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Introduction to Organic Chemistry Beginning the story of carbon Petroleum – the Primary Source Hydrocarbons - Compounds containing only carbon and hydrogen • “Saturated” hydrocarbons are called alkanes – As many hydrogens in the molecule as possible CH4 Methane Major Sources of Methane • Rice Paddies • Cattle • Decaying Garbage • Natural Gas –B. P. – 161.5 C2H6 CH3CH3 Ethane Ethane Facts • Component of natural gas – B. P. – 88.6 C3H8 CH3CH2CH3 Propane Commercial Uses • LP (liquid petroleum) Gas –Home heating –Cooking –Recreational Uses • Outdoor grills • Gas Fireplaces –B. P. - 42 C4H10 CH3 CH2CH2CH3 CH3(CH2)2CH3 Butane Butane facts • Easily liquefied, vaporized at room temp –B. P. -0.5 • Pocket lighters • Portable, rechargeable torches The rest of the family of alkanes • General Formula: CnH2n+2 • Prefixes: –1 –2 –3 –4 –5 Meth Eth Prop But Pent 6 7 8 9 10 Hex Hept Oct Non Dec Ways to show Molecules • Molecular formula: C2H6 – Shows only the number of each element • Lewis Dot Structure – Shows structure and ALL valence electrons – Must have one dot for each electron HH .. .. H:C:C:H .. .. H H More ways to show molecules • Condensed structural formula – Shows or specifically indicates the location of each element CH3CH3 - Bonds are implied, not shown Still more ways…. • Extended Structural formula – Hybrid of condensed structural and Lewis dot – Replaces pair of electrons with a solid line – Chemists sometimes mix condensed and extended structural formulas, showing some but not all bonds HH | | H-C-C-H CH3 – CH3 | | H H Isomers: • Same molecular formula, different structure and properties Butane: First Hydrocarbon with Isomers CH3CH2CH2CH3 or CH3 CH CH3 CH3 Groups as Substituents • • • • • • Methane Ethane Propane Butane Pentane Etc. becomes becomes becomes becomes becomes methyl ethyl propyl butyl pentyl • The generalized substituent: R- = any alkyl group Numbers of Isomers • • • • • • • 4 carbons – 2 5 carbons – 3 6 carbons – 5 7 carbons – 9 8 carbons – 18 9 carbons – 35 10 carbons - 75 Naming Isomers CH3-CH2-CH2-CH3 1-butane The 1 makes clear that all the carbons are in a line CH3 – CH – CH3 2-methyl propane | CH3 Note: Carbon’s Four Bonds! H | CH3 – C – CH3 | CH3 vs. CH3-CH2-CH2-CH3 On the second carbon in the row, we removed an H, so we could hook on a C and still have 4 and only 4 bonds on each C Systematic names • Developed by IUPAC (International Union of Pure and Applied Chemistry) – Identify and name the longest carbon chain – Number it from one end to the other so that groups attached will have the lowest numbers possible Example 1 2 3 4 5 6 CH3 CH CH2 CH2 CH2 CH3 | CH3 2-methylhexane, not 5-methylhexane More Complex 1 2 3 4 5 6 7 CH3 CH CH CH2 CH2 CH2 CH3 | | CH3 CH3 2,3-dimethylheptane • As we learn “functional groups” (the general name for other atoms or groups we can hook onto carbon), we will practice additional names. Other Hydrocarbon Families • Saturated hydrocarbons = “Alkanes” • Other types of hydrocarbons also group in families • Basically, the prefix of the compound tells the number of carbons, always • The ending of the name tells about the bonding • This makes learning all of them EASY! Unsaturated Compounds: Alkenes • Two or more carbons • At least one double bond – May be located anywhere in the chain of carbon atoms C2H4 CH2=CH2 Ethene (also called ethylene) C3H6 CH2=CH-CH3 Propene (or propylene) C4H8 Multiple Isomers: CH2=CH-CH2-CH3 or CH3-CH=CH-CH3 which can be CH3 CH3 C=C H CH3 or H C=C H or CH3 C=CH2 CH3 H CH3 Butene Isomer Names • n-butene or 1-butene • 2 – butene – Cis (methyls on same side) – Trans (methyls on opposite sides) • Cis and trans are geometric isomers – iso-butene or methyl propene • Vs. 1 and 2 butene, structural isomers General formula for alkenes Cn H2n Then there’s the triple bond: Alkynes • C2H2 • HC CH • Ethyne, also called acetylene General formula for Alkynes: CnH2n-2 Isomers of Alkynes • Positional or structural isomers only (location along chain, branching) – Because, alkynes are linear Cycloalkanes Cyclopropane CH2 – CH2 CH2 Cyclobutane CH2 – CH2 CH2 – CH2 And more….. Cyclopentane CH2 – CH2 CH2 CH2 CH2 Cyclohexane CH2 CH2 CH2 CH2 CH2 CH2 “Boat” CH2 CH2 CH2 CH2 CH2 CH2 “Chair” One more way to illustrate: • Hydrocarbon frameworks can be illustrated by bent lines, each bend being a carbon and its associated hydrogens: = pentane = cyclopropane Aromatics- cyclics with double bonds Benzene – Kekule’s dream CH CH CH CH CH CH CH CH CH CH CH CH As a substituent, abbreviated Ar for “Aryl” Cyclic Aromatics • All Bond lengths are equal • Do not easily undergo addition reactions • “Compromise” structure: CH CH CH CH CH CH Adding Functional Groups • Halogens – Substitution for hydrogen with alkanes, aromatics RCH3 + Cl2 ArH + Cl2 RCH2Cl + HCl ArCl + HCl – Addition to double bonds RCH=CHR + Cl2 RCHCl-CHClR Compounds with Oxygen • Alcohols: R – OH – Addition of water across a double bond or replacement of a halogen • Aldehydes: C=O at the end of a molecule R – C=OH • Ketones: C=O in the middle of a molecule R – C=O – R More Oxygen Compounds • Organic Acids: C=O-OH – The H is capable of ionizing to give R – C=O – O - and H+ • Esters: combine an acid and an alcohol: R – C=O – O – R • Ethers: use a singly-bound oxygen to join two alkyl groups: R–O-R Versatile nitrogen: Amines • A –NH2 group can substitute for a halogen: R – CH2 – NH2 • But also, nitrogen can have one, two, or three alkyl groups hooked to it: – R – NH2 – R2 – NH – R3 – N primary amine (1o) secondary amine (2o) tertiary amine (3o) Amides: Acids plus amines • As long as an amine has at least one hydrogen on nitrogen, it can react with an organic acid to produce an amide and water R – C=O-OH + R’NH2 RC=ONHR’ + H2O Esters: Acids plus alcohols • Similar reaction to Amides: RCOOH + R’OH RCOOR’ + H2O Amino Acids: Building blocks of us • Amino Acids have both an amino group (NH2) and an acid group (COOH). CH3 –CH – COOH | NH2 • Amino Acids link together to make up proteins in the body Basic Organic Reactions • Addition to an olefin (alkene) • CH2=CH2 + HCl CH3-CH2Cl – Hydrohalogenation • CH2=CH2 + Br2 CH2Br-CH2Br – Halogen addition • CH2=CH2 + H2 CH3 – CH3 – Reduction Basic Organic Reactions, con’t • • • • Replacement/substitution CH3-CH2Cl + KOH CH3-CH2OH + KCl CH3-CH2OH + HCl CH3-CH2Cl + H2O CH3CH3 + Cl2 CH3CH2Cl + HCl • Dehydration • CH3-CH2OH CH2=CH2 + H2O Basic Organic Reactions, con’t • Esterification • CH3COOH + CH3OH CH3COOCH3 + H2O • Amidation • CH3COOH + CH3NH2 CH3CONHCH3 + H2O Polymers: Our Plastic World • Addition polymers: link together by combining double-bonded materials – Ethylene CH2=CH2 Polyethylene – Propylene CH2=CH Polypropylene | CH3 More addition polymers Styrene CH2=CH polystyrene | Vinyl Chloride CH2=CHCl - PVC And then Condensation Polymers • Polyester (like Dacron®) HOOC COOH + HOCH2CH2OH • Polyamide (like nylon) H2N (CH2)6 NH2 + HOOC (CH2)4COOH or H2N (CH2)5 COOH