Organic Chemistry The chemistry of carbon and carbonbased

Organic Chemistry: The chemistry of carbon and carbon-based compounds Organic Chemistry in everyday life: Smells & tastes: fruits, chocolate, fish, mint Medications: Aspirin, Tylenol, Decongestants, Sedatives Addictive substances: Caffeine, Nicotine, Alcohol, Narcotics Hormones/Neurotransmitters: Adrenaline, Epinephrine Food/Nutrients: Carbohydrates, Protein, Fat, Vitamins Genetics: DNA, RNA Consumer products: Plastics, Nylon, Rayon, Polyester

Hydrocarbons Simplest class of organic compounds Consist entirely of carbon and hydrogen Four major classes of hydrocarbons: 1. Alkanes — contain only carbon-hydrogen and carbon single bonds 2. Alkenes — contain at least one carbon-carbon double bond 3. Alkynes — contain a least one carbon-carbon triple bond 4. Aromatics — contain rings of six carbon atoms that can be drawn with alternating single and double bonds Alkanes are saturated hydrocarbons; alkenes, alkynes, and aromatics are unsaturated hydrocarbons Copyright 2007 Pearson Benjamin Cummings. All rights reserved.

Hydrocarbons Alkanes – Names of all alkanes end in –ane, and their boiling points increase with more carbon atoms present. – The simplest alkane is methane. – In larger alkanes, carbon atoms are joined in an unbranched chain (straight-chain alkanes) where each carbon atom is bonded to two other carbon atoms. – Alkanes with four or more carbon atoms can have more than one arrangement of atoms. Carbon atoms can form a single, unbranched chain, or the primary chain of carbon atoms can have one or more shorter chains that form branches. – The systematic name for branched hydrocarbons uses the lowest possible number to indicate the position of the branch along the longest straight carbon chain in the structure. Copyright 2007 Pearson Benjamin Cummings. All rights reserved.

Hydrocarbons Alkenes – The simplest alkenes are ethylene and propylene. – Names of alkenes that have more than three carbon atoms use the same stems as the names of alkanes but end in –ene. – More than one structure is possible for alkenes that contain four or more carbons. – The number in the name of an alkene specifies the position of the first carbon atom of the double bond. The name is based on the lowest possible number starting from either end of the carbon chain. Copyright 2007 Pearson Benjamin Cummings. All rights reserved.

Hydrocarbons Alkynes – The simplest alkyne is acetylene. – The names of alkynes are similar to those of the corresponding alkanes but end in –yne. Copyright 2007 Pearson Benjamin Cummings. All rights reserved.

Hydrocarbons Cyclic hydrocarbons – The ends of a hydrocarbon chain are connected to form a ring of covalently bonded carbon atoms. – Cyclic hydrocarbons are named by attaching the prefix cyclo- to the name of the alkane, alkene, or alkyne. – The simplest cyclic alkanes are cyclopropane and cyclobutane – Draw structures of cyclic alkanes by sketching a polygon with the same number of vertices as there are carbon atoms in the ring with each vertex representing a CH 2 unit. Copyright 2007 Pearson Benjamin Cummings. All rights reserved.

Hydrocarbons Copyright © 2007 Pearson Benjamin Cummings. All rights reserved.

Hydrocarbons Aromatic Hydrocarbons – Alkanes, alkenes, alkynes, and cyclic hydrocarbons are called aliphatic hydrocarbons. – Aromatic hydrocarbons are also called arenes and are obtained by the distillation and degradation of highly scented resins from tropical trees. – The simplest aromatic hydrocarbon is benzene. – The chemical behavior of aromatic compounds differs from the behavior of aliphatic compounds. – The general name for a group of atoms derived from an alkane is an alkyl group, and the name of the alkyl group is derived from the name of the alkane by adding the suffix –yl. – Groups of atoms derived from aromatic hydrocarbons are aryl groups. – In general formulas and structures, alkyl and aryl groups are abbreviated as R. Copyright © 2007 Pearson Benjamin Cummings. All rights reserved.

Hydrocarbons Copyright © 2007 Pearson Benjamin Cummings. All rights reserved.

Hydrocarbons • Alcohols – Replacing one or more hydrogen atom of a hydrocarbon with an –OH group gives an alcohol and is represented as R-OH. – The simplest alcohol is methanol (systematic name) or methyl alcohol (common name). – The simplest alcohol derived from an aromatic hydrocarbon is phenol. Copyright © 2007 Pearson Benjamin Cummings. All rights reserved.

Drawing Organic Structures Shortcuts make structures easier & faster to draw Butane: C 4 H 10 Lewis Structure Condensed Structures CH 3 CH 2 CH 3(CH 2)2 CH 3 Carbon Atoms Line Structure • Only shows bonds • C atoms assumed at each end and intersection of bonds • H atoms not shown • Assume 4 bonds to each C • Fulfill C’s 4 bonds by adding H’s

Types of Organic Compounds Classified according to functional group Alkane Alcohol Carboxylic acid Alkene Ether Amine Alkyne Ketone Amide Haloalkane Aldehyde Amino acid

Big Idea in Organic Chemistry Structure controls Function Each functional group has predictable reactivity

Alkanes or Paraffin • All C atoms are tetrahedral and sp 3 hybridized (only C-C single bonds) • General formula = Cn. H 2 n+2 (CH 4, C 2 H 6, C 3 H 8, C 4 H 10, etc. ) • Can have linear or branched alkanes C 5 H 12 1° 3° 2° • Same molecular formula, different structure: structural isomers • Branches are called substituents Primary (1°) carbon atom: bound to one other C atom Secondary (2°) C atom: bound to 2 other C atoms Tertiary (3°) C atom: ” 3 ” Quaternary (4°) C atom: ” 4 ”

Names of Linear Alkanes and Alkyl Substituents # of C atoms Alkane 1 CH 4 2 CH 3 3 CH 3 CH 2 CH 3 4 CH 3 CH 2 CH 3 methane propane butane 5 pentane 6 hexane 7 heptane 8 octane 9 nonane 10 decane Alkyl substituents -CH 3 -CH 2 CH 2 CH 3 methyl propyl etc. Root: number of C atoms Suffix: functional group (-ane for alkanes) (-yl for alkyl groups)

H H H C H H H H Methane CH 4 Butane C 4 H 10 H H H R? C C H C H R ? C C H H H Methyl -CH 3 Butyl -C 4 H 9 Where R = any other C atom or arrangement of C atoms

First Ten Hydrocarbons: Properties Name Number of Carbon Atoms Molecular Formula Melting Point, o. C Boiling Point, o. C # of Isomers Methane 1 CH 4 -182. 5 -161. 5 1 Ethane 2 C 2 H 6 -183. 2 -88. 6 1 Propane 3 C 3 H 8 -187. 7 -42. 1 1 Butane 4 C 4 H 10 -138. 3 -0. 5 2 Pentane 5 C 5 H 12 -129. 7 36. 1 3 Hexane 6 C 6 H 14 -95. 3 68. 7 5 Heptane 7 C 7 H 16 -90. 6 98. 4 9 Octane 8 C 8 H 18 -56. 8 125. 7 18 Nonane 9 C 9 H 20 -53. 6 150. 8 35 Decane 10 C 10 H 22 -29. 7 174. 0 75

Properties of Alkanes Nonpolar → only London Dispersion Forces IMF Larger molecular weight → Stronger London dispersion forces Compound Methane Ethane Propane Butane Pentane Formula CH 4 C 2 H 6 C 3 H 8 C 4 H 10 C 5 H 12 MW 16 30 44 58 72 Boiling point (°C) -164 -88. 6 -42. 1 -0. 5 +36. 0 Linear Alkanes: 1 - 4 C atoms: gas at room temp 5 - 15 C atoms: liquid at room temp >15 C atoms: solid at room temp

Fractional Distillation of Crude Oil Kelter, Carr, Scott, Chemistry A World of Choices 1999, page 429

Naming Branched Alkanes (IUPAC) Octane 4 -ethyl 6 8 7 5 2 4 3 4 -ethyl-3, 5 -dimethyloctane 1 3 -methyl and 5 -methyl = 3, 5 -dimethyl 1. Root name: name of longest continuous C chain (parent chain) Two equally long? Choose the one with more branches 2. Number C atoms in chain, starting at end with first branch 3. Identify substituents, give each a number (C it is connected to) Two or more identical substituents: use prefixes (di-, tri-, tetra-, etc. ) 4. List substituents alphabetically before root name Do not alphabetize prefixes 5. Punctuation: commas separate numbers from each other hyphens separate numbers from names no space between last substituent & root name

Common Names of other Alkyl Substituents Remember that R = any carbon chain 3 carbons R R isopropyl alphabetized as “i” “iso” indicates symmetry R R R isobutyl alphabetized as “i” 4 carbons 2 o R 2 o sec-butyl alphabetized as “b” Secondary carbon R 3 o tert-butyl alphabetized as “b” Tertiary carbon

Naming Practice Expanded Structure H H H Line Structure H H C C H H H C H H butane 2 - methylbutane

Naming Practice H H CH 3 H C C C 6 1 52 43 CH 3 Line Structure H H C H 3 4 H C H 25 H C H 16 H 4, 4 -dimethylhexane 3, 3 -dimethylhexane Lowest sum of numbers is correct

Isomers The fat dog shook himself, and then rolled over on the wet rug. OR The dog shook the fat rug, then rolled over and wet on himself. These two statements use the same words. . . but have very different meanings! Likewise, isomers may have the same formula, but have very different structures…

Structural Isomers of C 4 H 10 2 -methylpropane or

Structural Isomer Practice • On piece of your own paper, draw AND name ALL of the isomers for the following alkanes: # isomers Formulas Pentane C 5 H 12 3 Hexane C 6 H 14 5 Heptane C 7 H 16 9 Some of your drawings may look different, but they are only different structures (isomers) if they also have different names If you complete that, try to draw and name all of the isomers for octane (C 8 H 18). There are 18 of them!

Structural Isomers: Pentane (C 5 H 12) pentane 2 -methylbutane 2, 2 -dimethylpropane

Structural Isomers: Hexane (C 6 H 14) hexane 2, 3 -dimethylbutane 2 -methylpentane 2, 2 -dimethylbutane 3 -methylpentane

Structural Isomers: Heptane (C 7 H 16) heptane 2, 2 -dimethylpentane 2 -methylhexane 2, 3 -dimethylpentane 3 -methylhexane

Structural Isomers: Heptane C 7 H 16 2, 4 -dimethylpentane 3 -ethylpentane 3, 3 -dimethylpentane 2, 2, 3 -trimethylbutane

Comparing Structural Isomers C 5 H 12 Structure (Same formula, different structure) Name Boiling point (°C) pentane 36. 0 2 -methylbutane 27. 9 2, 2 -dimethylpropane 9. 5 More branching → weaker London dispersion forces BP/MP of Linear alkanes > BP/MP of branched alkanes

Reactions of Alkanes Combustion • exothermic reaction • alkanes used as fuel source 13/ 4 CO 2 + ___ 5 H 2 O 2 ___ C 4 H 10 + ___ Incomplete Combustion with insufficient O 2 produces CO • Poor ventilation, cigarettes 9/ 4 CO + ___ C 4 H 10 + ___ 5 H 2 O 2 ___ CO is poisonous because it binds to the hemoglobin in the blood, preventing the absorption of O 2

Radical Halogenation Terms Mechanism How the reaction occurs through multiple steps (most reactions actually occur in many steps) Chain Reactions that occur on their own after some initiating event Free Radicals Atoms that have one free electron—highly reactive

Radical Halogenation Terms • Initiation Step – Step where a bond is split by heat/light, producing free radicals • Propagation Step – Step where free radicals react with nonradicals, producing more free radicals and continuing the “chain reaction” • Termination Step – Step where free radicals react with each other, producing non-radicals and terminating the “chain reaction”

Reactions of Alkanes Radical Halogenation of Alkanes Mechanism (chain reaction): Step 1 Cl 2 ⇌ 2 Cl· (Free Radicals) Type of Step Initiation Step 2 Cl· + CH 4 CH 3· + HCl Propagation Step 3 CH 3· + Cl 2 CH 3 Cl + Cl· Propagation Step 4 Cl· + Cl· Cl 2 Termination h Overall reaction: CH 4 + Cl 2 CH 3 Cl + HCl chloromethane Why not 1 -chloromethane? Halogenated product is a haloalkane Naming: halogen atom is a substituent, replace –ine ending with –o -F fluoro -Cl chloro -Br bromo -I iodo

Radical Halogenation of Alkanes Halogen substitutes for hydrogen in alkane →multiple results Cl 2 CH 4 Compound CH 3 Cl CH 2 Cl 2 CHCl 3 CCl 4 Cl 2 CH 3 Cl Cl 2 CH 2 Cl 2 IUPAC Name chloromethane dichloromethane trichloromethane tetrachloromethane Cl 2 CHCl 3 CCl 4 Common Name methyl chloride methylene chloride chloroform carbon tetrachloride All are liquids at room temperature • Heavy Cl atoms increase LDF • Polar C-Cl bonds – can have polar molecules