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.

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:

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 CC 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 CC are called alkynes the general formula of a monounsaturated chain alkyne is CnH2n-2 remove 4 more H for each additional unsaturation

Hydrocarbons

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

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 C4H10 Butane, BP = 0°C Isobutane, BP = -12°C

Possible Structural Isomers

Practice – Draw the 3 structural isomers of pentane

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

Example – Draw all 9 structural isomers of heptane fill in the hydrogens so each C has 4 bonds

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 Reactions are generally substitutions for H resonance hybrid does not react like alkenes Reactions are generally substitutions for 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 R CH3—OH R group functional group

Functional Groups

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

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 formaldehyde acetone

Aldehyde Odors and Flavors butanal = butter vanillin = vanilla benzaldehyde = almonds cinnamaldehyde = cinnamon

Ketone Odors and Flavors acetophenone = pistachio carvone = spearmint ionone = raspberries muscone = musk

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

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

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

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

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 proteins nucleic acids (DNA) cellulose (cotton) starch proteins nucleic acids (DNA) natural latex rubber, etc shellac amber, lignin, pine rosin asphalt, tar

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 1,6–hexandiamine, H2N–(CH2)6–NH2, with hexandioic acid, HOOC–(CH2)4–COOH ( C H 2 ) 6 N O 4