Organic Chemistry 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- 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 – The simplest alkyne is acetylene.  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 CH2 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: C4H10 Lewis Structure 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 Condensed Structures CH3CH2CH2CH3 CH3(CH2)2CH3

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

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

Alkanes or Paraffin All C atoms are tetrahedral and sp3 hybridized (only C-C single bonds) General formula = CnH2n+2 (CH4, C2H6, C3H8, C4H10, etc.) Can have linear or branched alkanes C5H12 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 C atoms Alkane Alkyl substituents 1 2 3 4 5 6 7 8 9 10 CH4 CH3CH3 CH3CH2CH3 CH3CH2CH2CH3 methane ethane propane butane pentane hexane heptane octane nonane decane -CH3 -CH2CH3 -CH2CH2CH3 methyl ethyl propyl etc. Root: number of C atoms Suffix: functional group (-ane for alkanes) (-yl for alkyl groups)

H C C H Methane CH4 Butane C4H10 H C ? C H ? R R Methyl -CH3 Butyl -C4H9 Where R = any other C atom or arrangement of C atoms

First Ten Hydrocarbons: Properties Number of Carbon Atoms Molecular Formula Melting Point, oC Boiling Point, oC # of Isomers Name Methane Ethane Propane Butane Pentane Hexane Heptane Octane Nonane Decane 1 2 3 4 5 6 7 8 9 10 CH4 C2H6 C3H8 C4H10 C5H12 C6H14 C7H16 C8H18 C9H20 C10H22 -182.5 -183.2 -187.7 -138.3 -129.7 95.3 90.6 56.8 53.6 29.7 -161.5 -88.6 -42.1 -0.5 36.1 68.7 98.4 125.7 150.8 174.0 1 2 3 5 9 18 35 75

Nonpolar → only London Dispersion Forces IMF Properties of Alkanes Nonpolar → only London Dispersion Forces IMF Larger molecular weight → Stronger London dispersion forces Compound Methane Ethane Propane Butane Pentane Formula CH4 C2H6 C3H8 C4H10 C5H12 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 2 8 4-ethyl-3,5-dimethyloctane 5 4 7 3 1 3-methyl and 5-methyl = 3,5-dimethyl Root name: name of longest continuous C chain (parent chain) Two equally long? Choose the one with more branches Number C atoms in chain, starting at end with first branch Identify substituents, give each a number (C it is connected to) Two or more identical substituents: use prefixes (di-, tri-, tetra-, etc.) List substituents alphabetically before root name Do not alphabetize prefixes 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 R 3 carbons R isopropyl alphabetized as “i” “iso” indicates symmetry R R isobutyl alphabetized as “i” 4 carbons 2o R R 2o sec-butyl alphabetized as “b” Secondary carbon R 3o 3o R tert-butyl alphabetized as “b” Tertiary carbon

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

Naming Practice H H CH3 H C C C H H C H H C H H C H H 4,4-dimethyl Line Structure 1 2 3 4 5 6 1 2 3 4 5 6 H H C H H C H H C H H 4,4-dimethyl hexane 3,3-dimethyl hexane 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 C4H10 2-methylpropane or

Structural Isomer Practice On piece of your own paper, draw AND name ALL of the isomers for the following alkanes: Formulas # isomers Pentane Hexane Heptane C5H12 C6H14 C7H16 3 5 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 (C8H18). There are 18 of them!

Structural Isomers: Pentane (C5H12) 2-methylbutane 2,2-dimethylpropane

Structural Isomers: Hexane (C6H14) 2,3-dimethylbutane 2-methylpentane 2,2-dimethylbutane 3-methylpentane

Structural Isomers: Heptane (C7H16) 2,2-dimethylpentane 2-methylhexane 2,3-dimethylpentane 3-methylhexane

Structural Isomers: Heptane C7H16 2,4-dimethylpentane 3-ethylpentane 3,3-dimethylpentane 2,2,3-trimethylbutane

Comparing Structural Isomers (Same formula, different structure) C5H12 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 13/2 4 5 9/2 4 5 Combustion exothermic reaction alkanes used as fuel source 13/2 4 5 C4H10 + ___ O2  ___ CO2 + ___ H2O Incomplete Combustion with insufficient O2 produces CO Poor ventilation, cigarettes 9/2 4 5 C4H10 + ___ O2  ___ CO + ___ H2O CO is poisonous because it binds to the hemoglobin in the blood, preventing the absorption of O2

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

Radical Halogenation Terms Mechanism How the reaction occurs through multiple steps (most reactions actually occur in many steps) Chain Reaction 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 non-radicals, 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”

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 non-radicals, 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”

Radical Halogenation of Alkanes Reactions of Alkanes Radical Halogenation of Alkanes Mechanism (chain reaction): Step 1 Cl2 ⇌ 2 Cl· Step 2 Cl· + CH4  CH3· + HCl Step 3 CH3· + Cl2  CH3Cl + Cl· Step 4 Cl· + Cl·  Cl2 Type of Step h Initiation Propagation Termination (Free Radicals) Overall reaction: CH4 + Cl2  CH3Cl + 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 Cl2  Cl2  Cl2  Cl2  CH4 CH3Cl CH2Cl2 CHCl3 CCl4 Compound CH3Cl CH2Cl2 CHCl3 CCl4 IUPAC Name chloromethane dichloromethane trichloromethane tetrachloromethane 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