Organic ChemistryChapter 12

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• Carbon atoms have the ability to link together and form molecules made up of many carbon atoms.

• The branch of chemistry that is the study of carbon-containing compounds is known as organic chemistry ( 有机化学 ).

• 13 million known organic compounds and 100,000 new ones are added annually.

• Only 200,000-300,000 known inorganic compounds.

Question: Why the number of organic compounds is much larger han inorganic compounds, although the elements involved in organic compounds are much less?

12.1 Hydrocarbons ( 碳氢化合物、烃 ) contain only carbon and hydrogen

• Hydrocarbons differ from each other by the number of carbon atoms.

methane CH4 Octane C8H18 polyethylene

Question: What is the feature of C in forming chemical bonding?

• Hydrocarbons differ from each other also by the way carbon atoms connect to each other. Straight-chain hydrocarbon, branched hydrocarbon

• Molecules having the same chemical formula but different structures are called structural isomers ( 结构异构体 ). Structural isomers have different physical and chemical properties. The number of possible structural isomers for a chemical formula increases rapidly as the number of carbon atoms increases: 3 for C5H12, 18 for C8H18, 75 for C10H22, 366,319 for C20H42.

n-pentane iso-pentane Neo- pentane

C

H

H

H

C C C C

H

H H

H

H

H H

H

H C

H

H

H

C C C H

CH3

H H

H

H

H

C

H

H

H

C C H

CH3

CH3 H

H

Other types of structural isomers?

Carbon-based molecules can have different spatial orientations called conformations ( 构象 ).

Fig12.2 three conformation for a molecule of n-pentane. The molecule looks different in each conformation, but the five-carbon framework is the same in all three conformations. In a sample of liquid n-pentane, the molecules are found in all conformations- not unlike a bucket of worms

Hydrocarbons are usually from crude oil by fractional distillation ( 分馏 ).

Fig12.3 a schematic for the fractional distillation of petroleum into its useful hydrocarbon components

12.2 Unsaturated hydrocarbons ( 不饱和烃 ) contai

n multiple bonds

CH3 CH CH CH3

2-butene

Unsaturated hydrocarbonsaturated hydrocarbon

CH3 － CH2 － CH2 － CH3

n-butane

Isomer!

Saturated fat and unsaturated fatThe molecules of saturated fats can pack together, leading to high melting points.The molecules of unsaturated fats can not pack together, leading to low melting points.

stearic acid ， m.p.69℃ oleic acid ， m.p.13℃

Benzene ( 苯 ) and aromatic compounds ( 芳香化合物 )

Fig 12.8 (a) the double bonds of benzene, C6H6, are able to migrate around the ring. (b) for this reason, they are often represented by a circle within the ring

(a) (b)

toluene naphthalene 1,4-dichlorobenzene

Cl

Cl

12.3 Organic molecules are classified by functional group ( 官能团 )

• 醇、酚、醚、胺、酮、醛、酰胺、羧酸、酯

Alcohols contain the hydroxyl group ( 羟基 )

• Methanol: 11 billion pounds were produced annually in USA. Mainly used as solvent and for the preparation of formaldehyde ( 甲醛 ) and formic acid ( 甲酸 ). Ingesting only about 15ml will lead to blindness, 30ml will lead to death.

• Ethanol: produced by biological method (fermentation, 发酵 ) or chemical method.

• The liquid produced by fermentation has an ethanol concentration no more than about 12 percent because at this concentration the yeast begin to die.

Fig 12.11 ethanol can be synthesized from the unsaturated hydrocarbon ethene, with phosphoric acid as a catalyst

Phenols contain an acidic hydroxyl group

• Phenol has antiseptic value, but damages healthy tissue.

O

H

O + H+

Phenoxide ionPhenol(acidic) Hydrogen ion

O O O O

Fig 12.12 the negative charge of the phenoxide ion is able to migrate to select positions on the benzene ring. This mobility helps to accommodate the negative charge, which is why the phenolic group readily donates a hydrogen ion

The oxygen of ether group is bonded to two carbon atoms

• Ethers have lower boiling points and lower solubility in water than the corresponding ethanol due to the weaker interaction between each other and with water.

CO

CH

H H H

H

H

Ethanol: soluble in water, boiling point 78ºC

Dimethyl ether: insoluble in water, boiling point -25ºC

Fig12.14 the oxygen in an alcohol such as ethanol is bonded to one carbon atom and one hydrogen atom. The oxygen in an ether such as dimethyl ether is bonded to two carbon atoms. Because of these difference, alcohols and ethers of similar molecular mass have vastly different physical properties

Diethyl ether: boiling point -25ºC

Fig12.15 Diethyl ether is the systematic name for the “ether” historically used as an anesthetic

Amines form alkaline solutions

H2N NH2

Putrescine (1,4-butanediamine) Cadaverine(1,5-pentanediamine)

NH2H2N

Fig 12.16 low-formula-mass amines like these tend to have an offensive odor

N

N N

N

O

O

H3C

CH3

CH3

+ H3PO4N

N N

N

O

O

H3C

CH3

CH3

H

H2PO4

caffeine-phosphoric acid salt (water-soluble)

Caffeine free-base form (water-soluble)

Phosphoric acid

Fig12.18 all alkaloids are bases that react with acids to form salts. An example is the alkaloid caffeine, shown here reacting with phosphoric acid

Fig12.19 tannins are responsible for the brown stains in coffee mugs or on a coffee drinker’s teeth. Because tannins are acidic, they can be readily removed with an alkaline cleanser. Use a little laundry bleach on the mug, and brush your teeth with baking soda

• Ketones, aldehydes, amides, carboxylic acids and esters all contain a carbonyl group

• Many aldehydes are particularly fragrant. The smells of lemons, cinnamon ( 肉桂 ), almond ( 杏仁 ), and vanilla are due to the aldehydes citral ( 柠檬醛 ), cinnamaldehyde ( 肉桂醛 ), benzaldehyde （苯甲醛） and vanillin ( 香草醛 ).

CH3

CH

H3C CH3

O

CH

OC H

OC

OCH3

OH

O

H

vanillinbenzaldehyde

cinnamonaldehydecitra

Fig 12.21 aldehydes are responsible for many familiar fragrances

Amide

NC

O

Amide group

N

CH2CH3

CH2CH3

O

CH3

Fig12.22 N,N-diethyl-m-toluamide is an example of an amide. Amides contain the amide group, shown hoghlighted in blue

N,N-diethyl-m-toluamide (DEET)

• Carboxylic acids are weak acids.• Salicylic acid ( 水杨酸 ) and acetylsalicylic acid

( 乙酰水杨酸 )

OH

O

O

O

Carboxyl group

ester

Carboxylic acids

acetylsalicylic acid

OH

O

OH

Carboxyl group

Phenolic group

Fig12.24 (a) salicylic acid, found in the bark of the willow tree, is an example of a molecule containing both a carboxyl group and a phenolic group. (b) Aspirin, acetylsalicylic acid, is less acidic than salicylic acid because it no longer contains the acidic phenolic group, which has been concerted to an ester

(a)

(b)

Esters have notable fragrancesstructure Name flavor

Ethyl formate rum

Isopentyl acetate banana

Octyl acetate orange

Ethyl butyrate pineapple

methyl butyrate apple

Isobutyl formate raspberry

Methyl salicylate wintergreen

O

CH

CH2CH3

O

O

C

O

CH3CH3CH2CH2 CH2

O

CH

O

CH2 C

CH3

H

CH3

CH3O

O

O

C

O

CH3CH3CH2CH2

O

C

CH2(CH2)6

O

H3CCH3

O

C

CH2CH2

O

H3CC

CH3

H

CH3

Table12.4 some esters and their flavors

12.4 Organic molecules can link to form polymers

Polymers ( 聚合物 ) are exceedingly long molecules that consist of repeating molecular units called monomers ( 单体 ). Two major types of synthetic polymers: addition polymers ( 加聚型聚合物 ) and condensation polymers ( 缩聚型聚合物 )

polymer

monomer

Fig 12.25 a polymer is a long molecule consisting of many smaller monomer molecules linked together

Addition polymers result from the joining together of monomers

Ethylene monomer

polyethylene

polymerization

Fig 12.26 the addition polymer polyethylene is formed as electrons from the double bonds of ethylene monomer molecules split away and become unpaired valence electrons. Each unpaired electron them joins with an unpaired electron of a neighboring carbon atom to form a new covalence bond that links monomer units together

Table12.5

HDPE and LDPE

(a) Molecular strands of HDPE (b) Molecular strands of LDPE

Fig12.27 (a) the polyethylene strands of HDPE are able to pack closely together, much like strands of uncooked spaghetti. (b) the polyethylene strands of LDPE are branched, which prevents the strands from packing well

Condensation polymers form with the loss of small moleculesNylon 66

Adipic acid

Adipic acid

polymerization

Nylon

Hexamethylenediamine

Reactive ends

Hexamethylenediamine

Fig12.33 adipic acid and hexamethylenediamine polymerize to form the condensation copolymer nylon

Polyethylene terephthalate

Terephthalic acid

Ethylene glycol

polymerization

Polyethylene terephthalate (pet)

Fig12.34 Terephthalic acid and Ethylene glycol Polymerize to form the condensation copolymer Polyethylene terephthalate

Thermoplastic ( 热塑性 ) and thermoset ( 热固性 ) polymers

polymerization

Three reactive ends

formaldehydemelamine

melmac

Fig 12.35 the three reactive groups of melamine allow it to polymerize with formaldehyde to

form a three-dimensional

network

Functional Polymers

Fig12.36 flexible and flat video displays can now be fabricated from polymers