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Chapter 19Chapter 19
Introduction toIntroduction toOrganic ChemistryOrganic 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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