chapter 19 - introduction to organic chemistry

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1 Chapter 19 Chapter 19 Introduction to Introduction to Organic Chemistry Organic Chemistry

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Intro to Organic Chemistry

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Page 1: Chapter 19 - Introduction to Organic Chemistry

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Chapter 19Chapter 19

Introduction toIntroduction toOrganic ChemistryOrganic Chemistry

Page 2: Chapter 19 - Introduction to Organic Chemistry

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19.1 The beginnings of organic chemistry19.1 The beginnings of organic chemistrylarge number of remarkably stable compoundsconsist of C, H, O and N –organic compoundsno organic compounds had been synthesized frominorganic substance before the early 19th centurythe vital-force theory –organic substances couldoriginate only from living material1828 Wöhler

HCNO + NH3 ╳ NH4+CNO-

NH2O=C urea

NH2the sources of organic compounds are carbon-containing raw materials –petroleum and naturalgas, coal, carbohydrates, fats, and oils

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19.2 The carbon atom19.2 The carbon atomC electron structure 1s22s22p4

two stable isotopes: C-12 and C-13a carbon atom usually forms four covalent bondswith tetrahedral geometry

ex. methane CH4 carbon tetrachloride CCl4H Cl.. ..

H:C:H Cl:C:Cl.. ..H Cl

one, two, or three pairs of electrons can be sharedbetween two C atoms, forming a single, double, ortriple bond . . . .

·C—C· ·C=C· ·C≡C·. .through this bonding ability, long chains of Catoms form by liking one to another

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organic molecules are classified according to theirstructural featureseach class of compounds contain a characteristicatom or group of atoms called a functional group

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19.3 Hydrocarbons19.3 Hydrocarbonshydrocarbons –compounds composed entirely of

C and H atomssaturated hydrocarbons have only C—C singlebondsunsaturated hydrocarbons contain a double ortriple bond between two C atoms, includealkene, alkyne and aromatic compounds

general classification of hydrocarbons

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19.419.4 AlkanesAlkanesalkanes paraffins saturated hydrocarbons

straight- or branched-chain hydrocarbons withonly single bonds between the C atomsallowed energies

the first member –methane CH4

each member of a series differ in formula from thenext member by a CH2 group, the series is knownas homologous seriesthe general formula for open chain alkanes isCnH2n+2

combustion reaction generates heatex. CH4 + 2 O2 CO2 + 2 H2O + 802.5 kJ

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19.5 Structural formulas and isomerism19.5 Structural formulas and isomerismalkane molecules only contain C—C and C—Hbondsalkane molecules are essentially nonpolar, and havelittle intermolecular attraction and thereforerelatively low boiling pointsthree-dimensional structures

methane CH4 ethane C2H6 propane C3H8

butane C4H10 normal butane 2-methylpropane

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normal propane bp 0.5oC mp -138.3oC2-methylpropane bp -11.7oC mp -159.5oC

isomerism –the phenomenon that two or morecompounds have the same molecular formula

the individual compounds are called isomersbutane 2 isomers pentane 3 isomershexane 5 isomers heptane 9 isomersoctane 18 isomers nonane 35 ismersdecane 75 isomers

isomers are compounds with the same molecularformula but different structural formula

ex. 19.1 write the structural formulas for threeisomers of pentane

C—C—C—C—C CH3CH2CH2CH2CH3C CH3| |

C—C—C—C CH3CHCH2CH3C CH3| |

C—C—C CH3CCH3 or C(CH3)4| |C CH3

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19.6 Naming19.6 Naming alkanesalkanesIUPAC system is generally unambiguous andinternationally accepted

common alkyl groups CnH2n+1-ane -yl

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IUPAC rules for naming alkanes

ex.

2-methylbutane 2-methylpentane

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2,3-dimethylbutane 2,2-dimethylbutane

3-methylhexane

2,3,4,6-tetramethylheptane

3-chloro-4-ethyl-2,4-dimethyloctaneex.19.2 write the formulas for(a) 3-ethylpentane1 2 3 4 5 1 2 3 4 5C—C—C—C—C CH3CH2CH2CH2CH3

|CH3

(b) 2,2,4-trimethylpentane CH31 2 3 4 5 1 2 3 4 5C—C—C—C—C CH3CCH2CHCH3

| |CH3 CH3

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ex. 19.3 name these compounds6 5 4 3 2 1

(a) CH3CH2CH2CH2CHCH3|CH3

hexane 2-methylhexane8 7 6 5 4 3

(b) CH3CH2CH2CHCH2CHCH3| |2 1CH3CH2 CH2CH3

octane 5-ethyl-3-methyloctane

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19.7 Alkenes and alkynes19.7 Alkenes and alkynesalkenes contain at least a C=C double bondalkynes contain at least a C≡C triple bondthe simplest alkene C2H4 ethene (ethylene)the simplest alkyne C2H2 ethyne (acetylene)

general formula for alkenes: CnH2ngeneral formula for alkynes: CnH2n-2

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19.8 Naming alkenes and alkynes19.8 Naming alkenes and alkynesto name an alkene (or alkyne) by the IUPAC system

ex. 4 3 2 1 4 3 2 1CH3CH2CH=CH2 CH3CH=CHCH3

1-butene 2-butene4 3 2 1 6 5 4CH3CH2C≡CH CH3CH2CH2

|3 2 11-butyne CHCH=CH2

|CH3CH2CH2

CH3 3-propyl-1-hexene1 2 3 4| 5 6CH3C ≡C—CH—CH—CH3

|CH3 4,5-dimethyl-2-hexyne

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ex. write the structural formulas for(a) 7-methyl-2-octene

8 7 6 5 4 3 2 1

CH3—CH—CH2—CH2—CH2—CH=CH—CH3|

CH3

(b) 3-hexyne6 5 4 3 2 1

CH3—CH2—C≡C—CH2—CH3

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19.9 Reactions of alkenes19.9 Reactions of alkenesalkenes are much more reactive than alkanesaddition reaction –a reaction in which two

substances join to produce one producthydrogen, halogens, hydrogen halides and watercan be added to C=C double bondex. Pt 25oC

CH2=CH2 + H2 CH3—CH31 atm

CH2=CH2 + Br—Br BrCH2—CH2Br

CH2=CH2 + HCl CH3—CH2Cl

H+

CH2=CH2 + HOH CH3CH2OH

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19.10 Aromatic hydrocarbons19.10 Aromatic hydrocarbonsbenzene and all substances with structures andchemical properties resembling benzene areclassified as aromatic compoundsbenzene C6H6

the structure

although benzene looks as highly unsaturated, itdoes not readily undergo addition reactions likea typical alkeneits typical reaction is substitution reaction:

C6H6 + Cl2Fe C6H5Cl + HCl

the modern molecular orbital structure ofbenzene

chlorobenzene

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19.11 Naming aromatic compounds19.11 Naming aromatic compoundsmonosubstituted benzenes

disubstituted benzenesortho-, meta-, para- (o-, m-, p-)

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trisubstituted benzenes

ex. 19.5 write formulas and names for allpossible isomers of

(a) chloronitrobenzene C6H4Cl(NO2)

(b) tribromobenzene C6H3Br3

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19.12 Hydrocarbon derivatives19.12 Hydrocarbon derivativeshydrocarbon derivatives –compounds that can be

synthesized from a hydrocarbonthe derivatives contain not only C and H, butadditional elements such as O, N, or halogen

two groups:•compounds do not contain a C=O group•compounds contain a C=O carbonyl group

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19.13 Alkyl halides19.13 Alkyl halidesalkanes react with a halogen in UV light to producean alkyl halide R—X

halogenation UV lightRH + X2 RX + HX (X = Cl, Br)

ex. UV lightCH3CH3 + Cl2 CH3CH2Cl + HCl

UV lightCH4 + Cl2 CH3Cl + HCl

chloromethane

•alkyl halides are primarily used as industrialsolvents ex. CCl4 dry-cleaning solvent

•CH3Cl was once a popular anesthetic•CFCs (chlorinated fluorocarbons) used in

aerosol propellents and refrigerantsdeplete ozone layer

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19.14 Alcohols19.14 Alcoholsalcohol molecules contain a hydroxyl (-OH) groupgeneral formula is ROHalcohols are classified as

primary (1o) secondary (2o) tertiary (3o)H R R| | |

R—C—OH R—C—OH R—C—OH| | |H H R

alcohol molecule can contain two or more –OHgroups if each –OH is attached to a different Catom

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polyhydroxy alcohol is a general term for analcohol that has more than one –OH group permolecule

methanol CH3OH•volatile (bp 65oC), highly

flammable liquid•poisonous, causing

blindness or death•over 8 billion pounds are

manufactured annuallyethanol CH3CH2OH•prepared by fermentation by using sugar as the

raw material and with yeast enzyme –zymaseC6H12O6

zymase 2 CH3CH2OH + 2 CO2•an intermediate in the manufacture of other

chemicals (acetylaldehyde, acetic acid, ethylacetate, diethyl ether)

•a solvent for many organic substances•an ingredient in alcoholic beverages

2-propanol –principal ingredient in rubbing alcoholformulation

ethylene glycol (ethanediol) –used in antifreezes,in manufacture of synthetic fibers

glycerol (1,2,3-pentanetriol) or glycerin –used inmanufacture of polymers and explosives

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19.15 Naming alcohols19.15 Naming alcoholsto name an alcohol by the IUPAC system

ex.

ex. 19.6 name the following alcoholCH3CH2CHCH2CHCH36 5 4| 3 2| 1

CH3 OH2-hexanol 4-methyl-2-hexanol

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ex. 19.7 write the structural formula of 3,3-dimethyl-2-hexanol

1 2 3 4 5 6C—C—C—C—C—C

CH3|

CH3CH2CCH2CH2CH3| |OH CH3

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19.16 Ethers19.16 Ethersethers have the general formula ROR’

saturated ethers have little chemical reactivity, areoften used as solventalcohols (ROH) and ethers (ROR’) are isomeric

ex. ethanol CH3CH2OH bp 78.3oCdimethyl ether CH3OCH3 bp -23.7oC

naming etherscommon name

CH3—O—CH3 dimethyl etherCH3—O—CH2CH3 methyl ethyl ether

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IUPAC system

CH3CH2—O—CH2CH3 ethoxyethaneCH3CH2CH2—O—CH2CH2CH2CH3

propoxybutane

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19.1719.17 AldehydesAldehydes andand ketonesketonesaldehydes and ketones contain carbonyl group

C=Oaldehydes have at least one H atom bonded to thecarbonyl group, ketones have two alkyl (R) oraromatic (Ar) groups bonded to the carbonyl group

aldehyes O O|| ||

R—C—H Ar—C—Hketones O O O

|| || ||R—C—R R—C—Ar Ar—C—Ar

linear expression CH3CHOCH3COCH3

formaldehyde poisonous, irritating gas40% aqueous solution of formaldehyde iscalled formalinmainly used in the manufacture of polymers

acetone and methyl ethyl ketone (MEK) arewidely used as organic solvents

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19.18 Naming19.18 Naming aldehydesaldehydes andand ketonesketonesIUPAC name of aldehyde

-ane -analO||

CH4 methane H—C—H methanalO||

CH3CH3 ethane CH3C—H ethanalCH3 O

6 5 4| 3 2 1||CH3CH2CHCH2CH2C—H 4-methylhexanal

IUPAC name of aldehyde-ane -anone

O O|| 5 4 3 2|| 1

CH3—C—CH3 CH3CH2CH2—C—CH3propanone 2-pentanone

O CH31 2 3|| 4| 5 6CH3CH2—CHCHCH2CH3

4-methyl-3-hexanonenon-IUPAC name

O O|| ||

CH3—C—CH3 CH3CH2—C—CH3dimethylketone, acetone methyl ethyl ketone

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ex. 19.8 write the formulas and the name forthe straight-chain five- and six-carbonaldehydes

O||

CH3CH2CH2CH2C—H pentanalO||

CH3CH2CH2CH2CH2C—H hexanalex. 19.9 give two names for the ketones:

(a) O CH3|| |

CH3CH2CCH2CHCH35-methyl-3-hexanoneethyl isobutyl ketone

(b) O||

CH3CH2CH2C—Ph1-phenyl-1-butanonephenyl propyl ketone

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19.19 Carboxylic acids19.19 Carboxylic acidsorganic acids known as carboxylic acids arecharacterized by the functional group called acarboxyl group

O||

—C—OH —COOH —CO2HIUPAC system to name carboxylic acid

-ane -anoic acidCH4 methane HCOOH methanoic acidCH3CH3 ethane CH3COOH ethanoic acidCH3CH2CH3 propane

CH3CH2COOH propanoic acidcommon names

HCOOH CH3COOH CH3CH2COOHformic acid acetic acid propionic acid

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saturated fatty acids –carboxylic acids have evennumbers of carbon atoms ranging from 4 to 20they exist in combined form in plant and animalfats

aromatic acids

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19.20 Esters19.20 Esterscarboxylic acids react with alcohols in an acidmedium to form ester RCOOR’functional group of ester is –COOR’

O ORC –C

OR’ OR’esterification

naming the esters –the alcohol part is named first,followed by the name of the acid modified toend in -ate

ex. O||

CH3C—OCH3acid alcohol

methyl acetate

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19.21 Polymers19.21 Polymerspolymerization –the process of forming very

large, high-molar-mass molecules fromsmaller units

polymer –the large molecule is calledmonomer –the small repeating unitpolymer containing more than one kind ofmonomer is called copolymermacromoleculeplastics –capable of being molded or pliable

ex. polyethylene PEn CH2=CH2 -CH2CH2[CH2CH2]nCH2CH2-

2500~25000 ethylene molecules joined in acontinuous structurepolyvinylchloride PVC

-(CH2CHCl)-n

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