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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. < Abundance of the elements in the Earth’s crust.
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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:
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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
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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
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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
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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
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Hydrocarbons
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Uses of Hydrocarbons Number 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 jet fuel; camp stove fuel 18-50 (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
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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
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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
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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
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Structural Isomers of C4H10
Butane, BP = 0°C Isobutane, BP = -12°C
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Possible Structural Isomers
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Practice – Draw the 3 structural isomers of pentane
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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
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Example – Draw all 9 structural isomers of heptane
fill in the hydrogens so each C has 4 bonds
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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
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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
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Aromatics Benzene Reactions are generally substitutions for H
resonance hybrid does not react like alkenes Reactions are generally substitutions for H
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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 R CH3—OH R group functional group
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Functional Groups
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Alcohols R-OH ethanol = CH3CH2OH isopropyl alcohol = (CH3)2CHOH
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
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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
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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 formaldehyde acetone
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Aldehyde Odors and Flavors
butanal = butter vanillin = vanilla benzaldehyde = almonds cinnamaldehyde = cinnamon
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Ketone Odors and Flavors
acetophenone = pistachio carvone = spearmint ionone = raspberries muscone = musk
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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
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Esters R–COO–R sweet odor
methyl butanoate R–COO–R sweet odor made by reacting carboxylic acid with an alcohol RaCOOH + 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 aspirin
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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 putrescine ethylamine ethylmethylamine cadaverine
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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
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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
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Natural Polymers polysaccharides proteins nucleic acids (DNA)
cellulose (cotton) starch proteins nucleic acids (DNA) natural latex rubber, etc shellac amber, lignin, pine rosin asphalt, tar
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Nylon polyamides good physical properties very good heat resistance
effected by moisture very good heat resistance excellent chemical resistance excellent wear resistance nylon 6,6 made by condensing ,6–hexandiamine, H2N–(CH2)6–NH2, with hexandioic acid, HOOC–(CH2)4–COOH ( C H 2 ) 6 N O 4
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