the equivalent of 2 gauche butane interactions A Conformational Analysis of Methyl Cycolhexane less stable more stable

65. Disubstitued Cycloalkanes  Can exist as pairs of cis-trans stereoisomers  Cis- groups on same side of ring  Trans- groups on opposite side of ring less stablemore stable No Steric Hindrance

66. Trans-1,4-dimethylcylohexane prefers a trans-diequatorial conformation

67. Cis-1,4-dimethylcyclohexane exists in an axial-equatorial conformation A very large tert-butyl group is required to be in the more stable equatorial position

68. Geometric Isomerism in disubstituted chair conformation of cyclohexane 1,2-disubstituents1,3-disubstituents1,4-disubstituents A A A-A trans- A E A-E cis- E E E-E trans- A A A-A cis- A E A-E trans- E E E-E cis- A A A-A trans- A E A-E cis- E E E-E trans-

69. Convert to chair conformation

70. Cl Consider each of the following conformational structures and tell whether each cis- or trans- A-E cis- E-E cis- Cl E-E trans-

71. Isomers are compounds that have the same formula but different structures Isomerism

72. Structural Isomerism 1- Skeletal Isomerism Example: Skeletal Isomerism of C 6 H 14 The structure is different but the formula is constant for all.

73. Structural Isomerism 2- Positional Isomerism Example: Positional Isomerism of C 6 H 14 O Only the position of the functional group is different.

74. Structural Isomerism 3- Functional Isomerism Example 1: Functional Isomerism of C 3 H 6 O KetoneAldehyde Example 2: Functional Isomerism of C 2 H 6 O Alcohol Ether The type of the functional group is different.

75. Structural Isomerism 4- Tutomeric Isomerism Example: Tutomeric Isomerism of C 5 H 8 O 2

76. Isomerism

77. Stereo isomerism 1- Geometric Isomerism Example 1: Geometric Isomerism of ClCH=CHCl  This type of isomer occurs when no free rotation is available in Alkenes and Cycloalkanes.  If two hydrogens occur on the same side of the double bond the compound is cis- (Latin word means on the same side)  If they are on opposite sides the compound is trans- (Latine word means on the opposite side) no free rotation around the double bond cis- trans-

78. Example 2: Geometric Isomerism of (CH 3 )CH=CH(CH 3 ) cis-2-butenetrans-2-butene Example 3: Geometric Isomerism of 1,3-dimethylcyclobutane cis-1,3-dimethylcyclobutanetrans-1,3-dimethylcyclobutane

79.  The (E)-(Z) System for Designating Alkene Diastereomers  Cis- and trans- terms was used to designate the stereochemistry of disubtituted alkene.  If the alkene is trisubstituted or tetrasubstituted, the terms cis- or trans- are either ambiguous or not applied at all.  Cosider the following alkene as an example:  Its impossible to decide whether of the following compounds cis- or trans- since no two identical groups available.

80.  A system that used in all cases is based on the priorities of substituted groups called the (E)-(Z) System.  If the group of highest priority on one carbon is on the same side as the group of highest priority on the other carbon the double bond is Z (Zusammen)  If the highest priority groups are on opposite sides the alkene is E (Entgegen)

81. Using the (E)-(Z) System, give the IUPAC names for each of the following compounds:

82. Think about this case: No cis- or trans- isomers No (E )or (Z ) system cis- isomers (Z ) system trans- isomers (E ) system (Z )system trans- isomers (E )system cis- isomers (Z )system

83. Using the (E)-(Z) System, give the IUPAC names for each of the following compounds: (E ) 1-bromo1-chloro-1-pentene (E ) 2-bromo1-chloro-1-iodo-1-butene (Z ) 3,4-dimethyl-2-hexene

84.  Relative Stabilities of Alkenes  Generally cis- alkenes are less stable than trans- alkenes because of steric hinderance (crowding by the adjacent alkyl groups). This effect can be measured quantitatively by comparing thermodynamic data from experiments involving the alkenes with related structures, as we shall see below: cis- trans- 84

87. Enantiomers: Enantiomers: stereoisomers whose molecules are nonsuperposable mirror images Diastereomers Diastereomers: stereoisomers whose molecules are not mirror images of each other  Example: cis- and trans- double bond isomers  Example: cis- and trans- cycloalkane isomers

88. Stereo Isomerism 3- Optical Isomerism What is Optical Activity ? Optical Activity is measured by the degree of rotation of plane-polarized light passing through a chiral medium.

89. Polarimeter is an instrument used to measure the optical rotation of various substances on plane-polarized light. optical active substances in Polarimeter tube light source unpolarized light polarized light rotated polarized light polarizer Analyzer prism

90. Chiral molecule H A molecule with a single tetrahedral carbon bonded to four different groups will always be chiral H A molecule with more than one tetrahedral carbon bonded to four different groups is not always chiral H Switching two groups at the tetrahedral center leads to the enantiomeric molecule in a molecule with one tetrahedral carbon * *

91. (c) Example: 2-butanol  2-butanol is a chiral molecule  I and II are mirror images of each other (figures a and b)  I and II are not superposable and so are enantiomers (figure c) (b) (a) **

92. Example: 2-propanol  Not chiral

93. R ectus S inister ** * *  Nomenclature of Enantiomers: The R,S System Also called the Cahn-Ingold-Prelog system The four groups attached to the stereogenic (chiral) carbon are assigned priorities from highest (a) to lowest (d) Priorities are assigned as follows  Atoms directly attached to the stereogenic center are compared  Atoms with higher atomic number are given higher priority  If priority cannot be assigned based on directly attached atoms, the next layer of atoms is examined  If the groups descend in priority (a,b then c) in clockwise direction the enantiomer is R  If the groups descend in priority in counterclockwise direction the enantiomer is S

94. Example 1 3 2 4 (R) 2-butanol

95. How to assign (R) and (S) configurations? R configuration 1 1 2 2 33 44 S configuration R configuration

96. Indicate the R or S configuration

97.  Rotation of the plane of polarized light in the clockwise sense is taken as positive (+)  Rotation in the counterclockwise sense is taken as a negative (-) rotation.  Older terms for positive and negative rotations were dextrorotatory and levorotatory, from the Latin prefixes dextro- ("to the right") and levo- ("to the left"), respectively What is the meaning of (+) or (-) and d- l- ??

98.  Properties of Enantiomers: Optical Activity Enantiomers have almost all identical physical properties (melting point, boiling point, density) However enantiomers rotate the plane of plane-polarized light in equal but opposite directions

99. The specific rotation of the two pure enantiomers of 2-butanol are equal but opposite There is no straightforward correlation between the R,S designation of an enantiomer and the direction [(+) or (-)] in which it rotates plane polarized light Racemic mixture Racemic mixture  A 1:1 mixture of enantiomers  No net optical rotation  Often designated as (+) RS

100.  Reduction of Alkyl Halides Preparation of Alkanes

101.  Alkylation of Terminal Alkynes Alkynes can be subsequently hydrogenated to alkanes

103.  Substitution (Free Radicals Halogenation) Reactions of Alkanes

104. Mechanisms of Free Radicals Halogenation

105.  Freund Reaction 1,3-dibromopropanecycolpropane 1,4-dibromobutanecycolbutane

106.  Hydrogenation: Reactions of Alkanes