chapter 18 : organic chemistry
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C. Chapter 18 : Organic Chemistry. Organic chemistry: The study of the compounds of carbon. 85% of all known compounds are organic. Carbohydrates, lipids, proteins, enzymes, nucleic acids, hormones, vitamins, and almost all other chemicals in living systems are organic compounds. - PowerPoint PPT PresentationTRANSCRIPT
Chapter 18 : Organic Chemistry
Organic chemistry:The study of the compounds of carbon.
• 85% of all known compounds are organic.
• Carbohydrates, lipids, proteins, enzymes, nucleic acids, hormones, vitamins, and almost all other chemicals in living systems are organic compounds.
C
< Abundance of the elements in the Earth’s crust.
Why is organic chemistry a separate discipline within chemistry?Vitalism: a “vital force” present in living organisms was believed to be necessary to produce an organic compound.
The experiment of Wöhler in 1828 was the first in a series of experiments that led to the demise of the vital force theory. See reaction below:
NH4Cl AgNCO H2N-C-NH2
OAgCl+ heat +
Ammoniumchloride
Silvercyanate
Urea Silverchloride
Why are Organic Compounds and Inorganic Compounds Different?
• carbon atoms can do some unique things that other atoms cannot
• their bonds are very strong and unreactive• they can attach together in very long chains• they can attach together to form rings• they can form single, double or triple bonds
Hydrocarbons• hydrocarbons contain only C & H• two types - aliphatic or aromatic• insoluble in water
– no polar bonds to attract water molecules• aliphatic hydrocarbons
– may be chains or rings• ring molecules have two less H than chain so that ends
can join• straight chain called the “normal” isomer
Saturated Hydrocarbons
• a saturated hydrocarbon has all C-C single bonds– it is saturated with hydrogens
• saturated aliphatic hydrocarbons are called alkanes
• chain alkanes have the general formula CnH2n+2
Unsaturated Hydrocarbons• unsaturated hydrocarbons have one of more C=C
double bonds or CC triple bonds• unsaturated aliphatic hydrocarbons that contain C=C
are called alkenes– the general formula of a monounsaturated chain alkene is
CnH2n
– remove 2 more H for each additional unsaturation• unsaturated aliphatic hydrocarbons that contain CC
are called alkynes– the general formula of a monounsaturated chain alkyne is
CnH2n-2
– remove 4 more H for each additional unsaturation
Hydrocarbons
8
Uses of HydrocarbonsNumber of
C atoms State Major Uses
1-4 gas heating and cooking fuel
5-7 liquids, (low boiling)
solvents, gasoline
6-18 liquids gasoline
12-24 liquids jet fuel; camp stove fuel
18-50 liquids, (high boiling)
diesel fuel, lubricants, heating oil
50+ solids petroleum jelly, paraffin wax
1-4 gas heating and cooking fuel
5-7 liquids, (low boiling)
solvents, gasoline
6-18 liquids gasoline
12-24 liquids jet fuel; camp stove fuel
18-50 liquids, (high boiling)
diesel fuel, lubricants, heating oil
50+ solids petroleum jelly, paraffin wax
Name LewisStructure
Formula BoilingPoint
MethaneC H
H
H
HCH4 -162°C
EthaneC
H
H
H C H
H
H
CH3CH3 -89°C
PropaneCH
H
H
C
H
H
C
H
H
HCH3CH2CH3 -42°C
ButaneCH
H
H
C
H
H
C
H
H
C
H
H
HCH3CH2CH2CH3 0°C
PentaneCH
H
H
C
H
H
C
H
H
C
H
H
C
H
H
HCH3CH2CH2CH2CH3 36°C
HexaneCH
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
HCH3CH2CH2CH2CH2CH3 69°C
Alkanes• also know as paraffins• aliphatic, saturated• general formula CnH2n+2 for chains • very unreactive• CH3 groups at ends of chains, CH2 groups in
the middle• chains may be straight or branched
– n-alkane = straight chain
Alkanes - Physical Properties• nonpolar molecules, intermolecular
attractions due to induced dipoles• both boiling points and melting points
generally increase as the size of the molecule increases
• insoluble in water, commonly used as nonpolar solvents
• less dense than water, density increases with size
Structural Isomers• isomers are molecules with the same molecular
formula but different arrangements of the atoms– different chemical and physical properties
• structural isomers are isomers in which the atoms are attached differently– different bonding pattern– structural isomers have different physical properties
• structural isomers may give different products in a reaction, though they undergo same types of reactions
Structural Isomers of C4H10Butane, BP = 0°C Isobutane, BP = -12°C
C C C C
H
H
H H
H H
H H
H
HC
H
H
H
H H
H
C HC
CH H
H
Possible Structural IsomersCarbon Content
Molecular Formula
Possible Isomers
4 C4H10 2 5 C5H12 3 6 C6H14 5 7 C7H16 9 8 C8H18 18 9 C9H20 35
10 C10H22 75
Practice – Draw the 3 structural isomers of pentane
C C C C CH
H H H H H
H
HHHHH
C CH
H H H
HHHH
C HC
H H
H
C
C CH
H H
HH
H
H H
H
C
C
H H
H
C
Example – Draw all 9 structural isomers of heptane
• the prefix hept- means 7, so the molecular formula is C7H16
• Start by drawing the carbon skeleton of the straight chain isomer
C C C C C C C
Example – Draw all 9 structural isomers of heptane
• fill in the hydrogens so each C has 4 bonds
C C C C C C CH
H
H
H
H
H
H
H
H
H
H
H
H H
H
H
C C C C CC
C
H
H H H
HH H
H
H H H H
H
HHH
C C C C HC
C
H H H
HH H
H
H H H
HHH
H
H
C
C C CH
H
H
H
H
H
H
H
H
C
CH3
C H
CH3
C CH
H
H
H H
H
H
HCH3
C HC
H
C
CH3
C C CH
H
H
H
H
H
CH3
H
HCH3
C HC
HC C
H
H
H
H
H
H
C
CH3
CH3
C HC
H
H
H
C CH
H
H
H
CH3
H
H
C
CH3
CH3
C H C CC
CH2CH3
H H H
H H H
HH
H
H
C C H
Alkenes• also known as olefins• aliphatic, unsaturated
– C=C double bonds• formula for one double bond = CnH2n
– subtract 2 H from alkane for each double bond• trigonal shape around C
– flat• much more reactive than alkanes• polyunsaturated = many double bonds
Alkynes• also known as acetylenes• aliphatic, unsaturated• CºC triple bond• formula for one triple bond = CnH2n-2
– subtract 4 H from alkane for each triple bond• linear shape• more reactive than alkenes
Aromatics• Benzene
– resonance hybrid– does not react like alkenes
• Reactions are generally substitutions for H
CH
CHCH
CH
CH
Br
CH
CHCH
CH
CHCH
+ Br2 + HBrFeBr3
CH
CHHC
HCCH
CH
CH
CHHC
HCC
C
H
H
Functional Groups• other organic compounds are hydrocarbons in which
functional groups have been substituted for hydrogens
• a functional group is a group of atoms that show a characteristic influence on the properties of the molecule– generally, the reactions that a compound will perform are
determined by what functional groups it has– since the kind of hydrocarbon chain is irrelevant to the
reactions, it may be indicated by the general symbol RCH3—OH
R group functional group
Functional Groups
Alcohols• R-OH• ethanol = CH3CH2OH
– grain alcohol = fermentation of sugars– alcoholic beverages
• proof number = 2X percentage of alcohol– gasohol
• isopropyl alcohol = (CH3)2CHOH– 2-propanol– rubbing alcohol– poisonous
• methanol = CH3OH– wood alcohol = thermolysis of wood– paint solvent– poisonous
Ethers• R– O – R• ether = diethyl ether = CH3CH2OCH2CH3
– anesthetic• to name ethers, name each alkyl group
attached to the O, then add the word ether to the end
diethyl ether
Aldehydes and Ketones• contain the carbonyl group• aldehydes = at least 1 side H• ketones = both sides R groups• many aldehydes and ketones have
pleasant tastes and aromas• some are pheromones• formaldehyde = H2C=O
– pungent gas– formalin = a preservative– wood smoke, carcinogenic
• acetone = CH3C(=O)CH3
– nail-polish remover
O
C
formaldehyde
acetone
Aldehyde Odors and Flavors• butanal = butter
• vanillin = vanilla
• benzaldehyde = almonds
• cinnamaldehyde = cinnamon
O
HC CH2CH2CH3
O
CH
HC
O
C C
H
H
H
OO
HO
HO
Ketone Odors and Flavors• acetophenone = pistachio
• carvone = spearmint
• ionone = raspberries
• muscone = musk
O
CH3C
O CH3
O
H3C
C
CH3
CH2
CH3
CH3H3C O
C CH3CCH
H
Carboxylic Acids• RCOOH• sour tasting• weak acids• citric acid
– found in citrus fruit • ethanoic acid = acetic acid
– vinegar• methanoic acid = formic acid
– insect bites and stings O
OHCH
O
OHCCH3
OH
O
HO C C
CH2 C
C
O
O
OH
OH
CH2
Esters• R–COO–R• sweet odor• made by reacting carboxylic acid with
an alcoholRaCOOH + RbOH RaCOORb + H2O• name alkyl group from alcohol, then
acid name with ate ending– precedence over carbonyls, but not
carboxylic acid– number from end with ester group
O
COH
C CH3
O
O
aspirin
methyl butanoate
Amines• N containing organic molecules• very bad smelling• form when proteins decompose• organic bases• name alkyl groups attached to the N, then add
the word amine to the end
H3C CH2
NH2
ethylamineH3C CH2
NHH3C
ethylmethylamineH2NCH2CH2CH2CH2CH2NH2
cadaverine
putrescineH2NCH2CH2CH2CH2NH2
Amines• many amines are biologically active
– dopamine – a neurotransmitter– epinephrine – an adrenal hormone– pyridoxine – vitamin B6
• alkaloids are plant products that are alkaline and biologically active– toxic– coniine from hemlock– cocaine from coca leaves– nicotine from tobacco leaves– mescaline from peyote cactus– morphine from opium poppies
HO
HO
CH2CH2NH2
dopamine
N
N
CH3
nicotine
Macromolecules• polymers are very large molecules made by
repeated linking together small molecules – monomers
• natural• modified natural polymers• synthetic
– plastics, elastomers (rubber), fabrics, adhesives• composites
– additives such as graphite, glass, metallic flakes
Natural Polymers• polysaccharides
– cellulose (cotton) – starch
• proteins • nucleic acids (DNA)• natural latex rubber, etc• shellac• amber, lignin, pine rosin• asphalt, tar
Nylon• polyamides• good physical properties
– effected by moisture• very good heat resistance• excellent chemical resistance• excellent wear resistance• nylon 6,6 made by condensing
1,6–hexandiamine, H2N–(CH2)6–NH2, with hexandioic acid, HOOC–(CH2)4–COOH
(CH2)6 NH C
O
(CH2)4 C
O
HN