the importance of organic chemistry

The importance ofThe importance oforganic chemistryorganic chemistry

Many areas rely on organic chemistry, including:

• Biology• Petroleum• Polymers• Genetic Engineering• Agriculture• Pharmacology• Consumer Products

Importance of carbonImportance of carbon•Basis for all life.

•Form stable covalent bonds to other carbon atoms - catenation.catenation.

•Can form single, double and triple bonds.

•Long carbon chains can be produced.

•Will bond with many other elements.

•A HUGEHUGE number of compounds is possible.

CatenationCatenationThe formation of chains of atoms of the same element.

This key feature of carbon permits a vast number of compounds to exist.

One simple class of compound is the alkane which has only C, H and single bonds.

methane ethane propane butane

Hydrides of carbonHydrides of carbon

H C

H

H

H

H C

H

C

H

H

H

H

H C

H

C

H

C

H

H

H

H

H H C

H

C

H

C

H

H

H

H

C H

H

H

Formulas and modelsFormulas and models

Organic molecules can have very complex structures.

A number of formats are used to represent organic compounds.

Each has its own advantages but the goal is the same, to accurately describe the structure of a compound.

Lets look at some different representations.

FormulaFormulaCondensed structural formulaCondensed structural formula

•Shorthand way of writing formula.

•Lists all atoms in order and tells how they are bound together.

Example. Example. PropanePropane

CH3CH2CH3

This is a convenient format for describing a molecule using text.

Structural (Constitutional) isomersStructural (Constitutional) isomersCompounds with the same number and type

of atoms but with different arrangements.

Molecular FormulaMolecular Formula CC55HH1212

Condensed structural formulas.Condensed structural formulas.

CH3CH2CH2CH2CH3 pentane

CH3CH(CH3)CH2CH32-methylbutane

(CH3)4C 2,2-dimethylpropane

All are structural isomers of C5H12.

Line formulaLine formula• Similar to structural formula.• Each line represents a bond.• Carbons are assumed to be present at the end of

each line segment.• Hydrogen is not shown when bound to carbon.

NOH H

H2C

CH2

CH2

CH2

H2C

H2C

H2C

CH2

CH2

H2C

H2C

H2C

H2C

CH2

CH2

N

H2C

H2C

H2C

CH2

CH2

H2C

H2C

H2C

OH HH2C

CH3

ModelsModelsThree dimensional representations

Ball and StickBall and Stick

Space FillingSpace Filling

Both are models of propane.

AlkanesAlkanesSimplest members of the hydrocarbon

family.

•contain only hydrogen and carbon•only have single bonds

All members have the general formula of

CnH2n+2

Twice as many hydrogenas carbon + 2Twice as many hydrogenas carbon + 2

AlkanesAlkanes

First four members of the alkanes

Name # of C Condensed formulaMethane 1 CH4

Ethane 2 CH3CH3

Propane 3 CH3CH2CH3

Butane 4 CH3CH2CH2CH3

Called a homologous serieshomologous series“Members differ by number of CH2 groups”

AlkanesAlkanes

Physical PropertiesPhysical Properties

Nonpolar molecules

Not soluble in water

Low densityLow density

Low melting pointLow melting point

Low boiling pointLow boiling point

These go upas the number

of carbonsincreases.

These go upas the number

of carbonsincreases.

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12.7 Properties of Alkanes12.7 Properties of Alkanes

Odorless or mild odor; colorless; tasteless; nontoxic

Flammable; otherwise not very reactive

The first four alkanes are gases at room temperature and pressure, alkanes with 5–15 carbon atoms are liquids; those with 16 or more carbon atoms are generally low-melting, waxy solids.

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The boiling and melting points for the straight-chain alkanes increase with molecular size.

AlkanesAlkanes

Name bp, oC mp, oC Density at 20 oC

Methane -161.7 -182.6 0.000 667Ethane - 88.6 -182.8 0.001 25Propane - 42.2 -187.1 0.001 83Butane -0.5 -135.0 0.002 42Pentane 36.1 -129.7 0.626Hexane 68.7 - 94.0 0.659Heptane 98.4 - 90.5 0.684Octane 125.6 - 56.8 0.703 Nonane 150.7 -53.7 0.718Decane 174.0 -29.7 0.730

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Sources of alkanesSources of alkanes

Alkanes can be obtained by refining orhydrogenation of:

petroleumpetroleumshale oilshale oilcoalcoal

Low molecular mass alkanes can be obtained directly from natural gas.

Reactions of alkanesReactions of alkanes

CombustionCombustion

CH4(g) + 2O2(g) CO2(g) + 2H2O(g)

Many alkanes are used this way - as fuels

MethaneMethane - natural gas

PropanePropane - used in gas grills

ButaneButane - lighters

GasolineGasoline - mixture of many hydrocarbons, not all alkanes

Reactions of alkanesReactions of alkanes

HalogenationHalogenationA reaction where a halogen replaces one or

more hydrogens.

CH4(g) + Cl2(g) CH3Cl(g) + HCl(g)

Used to prepare many solvents•dichloromethane - paint stripper•chloroform - once used as anesthesia•1,2-dichloroethane - dry cleaning fluid

heat or light

Organic nomenclatureOrganic nomenclature

Organic molecules can be very complex.

Naming system must be able to tell

•Number of carbons in the longest chainNumber of carbons in the longest chain

•The location of any branchesThe location of any branches

•Which functional groups are present Which functional groups are present and where they are located.and where they are located.

The IUPACIUPAC Nomenclature System provides a uniform set of rules that we can follow.

Base namesBase namesPrefix CarbonsMeth- 1Eth- 2Prop- 3But- 4

Pent- 5Hex- 6Hept- 7Oct- 8Non- 9Dec- 10

I see muchmemorization in

your future!

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Naming AlkanesNaming AlkanesIUPAC RulesIUPAC Rules

Acylcic, saturated hydrocarbons end in “-ANE”Named by the number of carbons in the “chain”The Root is the longest carbon chainSubstituents or alkyl groups named by the

number of carbonsSubstituents are identified by the number of the

carbon and how many of that type of group. (mono = 1, di = 2 , tri = 3, tetra = 4 etc.)

Two or more different substituents are listed alphabetically ethyl before methyl

Names are one word. Numbers are separated by commas and names are separated by hyphens. There are no spaces between the substituent and the root names

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12.6 Naming Alkanes12.6 Naming Alkanes

The system of naming now used is one devised by the International Union of Pure and Applied Chemistry, IUPAC.

In the IUPAC system for organic compounds, a chemical name has three parts: prefix, parent, and suffix.

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Drawing Organic StructuresDrawing Organic Structures

Condensed structure: A shorthand way of drawing structures in which C-C and C-H bonds are understood rather than shown.

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Branched-chain alkanesSTEP 1: Name the main chain. Find the

longest continuous chain of carbons, and name the chain according to the number of carbon atoms it contains. The longest chain may not be

immediately obvious because it is not always written on one line; you may have to “turn corners” to find it.

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STEP 2: Number the carbon atoms in the main chain. Begin at the end nearer the first branch point:

► STEP 3: Identify the branching substituents, and number each according to its point of attachment to the main chain:

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STEP 4:Write the name as a single word, using hyphens to separate the numbers from the different prefixes and commas to separate numbers if necessary. If two or more different substituent groups are present, cite them in alphabetical order.

► If there are two substituents on the same carbon, assign the same number to both. There must always be as many numbers in the name as there are substituents.

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If two or more identical substituents are present, use one of the prefixes di-, tri-, tetra-, and so forth, but do not use these prefixes for alphabetizing purposes.

ExamplesExamples

C-C-C-C-C-CC-C-C-C-C || |C-CC-C C

C-C-C-C-C-C-C | |

C-C C


| C

3,5-dimethylheptane

ExamplesExamples

C-C-C-C-C-C-CC-C-C-C-C-C-C | |

C-C C

C-C-CC-C-C-C C-C-CC-C || | | C-C-C-C-C-CC-C-C-C-C-C

| C

3,5-dimethyl heptane

2,3,3,7,8-pentamethyldecane

C-C-C-C-C-CC-C-C-C-C || |C-C C-C C

3-ethyl-5-methylheptane

Another exampleAnother example

Name the following.

(CH3)2CHCH2CH2CH(CH3)2

This is a condensed structural formula.

First convert it to a carbon skeleton, leavingout the hydrogens.


(CH3)2CHCH2CH2CH(CH3)2

C C | |C - C - C - C - C - C

Now name it!


C C | |C - C - C - C - C - CC - C - C - C - C - C

1. Longest chain is 6 - hexane

2. Two methyl groups - dimethyl

3. Use 2,5-dimethylhexane

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The situation is more complex for larger alkanes. There are two different three carbon alkyl groups,

there are four different four carbon alkyl groups.

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Substituents to a Carbon ChainSubstituents to a Carbon Chain

Alkyl ChainsNamed by number of carbonsStraight chainsBranched chains

iPrsBuiButBu

HalidesBranch nameHalohydrocarbons

Naming alkyl halidesNaming alkyl halides

1. Follow the same system as with alkanes.

2. Give the name and carbon number for the halide just like a side branch.

C - C - F C - C - C C-C-C-C-C | |

Cl C-Br1-fluorofluoroethane

2-chlorochloropropane

1-bromobromo-2-ethylbutane

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PracticePractice

2,3 dimethylpentane3-ethyl-4-methlylheptane4-propyl-2,2,3,3-tetramethyloctane4-isopropyloctane

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Drawing and Naming CycloalkanesDrawing and Naming Cycloalkanes

Ring structures are possible and very important in organic chemistry.

A more streamlined way of drawing structures is often used in which cycloalkanes are represented simply by polygons.

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In line structures, a C is located at every intersection, and the number of H atoms necessary to give each C four covalent bonds is understood. Methylcyclohexane, for example, looks like this in a line structure:

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STEP 1: Use the cycloalkane name as the parent. named as alkyl-substituted cycloalkanes

rather than as cycloalkyl-substituted alkanes.

If there is only one substituent on the ringit is not necessary to assign a

number because all ring positions are identical.

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STEP 2: Identify and number the substituents.

Start numbering at the group that has alphabetical priority,

Proceed around the ring in the direction that gives the second substituent the lower possible number.

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1,2,4,4,5-pentachlorocylooctane.1,2,4,4,5-pentachlorocylooctane.DrawDraw

Start by drawing an octagon. Number the carbons and draw in

substituents

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Cyclic Alkane PropertiesCyclic Alkane PropertiesCyclic compounds have ring strain.They are more eclipsing than linear molecules

and can’t rotate to relieve strain.Also to convert the tetrahedral bond angles to

the angles necessary for a ring causes bond-angel strain.

Cyclopropane is planer and unstable.Cyclobutane is not planer but “puckered”Cyclopentane has the “envelope” and “half-

chair” shapes rather than being planer.Cyclohexane is not planar as well, has “chair”

and “boat” formations.All to relieve stress and lower potential energy.

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Conformations of CylcohexaneConformations of Cylcohexane

Chair Conformation

Axial groups are close in space, so the smallest substituent will be in the axial postion

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The Chair Conformation Can FlipThe Chair Conformation Can Flip

All the axial positions become equatorial after a flip

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↔Flip

Which confirmation is favored?Can you draw a Newman projection of carbon 1 and 2 for each conformation?

Methyl CylohexaneMethyl Cylohexane

Multiple bondsMultiple bonds

Another key feature of carbon is its ability to form double and triple bonds.

This can be between two carbonsalkenes (C=C) and alkynes (C C)

It can also be between carbon and another element.

C=OC=N-C N

Ethane, C-C single bondEthane, C-C single bond

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RotationsRotationsSince the central atom can rotate, then the

hydrogens can line up (eclipsed) or be staggered

There is a potential energy difference between the two positions.

The change in energy is called torsional energy or rotational energy

Due to this, the molecule is more likely to be staggered rather than eclipsed.

The bigger the carbon chain and groups that would be eclipsed, the harder the rotation is.

Called steric hindrance.Gauche and anti – 4 carbons or more.

Ethene or ethylene, C=C double bondEthene or ethylene, C=C double bond

Ethyne or acetylene, C C triple Ethyne or acetylene, C C triple bondbond

Naming alkenes and alkynesNaming alkenes and alkynes1. All multiple bonds must be included as

part of the main chain, even if it is not physically the longest chain.

2. Multiple bonds take priority over substituted groups in determining the lowest number.

3. Follow the same system as with alkanes.

C C - F C-C-C-C=C |

C-Brfluorofluoroethyne4-bromobromo-3-ethyl-1-butene

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Alkanes and Saturated HydrocarbonsAlkanes and Saturated HydrocarbonsSaturated fat and unsaturated fat

Unsaturated means there is a C=CPolyunsaturated means there are 2 or

more C=C

How can you tell if a hydrocarbon is saturated?

Why are they healthier to eat?

What phase to they tend to be?

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Alkenes and AlkynesAlkenes and AlkynesSimple alkenes are made in vast quantities

in the petroleum industry by thermal “cracking” of the alkanes in petroleum.

Most of the organic chemicals used in making drugs, explosives, paints, plastics, and pesticides are synthesized by routes that begin with alkenes.

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Classification of Unsaturated Classification of Unsaturated HydrocarbonsHydrocarbons

Alkene – has a carbon carbon double bondDiene- has 2 C=C bonds

Conjugated, C=C-C=C, (interacting ∏ bonds)

Cummulated, C=C=C

Nonconjugated diene, C=C-Cn-C=C, (noninteracting ∏’s)

Conjugated is much more stable than nonconjugated.

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Which carbons are conjugated?Which carbons are conjugated?

http://www.3dchem.com/3dmolecule.asp?ID=103



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Nomenclature of Alkenes and AlkynesNomenclature of Alkenes and AlkynesEnding for C=C is -ene, Ending for C=C is –yne

Compounds with both are –enynes.Select longest chain with the unsaturation

Number the chain so unsaturation has the lowest number1.The name starts with the “smallest

number”2.If there are two double bonds, use the

order with the lowest number 3.If there are a double and a triple bond, the

order with the double bond being lowest has priority

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Naming Alkenes and AlkynesNaming Alkenes and AlkynesIn the IUPAC system, alkenes and alkynes are

named by a series of rules similar to those used for alkanes. The parent names indicating the number of carbon atoms in the main chain are the same as those for alkanes, with the -ene suffix used in place of -ane for alkenes and the -yne suffix used for alkynes.

STEP 1: Name the parent compound. Find the longest chain containing the double or triple bond, and name the parent compound by adding the suffix -ene or -yne to the name for the main chain.

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Name the parent compound. Find the longest chain containing the double or triple bond, and name the parent compound by adding the suffix -ene or -yne to the name for the main chain.

The number of multiple bonds uses a numerical prefix diene = 2 double bondstriene = 3 double bonds and so on…tetra, penta, hexa,

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Number the carbon atoms in the main chain, beginning at the end nearer the multiple bond. If the multiple bond is an equal distance from both ends, begin numbering at the end nearer the first branch point.

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Write the full name. Assign numbers to the branching substituents,

and list the substituents alphabetically. Use commas to separate numbers and

hyphens to separate words from numbers. Indicate the position of the multiple bond in the

chain by giving the number of the first multiple-bonded carbon. If more than one double bond is present, identify the position of each and use the appropriate name ending for example, 1,3-butadiene and 1,3,6-

heptatrieneFor historical reasons, there are a few alkenes

and alkynes whose names do not conform strictly to the rules.

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Alkenes and alkynes differ from alkanes in shape because of their multiple bonds.

Methane is tetrahedral, ethylene is flat and acetylene is linear, as predicted by the VSEPR model.

Unlike the situation in alkanes, where free rotation around the single bond occurs, there is no rotation around the double bonds..

StereoisomersStereoisomers

Structural isomers are not the only types that can exist.

Stereoisomers haveStereoisomers have•the same order and types of bonds.

•different spatial arrangements.•different properties.

Many biologically important compounds, like sugars, exist as stereoisomers. Your body can tell the difference.

StereoisomersStereoisomers

Two kinds of stereoisomers exist.

Cis-trans (Geometric) isomersCis-trans (Geometric) isomersWhen a double bond exists between carbons or carbons form a ring, a molecule can exist in two geometric forms.

Optical isomersOptical isomersWhen molecules can exist as mirror-image isomers or enantiomers.

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Cis and Trans IsomerismCis and Trans IsomerismConfigurational stereoisomersConfigurational stereoisomers

Cis –same side

Trans – opposite sides

They are different compounds

No free rotation

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Cis–trans isomerism whenever each double-bond carbon is

bonded to two different substituent groups.

If one of the double-bond carbons is attached to two identical groups, cis–trans isomerism is not possible.

Retinal and sightRetinal and sight

Light causes achange from cis-to trans-. This ishow we see.

Several enzymesare requiredto convert trans-retinalBack to thecis-form.

cis-retinal

trans-retinal

O

light several steps

O

3-D models of retinal3-D models of retinal

cis-

trans-

EnantiomersEnantiomersPairs of stereoisomersPairs of stereoisomers

Sometimes designated by D- or L- at the start of the name.

They are mirror images that can’t be superimposed.

If you don’t believe it,give it a try!

EnantiomersEnantiomers

LL- and - and DD- glyceraldehyde- glyceraldehyde

CHO

HO H

C

CH OH2

CH OH2

H

CHO

HO

CHO

H

C

CH OH2

OH

CH OH2

H

CHO

OH

EnantiomersEnantiomers

Stereocenter.Stereocenter.Chiral center or asymmetric carbon Chiral center or asymmetric carbon - four different things are attached to it.

Cl |

I - C - F |

Br

A molecule that has one stereocenter exists as a pair of enantiomers.

Chiral center

ExamplesExamples

Is the ‘red’ carbon a stereocenter?

H

HOCC=O

CC-OHH

H3C-

H

CC-OH

CH2CH3

H3C-

H

H | C=O | H-CC-OH |

CH2OH

CC=CCl

Br

I

F

H2N-C-C-CC-C-C-SH

H H H

HCl Cl

Classifying organic compoundsClassifying organic compoundsFunctional Groups take priority!!!Functional groupFunctional group - Specific combination of atoms

that gives a known type of behavior.Alcohols R-OHOH -ol-olAcids R-COOHCOOH -oic Acid-oic AcidAmines R-NHNH22 -amine-amineKetones R(C=OC=O)R’ -oneAldehydes R-CHOCHO -al-alAmidesAmides R-R-CONHCONH22 -amide-amide

EthersEthers R-R-OO-R-R’’ etheretherEstersEsters R-R-OOOO-R’-R’ -oate-oateThiolsThiols R-R-SHSH -thiol-thiolNitrilesNitriles R-R-CNCN -nitrile-nitrile

Alcohol exampleAlcohol exampleC - C - C - C - O - H

The IUPAC system deals with functional groups two different ways.

Base contains 4 carbon- alkane name is butane- remove -e-e and add -ol -ol

alcohol name - butanol

OH is on the first carbon so…..1-butanol1-butanol

alternate name: alternate name: 1-hydroxylbutane1-hydroxylbutane

Example: CH3CH2COOH

1. Longest chain containing carbonyl is 3,

propanepropane

2. The -e ending is replaced with -oic acid,

propanoic acidpropanoic acid

Acid exampleAcid example

Physical propertiesPhysical properties

Optical activityOptical activityability to rotate plane-polarized light.

dextrorotatorydextrorotatory - rotate clockwise- use + symbol- usually D isomers

levorotatorylevorotatory - rotate counterclockwise- use - symbol- usually L isomers

Plane polarized lightPlane polarized light

Light is passed through a polarized filter.A solution of an optical isomer will rotate the light one direction.

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Organic ReactionsOrganic ReactionsPyrolysisSubstitution

-halogenation – with a halogen-SN2 – with a nucleophile-SN1 or hydrolysis (solvolysis) – substitution by solvent

E1 - Elimination – removes halogen and makes alkeneE2 – Elimination – same as E1 but different mechanismHydrogenation – double bond eliminated by hydrogenHydration – double bond is eliminated and makes an

alcohol.Dehydration – water is released.Electrophilic addition – double bond is broken by a

strong acid.Polymerization – taking alkenes and linking them into

(essentially) unending chains.

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REDOX and organicsREDOX and organics

Oxidation is defined as any process that adds electronegative atoms or removes hydrogen.

Reduction is any process that adds hydrogen and removes electronegative elements.

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Homo and heterolytic cleavageHomo and heterolytic cleavageWhen a bond is broken, each fragment gets

one of the electrons from the bond and is left with an extra unpaired electron

This is called homolysis or homolytic cleavage.

The result is two free radicalsUsually free radicals are intermediates and

are high energy.A-B → AA.. + B + B..

If a bond is broken and both electrons go to one fragment, then they both become ions

This is called heterolytic cleavage.A-B → AA++ + :B + :B--

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PyrolysisPyrolysisWhen alkanes are exposed to high

temperatures, C-H and C-C bonds begin to break leaving two radicals.

The radicals can combine to form smaller chains.

Process is called cracking.Heat can also cause hydrogen to be lost from

the radical leaving an alkeneCalled hydrogen abstraction.

CH3CH2. + CH3CH2CH2

.→ CH3CH3 + CH3CH=CH2

Zeolytes (catalysts like sodium aluminosilicates) help specialize what products will be made.

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HyperconjugationHyperconjugationWhen the electron is removed from the

molecule, an sp3 orbital is left half empty.

The electron in the orbital delocalizes into a p orbital leaving the other bonds in a planar formation.

Resonance and hyperconjugation are forms of delocalization of electrons.

Resonance is of a π bond overlap of p-orbitalsHyperconjugation is delocalization with σ bonds.

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Substitution ReactionSubstitution ReactionA general reaction type in which an atom or group of atoms in a molecule is replaced by another atom or group of atoms.

Halogenation reactions are one type:

86

22 - 87

HalogenationHalogenationActivity series determines which halogen is

most likely to react and substituteFluorine is exothermic, the rest are increasingly

endothermic.UV light breaks the halogen bond enabling the

reaction.Secondary carbons are more likely to

substitute than primary.Tertiary are more likely than secondary.

SSNN2 mechanism2 mechanismReaction mechanisms provide a powerful way

to organize the vast amount of information about organic reactions.

SSNN2 mechanism2 mechanism• One very important reaction mechanism.

• The symbol (SN2) stands for substitution nucleophilic bimolecular.

NucleophileNucleophile“Nucleus loving.” A species that is attracted by a positive charge.

OH-, I-, NH3, CH3O-, NC-

SSNN2 mechanism2 mechanismExampleExample

HO- + CH3Br (aq) CH3OH (aq) + Br-

For this reaction:

• HO- is the nucleophilenucleophile. Increases with increasing negative charge, decreases to right on periodic table

• CH3Br is the substratesubstrate - a species that undergoes reaction.

• Br- is the leaving groupleaving group. Because it is replaced by HO-. Weak bases are good leaving groups.

SSNN2 mechanism2 mechanism

The mechanism takes place in a single step. This is supported by the observed rate law.

Rate = k [HO-][CH3Br]

SN2 reactions also take place with inversion of configuration.

CH3 ClCH3

OH

+ HO- + Cl-


HO-

+ Br-

Br

H

C

HH

HO

H

C

H H

H

H H

BrHO+ -

- +

To account for the inversion,the nucleophile must approachfrom the back of the carbon

The nucleophile acts as a Lewisbase and the substrate as aLewis acid.

To account for the inversion,the nucleophile must approachfrom the back of the carbon

The nucleophile acts as a Lewisbase and the substrate as aLewis acid.


Predicting whether an SN2 reaction will occur is possible.

The SN2 reaction

Nuc:- + RX RNuc + X-

is similar to a Bronsted-Lowry acid base reaction

B:- + HX HB + X-


To predict whether a SN2 reaction will occur, you must consider the relative base strength of the nucleophile and the leaving group.

If the nucleophile is a stronger base, the reaction will occur.Relative base strengthRelative base strength

OH- > Cl- > Br- > I-

Second order based on concentration of the base and the halide.

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Hydrolysis (SHydrolysis (SNN1)1)

Haloalkane reacts with water solvent.Halogen ionizes away from a carbon leaving

a carbocation.Tertiary carbocations are the best while

primary are the worst.Due to hyperconjugation the positive

charge is stabilized in the tertiary formation.

Polar water is attracted to carbocation.Extra hydrogen is attracted to next water

molecule to create a hydronium ion. First order based on concentration of halide.

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E1 EliminationE1 EliminationHaloalkanes react with a base or nucleophile.Alternate SN1 pathway.Instead of adding water, it kicks out another

proton (H+) and forms a double bond between carbons in its place.

Leaves you with an alkene and a halogenated acid.

Weak bases give substitutions SN1and SN2, strong bases give eliminations E1.

First order reaction: only dependent on the concentration of the halide.

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E2 - EliminationE2 - Elimination

Second order reaction due to concentration of both the halide and the base.

Base attacks a hydrogen on a carbon away from the halide.

Hydrogen leaves donating its electron pair to the carbon giving it four pairs.

Carbon makes double bond with the other carbon which causes the release of the halogen ion.

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HydrogenationHydrogenation

A carbonyl group from an aldehyde or a ketone or a double bond in an alkene is attacked by hydrogen gas or some other hydride in the presence of a catalyst.

Catalyst is usually heterogeneous (insoluble) like platinum, palladium, or nickel deposited on carbon.

Results in an alcohol when an aldehyde or ketone is involved, and an alkane when an alkene is involved.

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Hydration: The addition of water, in the presence of a strong acid catalyst, to a multiple bond to give an alcohol product.

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DehydrationDehydrationA strong acid is added to an alcohol making a

halide and water. HBr + C2H5OH → C2H5Br + H2O

A carboxylic acid and alcohol react in the presence of an acid to make an ester.

Called esterfication.

An alcohol in acid (sulfuric) make an ether and water.

An alcohol with an acid and heat will make an alkene

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Electrophilic AdditionElectrophilic Addition

The acid attacks the pi bond breaking it an leaving a carbocation.

The halogen attaches to the ion to make a halide.

Also called hydrohalogenation.Product can be determined using

Markalnikov’s rule.

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HydrohalogenationHydrohalogenation

101

Hydrochoric and hydrobromic acids are hydrohalidesHCl, HBr

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Markovnikov’s ruleMarkovnikov’s rule

In the addition of HX to an alkene, the H attaches to the carbon that already has the most H’s, and the X attaches to the carbon that has fewer H’s.

102

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Markonvnikov’s RuleMarkonvnikov’s Rule

103

Only one product is produced because of the mechanism of hydrohalogenation

22 - 104104

Reaction Mechanism

22 - 105

Use Markovnikov’s rule to predict the product for a hydration as well.

22 - 106

AlkynesAlkynes

It is important to note that all reactions that occur with alkenes will occur in alkynes.

Each step in the mechanism just has to happen twice.

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BiochemistryBiochemistryThe body uses complex catalysts to help with these organic

reactions, but the principles and products are the same.Ex. Alcohol in the body.NAD+ is called a dehydrogenase (enzyme) because it removes

two hydrogens each time.It is also the electron acceptor in the redox.

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Oxidation of Alcohols, Aldehydes, Oxidation of Alcohols, Aldehydes, Ketones and Carboxylic AcidsKetones and Carboxylic Acids

1˚ primary alchohol Aldehyde Carboxylic Acid

2˚ primary alchohol Ketone

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Alkene PolymersAlkene Polymers

A polymer is a large molecule formed by the repetitive bonding together of many smaller molecules called monomers.

PolymersPolymers

Because the monomer units in synthetic polymers are all the same (except for copolymers), an abbreviated formula can be used.

MonomerMonomer PolymerPolymerEthylene polyethylene

Vinyl chloride poly(vinyl chloride)

C C

H

H

H

H

C C

Cl

H

H

H

- CH2-CH2 - ( )n

-CH2-CH -( )n|

Cl

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PolymerizationPolymerization

Polymers are formed either by:

Chain polymerizationChain polymerizationA multi-step process involving initiation, propagation and termination. Polymer size is relatively uniform.

Stepwise polymerizationStepwise polymerizationA process where polymer size and amount increase as a function of time.

Chain polymerizationChain polymerization

Chain initiationChain initiation

• This is the first step in chain polymerization.

• An initiator is added to form a radical species which adds to a monomer.

• The resulting species is also a radical.

Rad + CH2 CHCl Rad CH2 CHCl


Chain propagationChain propagation

• The newly formed radical is then able to react with another monomer unit.

• This process will continue, resulting in an increasing longer chain.

Rad-CH2-CHCl + CH2 CHCl

Rad-CH2-CHCl -CH2-CHCl

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Chain terminationChain termination• This occurs when two radicals combine.• Initially unlikely occurrence because much

more monomer than radical is present.• As the monomer is depleted, termination

becomes much more likely.

Rad-CH2-CHCl -CH2-CHCl + Rad-CH2-CHCl -CH2-CHCl

Rad-CH2-CHCl -CH2-CHCl CHCl-CH2-CHCl-CH2-Rad

Step polymerizationStep polymerization

For step polymerization to occur, each monomer unit must have two reactive groups.

Example. Preparation of nylon.Example. Preparation of nylon.

ClC(CH2)4CCl||O

||O

H2N(CH2)6NH2

Adipoyl chloride hexamethylenediamine

ClC(CH2)4C||O

||O

-NH(CH2)6NH2 + HCl

+

Step polymerizationStep polymerization

Product still has two reactive groups.

Polymer length is a function of time.

ClC(CH2)4C||O

||O

-NH(CH2)6NH2

Polymer typesPolymer types

FibersFibersThese result when the intermolecular forces between polymer molecules are strong.

Chains can be lined up by stretching.

HO

O

HO

O

HO

O

HO

O

HO

HO

O

HO

O

HO

O

HO

O

HO


ElastomersElastomersIn these polymers, intermolecular attractions are weak.

Crosslinking the chains is one way of helping them to maintain a shape. crosslink


PlasticsPlasticsSomewhere between fibrous polymers and elastomers.

ThermoplasticThermoplasticSoften when heatedExample - polyethylene.

Thermoset plasticThermoset plasticDo not soften when heated.These are typically highly crosslinked polymers.

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Polymers in the BodyPolymers in the Body

Amino acids linking to make proteins.

DNA and RNA

In both cases the body uses enzymes to assist in the creation to ensure the function will be correct.

Skin and cell membranes are also polymers of a sort (lipids)

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Aromatic CompoundsAromatic Compounds

Compounds containing benzene-like rings.Conjugated rings.Benzene and other aromatic compounds are

much less reactive than alkenes.

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Structure of Benzene, CStructure of Benzene, C66HH66

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Benzene is relatively stableThe ring system is preserved in reactions

All C-C bonds are identical.

125


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bond is an intermediate between a C-C and C=C.

Simple aromatic hydrocarbons like benzene are nonpolar, insoluble in water, volatile, and flammable. (like alkanes)

126


22 - 127127

Naming Aromatic CompoundsNaming Aromatic Compounds

Substituted benzenes are named using -benzene as the parent.

No number is needed for monosubstituted benzenes because all the ring positions are identical.

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Phenyl and Benzyl GroupsPhenyl and Benzyl Groups

128Benzyl group

CH2

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Ortho, Meta and ParaOrtho, Meta and Para

129

Number the ring so have the smallest numbers

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Common NamesCommon Names

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Benzene

Toluene

Cumene

Styrene

Phenol

Benzaldehyde

Benzoic acid

Aniline

Benzene

Toluene

cumene

Styrene

phenol

benzaldehyde

Benzoic Acid

aniline

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H

CH=CH2

CH3

CHCH3

CH3


Benzene

Toluene

Cumene

Styrene

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OH

NH2

Phenol

Aniline

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CH=O

O-

CH2-

CO2H


Benzaldehyde

Benzoic Acid

benzyl

phenyl

Groups

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Reactions of Aromatic Reactions of Aromatic CompoundsCompounds

Unlike alkenes, which undergo addition reactions, aromatic compounds usually

undergo substitution reactions.

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ReactionsReactions

FeCl3 →

HNO3 →

Halogenation

NitrationH2SO4

Cl

NO2HONO2

Nitrobenzene

Chlorobenzene

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ReactionsReactions

R-Cl →

CH2=H2 →

Friedel-Crafts Alkylation

H2SO4

AlCl3

R

CH2CH3

OC-R

AlCl3

OR-C-Cl →

║ ║

22 - 138138

Nitration is the substitution of a nitro group for one of the ring hydrogens.

The reaction occurs when benzene reacts with nitric acid in the presence of sulfuric acid as catalyst:

22 - 139Copyright © 2010 Pearson Education, Inc.

Chapter Thirteen 139

Halogenation is the substitution of a halogen atom, usually bromine or chlorine, for one of the ring hydrogens.

The reaction occurs when benzene reacts with Br2 or Cl2 in the presence of iron as catalyst:

the importance of organic chemistry

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