Chapter 24From Petroleum to Pharmaceuticals 24.1 Petroleum Refining and the Hydrocarbons 24.2 Functional Groups and Organic Synthesis 24.3 Pesticides and Pharmaceuticals IR Tutor and Infrared Spectroscopy 1

Hydrocarbons Aliphatic Aromatic 2

Hydrocarbons Aliphatic Aromatic Alkanes Alkenes Alkynes 2

Alkanes are hydrocarbons in which all of the bonds are single bonds. Aliphatic C H Alkanes 2

Alkenes are hydrocarbons that contain a carbon-carbon double bond. Aliphatic C H Alkenes 2

Alkynes are hydrocarbons that contain a carbon-carbon triple bond. Aliphatic Alkynes HC CH 2

Hydrocarbons The most common aromatic hydrocarbons are those that contain a benzene ring. Aromatic H 2

Reactive Sites in Hydrocarbons The Functional Group Concept 7

IR spectroscopic characteristics Functional Group a structural unit in a molecule responsible for its characteristic chemical behavior and its IR spectroscopic characteristics 8

functional group is a hydrogen atom the reaction that takes place is Alkanes R—H R—X functional group is a hydrogen atom the reaction that takes place is termed a substitution one of the hydrogens is substituted by some other atom or group, X 9

functional group is a hydrogen Alkanes R—H R—X functional group is a hydrogen the reaction that takes place is substitution one of the hydrogens is substituted by some other atom or group C H C H Cl + Cl2 + HCl 9

Functional Groups in Hydrocarbons alkanes RH alkenes RH, double bond alkynes RH, triple bond aromatics ArH, double bond 10

Some Key Functional Groups 11

Families of organic compounds and their functional groups Alcohols ROH Alkyl halides RX (X = F, Cl, Br, I) Amines primary amine: RNH2 secondary amine: R2NH tertiary amine: R3N Ethers ROR 12

Many classes of organic compounds contain a carbonyl group Acyl group 15

Many classes of organic compounds contain a carbonyl group H Carbonyl group Aldehyde 15

Many classes of organic compounds contain a carbonyl group Ketone 15

Many classes of organic compounds contain a carbonyl group OH Carbonyl group Carboxylic acid 15

Many classes of organic compounds contain a carbonyl group Ester 15

Many classes of organic compounds contain a carbonyl group NH2 Carbonyl group Amide 15

Introduction to Alkanes: Methane, CH4 General formula for an alkane CnH2n+2 Introduction to Alkanes: Methane, CH4 Ethane, C2H6 Propane, C3H8 21

No isomers possible for C1, C2, C3 hydrocarbons The simplest alkanes Methane (CH4) CH4 Ethane (C2H6) CH3CH3 Propane (C3H8) CH3CH2CH3 bp -160°C bp -89°C bp -42°C No isomers possible for C1, C2, C3 hydrocarbons 22

Isomeric Alkanes: The Butanes C4H10 General formula for any butane 21

C4H10 n-Butane Isobutane CH3CH2CH2CH3 (CH3)3CH bp -0.4°C bp -10.2°C 23

Pentane (C5H12) and Beyond Higher n-Alkanes Pentane (C5H12) and Beyond CnH2n+2 n > 4 21

CnH2n+2 n > 4 CH3CH2CH2CH2CH3 n-Pentane CH3CH2CH2CH2CH2CH3 n-Hexane CH3CH2CH2CH2CH2CH2CH3 n-Heptane 24

The C5H12 Isomers 21

C5H12 CH3CH2CH2CH2CH3 (CH3)2CHCH2CH3 n-Pentane Isopentane (CH3)4C Neopentane 25

How many isomers? The number of isomeric alkanes increases as the number of carbons increase. There is no simple way to predict how many isomers there are for a particular molecular formula. 26

Table 2.3 Number of Constitutionally Isomeric Alkanes CH4 1 C2H6 1 C3H8 1 C4H10 2 C5H12 3 C6H14 5 C7H16 9 27

Table 2.3 Number of Constitutionally Isomeric Alkanes CH4 1 C8H18 18 C2H6 1 C9H20 35 C3H8 1 C10H22 75 C4H10 2 C15H32 4,347 C5H12 3 C20H42 366,319 C6H14 5 C40H82 62,491,178,805,831 C7H16 9 27

How many isomers with the composition C6H6 Isomers How many isomers with the composition C6H6 can you draw?

C6H6 Isomers: How many isomers with the composition C6H6 can you draw?

Structure and Bonding in Alkenes 11

Structure of Ethylene planar bond angles: H-C-H = 117° H-C-C = 121° bond distances: C—H = 110 pm C=C = 134 pm planar 12

Each carbon is sp2 hybridized Bonding in Ethylene s s s s s Framework of s bonds Each carbon is sp2 hybridized

Each carbon has a half-filled p orbital Bonding in Ethylene Each carbon has a half-filled p orbital

Side-by-side overlap of half-filled p orbitals gives a p bond Bonding in Ethylene Side-by-side overlap of half-filled p orbitals gives a p bond

Isomerism in Alkenes 14

Isomers are different compounds that have the same molecular formula (composition). 2

Constitutional isomers Stereoisomers 2

Constitutional isomers Stereoisomers same connectivity; different arrangement of atoms in space different connectivity 2

Constitutional isomers Stereoisomers consider the isomeric alkenes of molecular formula C4H8 2

C H CH2CH3 C H H3C 1-Butene 2-Methylpropene H CH3 C H3C H3C C CH3 H cis-2-Butene trans-2-Butene 16

Constitutional isomers H CH2CH3 C H H3C 1-Butene 2-Methylpropene H CH3 C H3C Constitutional isomers cis-2-Butene 16

Constitutional isomers H CH2CH3 C H H3C 1-Butene 2-Methylpropene H3C C CH3 H Constitutional isomers trans-2-Butene 16

Stereoisomers H CH3 C H3C H3C C CH3 H cis-2-Butene trans-2-Butene 16

Molecular Chirality: Enantiomers 2

A molecule is achiral if its two mirror image forms are superposable. Chirality A molecule is chiral if its two mirror image forms are not superposable upon one another. A molecule is achiral if its two mirror image forms are superposable. 3

Cl Br H F It cannot be superposed point for point on its mirror image. Bromochlorofluoromethane is chiral Cl It cannot be superposed point for point on its mirror image. Br H F 4

Bromochlorofluoromethane is chiral Cl Cl Br Br H H F F To show nonsuperposability, rotate this model 180° around a vertical axis. 4

Bromochlorofluoromethane is chiral Cl Br Br Cl H H F F 4

Another look 6

nonsuperposable mirror images are called enantiomers and are enantiomers with respect to each other 7

Isomers constitutional isomers stereoisomers 8

Isomers constitutional isomers stereoisomers enantiomers (optical) geometric isomers (cis/trans) 8

Chlorodifluoromethane is achiral 9

Chlorodifluoromethane is achiral The two structures are mirror images, but are not enantiomers, because they can be superposed on each other. 9

Symmetry in Achiral Structures 19

Symmetry tests for achiral structures Any molecule with a plane of symmetry must be achiral. 18

Plane of symmetry A plane of symmetry bisects a molecule into two mirror image halves. Chlorodifluoromethane has a plane of symmetry. 21

Plane of symmetry A plane of symmetry bisects a molecule into two mirror image halves. Chlorodifluoromethane has a plane of symmetry. 21

Plane of symmetry A plane of symmetry bisects a molecule into two mirror image halves. 1-Bromo-1-chloro-2-fluoroethene has a plane of symmetry. 21

Plane of symmetry A plane of symmetry bisects a molecule into two mirror image halves. 1-Bromo-1-chloro-2-fluoroethene has a plane of symmetry. 21

Physical Properties of Alkanes and Cycloalkanes 4

increase with increasing number of carbons Boiling Points increase with increasing number of carbons more atoms, more electrons, more opportunities for induced dipole-induced dipole forces decrease with chain branching branched molecules are more compact with smaller surface area—fewer points of contact with other molecules 8

Boiling Points Heptane bp 98°C Octane bp 125°C Nonane bp 150°C increase with increasing number of carbons more atoms, more electrons, more opportunities for induced dipole-induced dipole forces Heptane bp 98°C Octane bp 125°C Nonane bp 150°C 8

2,2,3,3-Tetramethylbutane: bp 107°C Boiling Points decrease with chain branching branched molecules are more compact with smaller surface area—fewer points of contact with other molecules Octane: bp 125°C 2-Methylheptane: bp 118°C 2,2,3,3-Tetramethylbutane: bp 107°C 8

Boiling Points of Alkanes governed by strength of intermolecular attractive forces alkanes are nonpolar, so dipole-dipole and dipole-induced dipole forces are absent only forces of intermolecular attraction are induced dipole-induced dipole forces 6

Induced dipole-Induced dipole attractive forces + – + – two nonpolar molecules center of positive charge and center of negative charge coincide in each 5

Induced dipole-Induced dipole attractive forces + – + – movement of electrons creates an instantaneous dipole in one molecule (left) 5

Induced dipole-Induced dipole attractive forces – + + – temporary dipole in one molecule (left) induces a complementary dipole in other molecule (right) 5

Induced dipole-Induced dipole attractive forces – – + + temporary dipole in one molecule (left) induces a complementary dipole in other molecule (right) 5

Induced dipole-Induced dipole attractive forces – – + + the result is a small attractive force between the two molecules 5

Induced dipole-Induced dipole attractive forces – – + + the result is a small attractive force between the two molecules 5

Lots of intermolecular Straight chain hydrocarbon Branched hydrocarbon Fewer intermolecular contacts Lots of intermolecular contacts