The unique chemistry of carbon Organic Chemistry The unique chemistry of carbon

Learning objectives Describe two reasons for abundance of carbon compounds Distinguish between inorganic and organic carbon and other compounds Distinguish between isomers and non-isomers Describe differences between optical and geometric isomerism Distinguish between aromatic and non-aromatic Identify common functional groups

One element – one branch of chemistry Organic compounds based on carbon: 13 million and rising (fast) 100,000 new compounds synthesized annually All 91 other elements combined: only 300,000 compounds

Factoids about carbon Fairly abundant in earth’s crust – but not enough to explain domination

Highly significant to life Key element in the human organism – and all others

“God’s goof”: The absence of stable mass 5 C and O are abundant because the atom with mass 5 is unstable Otherwise atom building after the Big Bang would have resulted in much heavier elements The thoughts of a cosmological atheist Fred Hoyle: “Some supercalculating intellect must have designed the properties of the carbon atom, otherwise the chance of my finding such an atom through the blind forces of nature would be utterly minuscule….The numbers one calculates from the facts seem to me so overwhelming as to put this conclusion almost beyond question”

Organic and inorganic carbon Inorganic carbon: ionic compounds where carbon is incorporated as carbonate – CO32- Organic carbon: compounds of carbon with itself, hydrogen and other elements – by far the most important

Organic carbon forms a thin canopy Unique (?) conditions on earth that support life Earth’s surface - organic Earth’s crust - inorganic

Vitalism and organic chemistry Inorganic compounds were salts of the earth Stable and easily synthesized Organic compounds were of living organisms Fragile and not easily synthesized Belief in Vitalism posited that only living organisms possessed a vital force necessary to create organic compounds In 1828 urea was synthesized and vitalism was on the way out

Seven ages of man - many ages of a carbon atom Combustion: C + O2  CO2 Neutralization by seawater: CO2 + Ca(OH)2  CaCO3 + H2O Reaction with acid rain: CaCO3 + H2SO4  CO2 Photosynthesis: CO2  Organic compounds (OC) Vegetation decomposes: OC  fossil fuels (FF) Vegetation consumed by animal: OC  new compounds (proteins, DNA etc.) Respiration: sugars  CO2 + energy Industrialization: FF  C, CO2 + energy Manufacturing: FF  Plastics, polymers, drugs etc. Waste disposal Fossil fuels, CO2

Two reasons why carbon is unique Carbon can form four bonds – four valence electrons Carbon forms very strong bonds with itself – chains, rings etc.

Classifying organic compounds

Hydrocarbons are the simplest organic compounds Contain only C and H Simplest is CH4 (natural gas) Intermediate C8H18 (petroleum) Synthetic polymers contain thousands of atoms

Alkanes All bonds are single Saturated No new bonds can be added General formula CnH2n+1

Summary of types

Representing molecules Molecular formula Shows atoms in the molecule Structural formula Shows how they are all connected Condensed structural formula Simplified representation of connections

Naming organic compounds Meth - ane Number of carbon atoms Type of compound

Numbers game: count the carbon atoms in the chain

Saturation bonding: Multiple bonds and unsaturation Saturated: no more bonds can be added Unsaturated: more bonds can be formed More reactive compounds

Alkenes contain double bonds

Going bananas: Ethylene and fruit ripening

Examples of alkynes

Isomerism Same number and type of atoms Different arrangements Hydrocarbons can have straight and branched chains

Isomers simplified Alkane isomers Three isomers of pentane General formula CnH2n+1 Three isomers of pentane C5H12 Five isomers of hexane C6H14

Number of isomers mushrooms as chain length increases CH4 – 1 possibility C2H6 – 1 C3H8 – 1 C4H10 – 2 C5H12 – 3 C8H18 – 18 C10H22 – 75 C20H42 – 366,319

Optical isomerism is a special variation Molecules exhibit handedness – mirror images which are not super-imposable Must have tetrahedral carbon with four different groups attached This carbon is chiral

Isomers and reaction yield Each chiral carbon produces two isomers If there are n chiral carbon atoms there are 2n isomers

Optical isomers are important in nature Amino acids are building blocks of proteins Amino acids are chiral Proteins contain hundreds – thousands of amino acids Getting the correct isomer is a big deal

Geometric isomers: Isomerism and a healthy diet What’s with all this trans fats anyway? Ask a Chicago Alderman Different geometry - same attachments Cis isomers: Don’t pack together Cis isomers have low viscosity - good Trans isomers: Pack together tightly Trans isomers are solids - bad

Aromatic: the stuff of dreams Benzene ring contains 6 C atoms Bonding is resonant – more stable than expected All aromatic compounds contain at least one benzene ring Benzene, C6H6, is one of the most important industrial chemicals

Toxicity of benzene Benzene is regarded as a highly carcinogenic substance Use and disposal of benzene are regulated Compounds containing benzene rings are not necessarily toxic

Functional groups Chemistry of organic compounds is determined by functional groups Functional group is an atom or group of atoms that are different from C Heteroatoms confer very different properties on the substance

Heteroatoms affect physical and chemical properties C2H6 (ethane) is a gas at RT C2H6 is insoluble in water C2H6O (ethanol) is a liquid at RT C2H6O is soluble in water Differences in cohesive forces: O-H bonds are polar, C-H bonds are not

Functionalized hydrocarbons

Chlorocarbons and the environment Important uses – important problems Solvents CH2Cl2 Insecticides DDT Refrigerants CFCs

Alcohols: hic Functional group –OH Polar molecules dissolve in H2O Ethanol: good for your health/bad for your health?

Smoke gets in my eyes: olefactory pleasures of aldehydes C=O is carbonyl group Aldehyde contains RCHO Formaldehyde is a preservative and a product of burning wood Acrolein is a product of barbequing Common smells and flavours

Ketones Ketone is R1R2CO Acetone is a common solvent Smell found in cinnamon Raspberries

Carboxylic acids Commonly found in citrus fruits and any sour foods Formic acid present in ant and bee stings

Esters: sweet aromas and flavours Ester group is R1COOR2 Sweet aroma in pineapples, jasmine Synthetic versions are very common

Ethers Ethers contain R1-O-R2 No -OH bonds Not soluble in water Anesthetics

Amines: the stench of death Amines contain NR1R2R3 Rotting fish Decaying flesh Illicit drugs