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

HydrocarbonsHydrocarbons AromaticAromaticAliphaticAliphatic

HydrocarbonsHydrocarbons AromaticAromaticAliphaticAliphatic AlkanesAlkanes AlkynesAlkynes AlkenesAlkenes

HydrocarbonsHydrocarbons AliphaticAliphatic AlkanesAlkanes Alkanes are hydrocarbons in which all of the bonds are single bonds. C C H H H HHH

HydrocarbonsHydrocarbons AliphaticAliphatic AlkenesAlkenes Alkenes are hydrocarbons that contain at least one carbon-carbon double bond. C C H H HH

HydrocarbonsHydrocarbons AliphaticAliphatic AlkynesAlkynes Alkynes are hydrocarbons that contain a carbon- carbon triple bond. HCCH

HydrocarbonsHydrocarbons AromaticAromatic The most common aromatic hydrocarbons are those that contain a benzene ring. H H H HHH

Reactive Sites in Hydrocarbons The Functional Group Concept

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

AlkanesAlkanes 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 R—H R—X

AlkanesAlkanes functional group is a hydrogen the reaction that takes place is substitution one of the hydrogens is substituted by some other atom or group R—H R—X + Cl 2 C C H H H HHH + HCl C C H Cl H HHH

Functional Groups in Hydrocarbons alkanesRH alkenes RH, double bond alkynes RH, triple bond aromaticsArH, double bond

Some Key Functional Groups

Families of organic compounds and their functional groups AlcoholsROH Alkyl halidesRX (X = F, Cl, Br, I) Aminesprimary amine: RNH 2 secondary amine: R 2 NH secondary amine: R 2 NH tertiary amine: R 3 N tertiary amine: R 3 N EthersROR

Many classes of organic compounds contain a carbonyl group O C Carbonyl group O C Acyl group R

Many classes of organic compounds contain a carbonyl group O C Carbonyl group O C Aldehyde R H

Many classes of organic compounds contain a carbonyl group O C Carbonyl group O C Ketone R R'

Many classes of organic compounds contain a carbonyl group O C Carbonyl group O C Carboxylic acid R OH Not a ketone-alcohol!

Many classes of organic compounds contain a carbonyl group O C Carbonyl group O C Ester R OR' Not a ketone-ether!

Many classes of organic compounds contain a carbonyl group O C Carbonyl group O C Amide R NH 2 Note a ketone-amine!

Introduction to Alkanes: Methane, CH 4 Ethane, C 2 H 6 Ethane, C 2 H 6 Propane, C 3 H 8 C n H 2n+2 General formula for an alkane Alkanes

The simplest alkanes Methane (CH 4 ) CH 4 Ethane (C 2 H 6 )CH 3 CH 3 Propane (C 3 H 8 )CH 3 CH 2 CH 3 bp -160°C bp -89°C bp -42°C No isomers possible for C1, C2, C 3 hydrocarbons

Isomeric Alkanes: The Butanes C 4 H 10 General formula for any butane Isomers: same composition, different structures at the constitutional or stereochemical levels

n-Butane (bp -0.4°C) Isobutane ( bp -10.2°C ) CH 3 CH 2 CH 2 CH 3 (CH 3 ) 3 CH C 4 H 10

Higher n-Alkanes Pentane (C 5 H 12 ) and Beyond C n H 2n+2 n > 4

CH 3 CH 2 CH 2 CH 2 CH 2 CH 3 n-Pentane n-Hexane CH 3 CH 2 CH 2 CH 2 CH 3 CH 3 CH 2 CH 2 CH 2 CH 2 CH 2 CH 3 n-Heptane C n H 2n+2 n > 4

The C 5 H 12 Isomers

n-Pentane CH 3 CH 2 CH 2 CH 2 CH 3 Isopentane (CH 3 ) 2 CHCH 2 CH 3 Neopentane (CH 3 ) 4 C C 5 H 12

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. How many isomers?

Table 2.3 Number of Constitutionally Isomeric Alkanes CH 4 1 C 2 H 6 1 C 3 H 8 1 C 4 H 10 2 C 5 H 12 3 C 6 H 14 5 C 7 H 16 9

Table 2.3 Number of Constitutionally Isomeric Alkanes CH 4 1 C 8 H C 2 H 6 1 C 9 H C 3 H 8 1 C 10 H C 4 H 10 2 C 15 H 32 4,347 C 5 H 12 3 C 20 H ,319 C 6 H 14 5 C 40 H 82 62,491,178,805,831 C 7 H 16 9 (~6 x isomers!)

C 6 H 6 Isomers How many isomers with the composition C 6 H 6 can you draw?

C 6 H 6 Isomers: How many isomers with the composition C 6 H 6 can you draw?

Structure and Bonding in Alkenes

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

     Bonding in Ethylene Framework of  bonds Each carbon is sp 2 hybridized

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

Bonding in Ethylene Side-by-side overlap of half-filled p orbitals gives a  bond which makes it very difficult to rotate about the C=C bond

Isomerism in Alkenes

IsomersIsomers Isomers are different compounds that have the same composition (numbers and kinds. of atoms). Since the compounds are different, they must have different structures in the way the atoms are connected or arranged in space

IsomersIsomers StereoisomersStereoisomers Constitutional isomers

IsomersIsomers StereoisomersStereoisomers different connectivity same connectivity; different arrangement of atoms in space

IsomersIsomers StereoisomersStereoisomers Constitutional isomers consider the isomeric alkenes of molecular formula C 4 H 8

2-Methylpropene 1-Butene cis-2-Butene trans-2-Butene C CHH H CH 2 CH 3 H3CH3CH3CH3C C C CH 3 HH H C C H3CH3CH3CH3CH C C H H H3CH3CH3CH3C H3CH3CH3CH3C

2-Methylpropene 1-Butene cis-2-Butene C CHH H CH 2 CH 3 H CH 3 C C H3CH3CH3CH3CH C C H H H3CH3CH3CH3C H3CH3CH3CH3C Constitutional isomers

cis-2-Butene trans-2-Butene H3CH3CH3CH3C C C CH 3 HH H C C H3CH3CH3CH3CH Stereoisomers Same connections, different atomic positions in space

Molecular Chirality: Enantiomers

stereoisomers constitutionalisomers Isomers

stereoisomers constitutionalisomers geometric isomers (cis/trans)enantiomers(optical) Isomers Chiral structures

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. ChiralityChirality

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

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

Br Cl H F H Cl Br F

Another look

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

Chlorodifluoromethane is achiral

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

Symmetry in Achiral Structures

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

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

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