Chapter 19 Introduction to Organic Chemistry

Transcription

1 Chapter 19 Introduction to Organic Chemistry 1

2 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 + NH 3 NH 4+ CNO - NH 2 O=C urea NH 2 the sources of organic compounds are carboncontaining raw materials petroleum and natural gas, coal, carbohydrates, fats, and oils 2

3 19.2 The carbon atom C electron structure 1s 2 2s 2 2p 2 two stable isotopes: C-12 and C-13 a carbon atom usually forms four covalent bonds with tetrahedral geometry ex. methane CH 4 carbon tetrachloride CCl 4 H.. Cl.. H:C:H.. Cl:C:Cl.. H 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

4 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 4

5 19.3 Hydrocarbons 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 5

6 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 CH 4 each member of a series differ in formula from the next member by a CH 2 group, the series is known as homologous series the general formula for open chain alkanes is C n H 2n+2 combustion reaction generates heat ex. CH O 2 CO H 2 O kj 6

7 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 CH 4 ethane C 2 H 6 propane C 3 H 8 butane C 4 H 10 normal butane 2-methylpropane 7

8 normal butane bp 0.5 o C mp o C 2-methylpropane bp o C mp o C 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 write the structural formulas for three isomers of pentane C C C C C CH 3 CH 2 CH 2 CH 2 CH 3 C CH 3 C C C C CH 3 CHCH 2 CH 3 C CH 3 C C C CH 3 CCH 3 or C(CH 3 ) 4 C CH 3 8

9 19.6 Naming alkanes IUPAC system is generally unambiguous and internationally accepted common alkyl groups C n H 2n+1 -ane -yl 9

10 IUPAC rules for naming alkanes ex. 2-methylbutane 2-methylpentane 10

11 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 C C C C C CH 3 CH 2 CH 2 CH 2 CH 3 CH 3 (b) 2,2,4-trimethylpentane CH C C C C C CH 3 CCH 2 CHCH 3 11 CH 3 CH 3

12 ex name these compounds (a) CH 3 CH 2 CH 2 CH 2 CHCH 3 CH 3 hexane 2-methylhexane (b) CH 3 CH 2 CH 2 CHCH 2 CHCH CH 3 CH 2 CH 2 CH 3 octane 5-ethyl-3-methyloctane 12

13 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 C 2 H 4 ethene (ethylene) the simplest alkyne C 2 H 2 ethyne (acetylene) general formula for alkenes: C n H 2n general formula for alkynes: C n H 2n-2 13

14 19.8 Naming alkenes and alkynes to name an alkene (or alkyne) by the IUPAC system ex CH 3 CH 2 CH=CH 2 CH 3 CH=CHCH 3 1-butene 2-butene CH 3 CH 2 C CH CH 3 CH 2 CH butyne CHCH=CH 2 CH 3 CH 2 CH 2 CH 3 3-propyl-1-hexene CH 3 C C CH CH CH 3 CH ,5-dimethyl-2-hexyne

15 ex. write the structural formulas for (a) 7-methyl-2-octene CH 3 CH CH 2 CH 2 CH 2 CH=CH CH 3 CH 3 (b) 3-hexyne CH 3 CH 2 C C CH 2 CH 3 15

16 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 25 o C CH 2 =CH 2 + H 2 1 atm CH 3 CH 3 CH 2 =CH 2 + Br Br BrCH 2 CH 2 Br CH 2 =CH 2 + HCl CH 3 CH 2 Cl CH 2 =CH 2 + HOH H + CH 3 CH 2 OH 16

17 19.10 Aromatic hydrocarbons benzene and all substances with structures and chemical properties resembling benzene are classified as aromatic compounds benzene C 6 H 6 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: C 6 H 6 + Cl 2 Fe C 6 H 5 Cl + HCl the modern molecular orbital structure of benzene chlorobenzene 17

18 19.11 Naming aromatic compounds monosubstituted benzenes disubstituted benzenes ortho-, meta-, para- (o-, m-, p-) 18

19 trisubstituted benzenes ex write formulas and names for all possible isomers of (a) chloronitrobenzene C 6 H 4 Cl(NO 2 ) (b) tribromobenzene C 6 H 3 Br 3 19

20 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 group 20

21 19.13 Alkyl halides alkanes react with a halogen in UV light to produce an alkyl halide R X halogenation RH + X 2 ex. CH 3 CH 3 + Cl 2 UV light UV light UV light RX + HX (X = Cl, Br) CH 3 CH 2 Cl + HCl CH 4 + Cl 2 CH 3 Cl + HCl chloromethane alkyl halides are primarily used as industrial solvents ex. CCl 4 dry-cleaning solvent CH 3 Cl was once a popular anesthetic CFCs (chlorinated fluorocarbons) used in aerosol propellents and refrigerants deplete ozone layer 21

22 19.14 Alcohols alcohol molecules contain a hydroxyl (-OH) group general formula is ROH alcohols are classified as primary (1 o ) secondary (2 o ) tertiary (3 o ) 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 22 C atom

23 polyhydroxy alcohol is a general term for an alcohol that has more than one OH group per molecule methanol CH 3 OH volatile (bp 65 o C), highly flammable liquid poisonous, causing blindness or death over 8 billion pounds are manufactured annually ethanol CH 3 CH 2 OH prepared by fermentation by using sugar as the raw material and with yeast enzyme zymase C 6 H 12 O zymase 6 2 CH 3 CH 2 OH + 2 CO 2 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 glycerol (1,2,3-pentanetriol) or glycerin used in 23 manufacture of polymers and explosives

24 19.15 Naming alcohols to name an alcohol by the IUPAC system ex. ex name the following alcohol CH 3 CH 2 CHCH 2 CHCH CH 3 OH 2-hexanol 4-methyl-2-hexanol 24

25 ex write the structural formula of 3,3- dimethyl-2-hexanol C C C C C C CH 3 CH 3 CH 2 CCH 2 CH 2 CH 3 OH CH 3 25

26 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 CH 3 CH 2 OH bp 78.3 o C dimethyl ether CH 3 OCH 3 bp o C naming ethers common name CH 3 O CH 3 dimethyl ether 26 CH 3 O CH 2 CH 3 methyl ethyl ether

27 IUPAC system CH 3 CH 2 O CH 2 CH 3 ethoxyethane CH 3 CH 2 CH 2 O CH 2 CH 2 CH 2 CH 3 propoxybutane 27

28 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 CH 3 CHO CH 3 COCH 3 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 28

29 19.18 Naming aldehydes and ketones IUPAC name of aldehyde -ane -anal O CH 4 methane H C H methanal O CH 3 CH 3 ethane CH 3 C H ethanal CH 3 O CH 3 CH 2 CHCH 2 CH 2 C H 4-methylhexanal IUPAC name of aldehyde -ane -anone O O CH 3 C CH 3 CH 3 CH 2 CH 2 C CH 3 propanone 2-pentanone O CH CH 3 CH 2 CHCHCH 2 CH 3 4-methyl-3-hexanone non-iupac name O O CH 3 C CH 3 CH 3 CH 2 C CH29 3 dimethylketone, acetone methyl ethyl ketone

30 ex write the formulas and the name for the straight-chain five- and six-carbon aldehydes O CH 3 CH 2 CH 2 CH 2 C H pentanal O CH 3 CH 2 CH 2 CH 2 CH 2 C H hexanal ex give two names for the ketones: (a) O CH 3 CH 3 CH 2 CCH 2 CHCH 3 5-methyl-3-hexanone ethyl isobutyl ketone (b) O CH 3 CH 2 CH 2 C Ph 1-phenyl-1-butanone phenyl propyl ketone 30

31 19.19 Carboxylic acids organic acids known as carboxylic acids are characterized by the functional group called a carboxyl group O C OH COOH CO 2 H IUPAC system to name carboxylic acid -ane -anoic acid CH 4 methane HCOOH methanoic acid CH 3 CH 3 ethane CH 3 COOH ethanoic acid CH 3 CH 2 CH 3 propane CH 3 CH 2 COOH propanoic acid common names HCOOH CH 3 COOH CH 3 CH 2 COOH formic acid acetic acid propionic acid 31

32 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 32

33 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 CH 3 C OCH 3 acid alcohol methyl acetate 33

34 19.21 Polymers 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 CH 2 =CH 2 -CH 2 CH 2 [CH 2 CH 2 ] n CH 2 CH ~25000 ethylene molecules joined in a continuous structure polyvinylchloride PVC -(CH 2 CHCl)- n 34

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