Chapter 19 - Introduction To Organic Chemistry

Chapter 19 Introduction to Organic Chemistry

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19.1 The beginnings of organic chemistry large number of remarkably stable compounds consist of C, H, O and N –organic compounds no organic compounds had been synthesized from inorganic substance before the early 19th century the vital-force theory –organic substances could originate only from living material 1828 Wöhler HCNO + NH3 ╳ NH4+CNONH2 O=C urea NH2 the sources of organic compounds are carboncontaining raw materials –petroleum and natural gas, coal, carbohydrates, fats, and oils

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19.2 The carbon atom C electron structure 1s22s22p4 two stable isotopes: C-12 and C-13 a carbon atom usually forms four covalent bonds with tetrahedral geometry

ex. methane CH4 H .. H:C:H .. H

carbon tetrachloride CCl4 Cl .. Cl:C:Cl .. Cl

one, two, or three pairs of electrons can be shared between two C atoms, forming a single, double, or triple bond . . . . ·C—C· ·C=C· ·C≡C· . . through this bonding ability, long chains of C atoms form by liking one to another 3

organic molecules are classified according to their structural features each class of compounds contain a characteristic atom or group of atoms called a functional group

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19.3 Hydrocarbons hydrocarbons –compounds composed entirely of C and H atoms saturated hydrocarbons have only C—C single bonds unsaturated hydrocarbons contain a double or triple bond between two C atoms, include alkene, alkyne and aromatic compounds general classification of hydrocarbons

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19.4 Alkanes alkanes paraffins saturated hydrocarbons straight- or branched-chain hydrocarbons with only single bonds between the C atoms allowed energies the first member –methane CH4

each member of a series differ in formula from the next member by a CH2 group, the series is known as homologous series the general formula for open chain alkanes is CnH2n+2 combustion reaction generates heat ex. CH4 + 2 O2 CO2 + 2 H2O + 802.5 kJ 6

19.5 Structural formulas and isomerism alkane molecules only contain C—C and C—H bonds alkane molecules are essentially nonpolar, and have little intermolecular attraction and therefore relatively low boiling points three-dimensional structures methane CH4 ethane C2H6 propane C3H8

butane C4H10 normal butane 2-methylpropane

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normal propane bp 0.5oC mp -138.3oC 2-methylpropane bp -11.7oC mp -159.5oC isomerism –the phenomenon that two or more compounds have the same molecular formula the individual compounds are called isomers butane 2 isomers pentane 3 isomers hexane 5 isomers heptane 9 isomers octane 18 isomers nonane 35 ismers decane 75 isomers isomers are compounds with the same molecular formula but different structural formula ex. 19.1 write the structural formulas for three isomers of pentane C—C—C—C—C CH3CH2CH2CH2CH3 C CH3 | | C—C—C—C CH3CHCH2CH3 C CH3 | | C—C—C CH3CCH3 or C(CH3)4 | | C CH3

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19.6 Naming alkanes IUPAC system is generally unambiguous and internationally accepted common alkyl groups CnH2n+1 -ane -yl

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IUPAC rules for naming alkanes

ex.

2-methylbutane

2-methylpentane10

2,3-dimethylbutane

2,2-dimethylbutane

3-methylhexane

2,3,4,6-tetramethylheptane

3-chloro-4-ethyl-2,4-dimethyloctane ex.19.2 write the formulas for (a) 3-ethylpentane 1

2

3

4

5

1

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3

4

5

C—C—C—C—C

CH3CH2CH2CH2CH3 | CH3 (b) 2,2,4-trimethylpentane CH3 1

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3

4

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C—C—C—C—C

1

2 3

4

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CH3CCH2CHCH3 | | CH3 CH3

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ex. 19.3 name these compounds 6

5

4

3

2

1

(a) CH3CH2CH2CH2CHCH3 | CH3 hexane 2-methylhexane 8

7

6

5

4

3

(b) CH3CH2CH2CHCH2CHCH3 | |2 1 CH3CH2 CH2CH3 octane 5-ethyl-3-methyloctane

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19.7 Alkenes and alkynes alkenes contain at least a C=C double bond alkynes contain at least a C≡C triple bond the simplest alkene C2H4 ethene (ethylene) the simplest alkyne C2H2 ethyne (acetylene)

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

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19.8 Naming alkenes and alkynes to name an alkene (or alkyne) by the IUPAC system

ex. 4 3 2 1 CH3CH2CH=CH2 1-butene 4

3

2

1

CH3CH2C≡CH 1-butyne

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3

6

5

2

1

CH3CH=CHCH3 2-butene 4

CH3CH2CH2 |3 2 1 CHCH=CH2 | CH3CH2CH2 3-propyl-1-hexene

CH3 1 2 3 4| 5 6 CH3C ≡C—CH—CH—CH3 | 14 CH3 4,5-dimethyl-2-hexyne

ex. write the structural formulas for (a) 7-methyl-2-octene 8

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6

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4

3

2

1

CH3—CH—CH2—CH2—CH2—CH=CH—CH3 | CH3 (b) 3-hexyne 6

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4

3

2

1

CH3—CH2—C≡C—CH2—CH3

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19.9 Reactions of alkenes alkenes are much more reactive than alkanes addition reaction –a reaction in which two substances join to produce one product hydrogen, halogens, hydrogen halides and water can be added to C=C double bond ex. Pt 25oC CH2=CH2 + H2 CH3—CH3 1 atm

BrCH2—CH2Br

CH2=CH2 + Br—Br

CH3—CH2Cl

CH2=CH2 + HCl H+

CH2=CH2 + HOH

CH3CH2OH

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19.10 Aromatic hydrocarbons benzene and all substances with structures and chemical properties resembling benzene are classified as aromatic compounds benzene C6H6 the structure

although benzene looks as highly unsaturated, it does not readily undergo addition reactions like a typical alkene its typical reaction is substitution reaction: C6H6 + Cl2 Fe C6H5Cl + HCl the modern molecular orbital structure of benzene

chlorobenzene

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19.11 Naming aromatic compounds monosubstituted benzenes

disubstituted benzenes ortho-, meta-, para- (o-, m-, p-)

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trisubstituted benzenes

ex. 19.5 write formulas and names for all possible isomers of (a) chloronitrobenzene C6H4Cl(NO2)

(b) tribromobenzene C6H3Br3

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19.12 Hydrocarbon derivatives hydrocarbon derivatives –compounds that can be synthesized from a hydrocarbon the derivatives contain not only C and H, but additional elements such as O, N, or halogen

two groups: •compounds do not contain a C=O group •compounds contain a C=O carbonyl group20

19.13 Alkyl halides alkanes react with a halogen in UV light to produce an alkyl halide R—X halogenation UV light RH + X2 RX + HX (X = Cl, Br) ex. UV light CH3CH3 + Cl2 CH3CH2Cl + HCl UV light

CH4 + Cl2

CH3Cl + HCl chloromethane

•alkyl halides are primarily used as industrial solvents ex. CCl4 dry-cleaning solvent •CH3Cl was once a popular anesthetic •CFCs (chlorinated fluorocarbons) used in aerosol propellents and refrigerants deplete ozone layer

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19.14 Alcohols alcohol molecules contain a hydroxyl (-OH) group general formula is ROH alcohols 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 –OH groups if each –OH is attached to a different 22C atom

polyhydroxy alcohol is a general term for an alcohol that has more than one –OH group per molecule methanol CH3OH •volatile (bp 65oC), highly flammable liquid •poisonous, causing blindness or death •over 8 billion pounds are manufactured annually ethanol CH3CH2OH •prepared by fermentation by using sugar as the raw material and with yeast enzyme –zymase C6H12O6 zymase 2 CH3CH2OH + 2 CO2 •an intermediate in the manufacture of other chemicals (acetylaldehyde, acetic acid, ethyl acetate, diethyl ether) •a solvent for many organic substances •an ingredient in alcoholic beverages 2-propanol –principal ingredient in rubbing alcohol formulation ethylene glycol (ethanediol) –used in antifreezes, in manufacture of synthetic fibers 23 glycerol (1,2,3-pentanetriol) or glycerin –used in manufacture of polymers and explosives

19.15 Naming alcohols to name an alcohol by the IUPAC system

ex.

ex. 19.6 name the following alcohol CH3CH2CHCH2CHCH3 6 5 4| 3 2| 1 CH3 OH 2-hexanol 4-methyl-2-hexanol

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ex. 19.7 write the structural formula of 3,3dimethyl-2-hexanol 1

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4

5

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C—C—C—C—C—C CH3 | CH3CH2CCH2CH2CH3 | | OH CH3

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19.16 Ethers ethers have the general formula ROR’

saturated ethers have little chemical reactivity, are often used as solvent alcohols (ROH) and ethers (ROR’ ) are isomeric ex. ethanol CH3CH2OH bp 78.3oC dimethyl ether CH3OCH3 bp -23.7oC naming ethers common name CH3—O—CH3 dimethyl ether CH3—O—CH2CH3 methyl ethyl ether 26

IUPAC system

CH3CH2—O—CH2CH3 ethoxyethane CH3CH2CH2—O—CH2CH2CH2CH3 propoxybutane

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19.17 Aldehydes and ketones aldehydes and ketones contain carbonyl group C=O aldehydes have at least one H atom bonded to the carbonyl group, ketones have two alkyl (R) or aromatic (Ar) groups bonded to the carbonyl group aldehyes O O || || R—C—H Ar—C—H ketones O O O || || || R—C—R R—C—Ar Ar—C—Ar linear expression CH3CHO CH3COCH3 formaldehyde poisonous, irritating gas 40% aqueous solution of formaldehyde is called formalin mainly used in the manufacture of polymers acetone and methyl ethyl ketone (MEK) are widely used as organic solvents

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19.18 Naming aldehydes and ketones IUPAC name of aldehyde -ane -anal CH4 methane

O || H—C—H methanal O || CH3C—H ethanal

CH3CH3 ethane CH3 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—CH3 propanone 2-pentanone O CH3 1 2 3|| 4| 5 6 CH3CH2—CHCHCH2CH3 4-methyl-3-hexanone non-IUPAC name O O || || CH3—C—CH3 CH3CH2—C—CH 29 3 dimethylketone, acetone methyl ethyl ketone

ex. 19.8 write the formulas and the name for the straight-chain five- and six-carbon aldehydes O || CH3CH2CH2CH2C—H pentanal O || CH3CH2CH2CH2CH2C—H hexanal ex. 19.9 give two names for the ketones: (a) O CH3 || | CH3CH2CCH2CHCH3 5-methyl-3-hexanone ethyl isobutyl ketone (b) O || CH3CH2CH2C—Ph 1-phenyl-1-butanone phenyl propyl ketone

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19.19 Carboxylic acids organic acids known as carboxylic acids are characterized by the functional group called a carboxyl group O || —C—OH —COOH —CO2H IUPAC system to name carboxylic acid -ane -anoic acid CH4 methane HCOOH methanoic acid CH3CH3 ethane CH3COOH ethanoic acid CH3CH2CH3 propane CH3CH2COOH propanoic acid common names HCOOH CH3COOH CH3CH2COOH formic acid acetic acid propionic acid

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saturated fatty acids –carboxylic acids have even numbers of carbon atoms ranging from 4 to 20 they exist in combined form in plant and animal fats

aromatic acids

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19.20 Esters carboxylic acids react with alcohols in an acid medium to form ester RCOOR’ functional group of ester is –COOR’ O O RC – C OR’ OR’ esterification

naming the esters –the alcohol part is named first, followed by the name of the acid modified to end in -ate ex. O || CH3C—OCH3 acid alcohol methyl acetate

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19.21 Polymers polymerization –the process of forming very large, high-molar-mass molecules from smaller units polymer –the large molecule is called monomer –the small repeating unit polymer containing more than one kind of monomer is called copolymer macromolecule plastics –capable of being molded or pliable ex. polyethylene PE n CH2=CH2 -CH2CH2[CH2CH2]nCH2CH22500~25000 ethylene molecules joined in a continuous structure polyvinylchloride PVC -(CH2CHCl)-n

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