Organic Chemistry: Alkanes, Lecture notes of Organic Chemistry

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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 Drawing Organic Structures Shortcuts make structures easier & faster to draw Butane: C,H, Lewis Structure Carbon Atoms Phat CS H—C—C—C—C—H ANE I I I | Line Structure * Only shows bonds Condensed Structures * 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 CH3-CH)-CH2-CHg CH,CH,CH,CH, CH.(CH,).CH, Alkanes or Paraffins All C atoms are tetrahedral and sp? hybridized (only C-C single bonds) General formula = C,H5,.5 (CHy, CoHs, C3Hg, C4H 49, etc.) Can have linear or branched alkanes pen Csi, wh H3c— e— CH2-CH3 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, Methane 2 CH,CH; Ethane 3 CH,CH,CH, Propane 4 CH3;CH,CH,CH, Butane 5 AN Pentane 6 ANN Hexane 7 AN Heptane 8 ANNO ™ = Octane Q AO ™ Nonane 10 —w—-™O- Dcane Alkyl substituents -CH, Methyl -CH,CH, Ethyl -CH,CH,CH, —-Propyl etc. Root: number of C atoms Suffix: functional group (-ane for alkanes) (-yl for alkyl groups) H H HHH | POET ee een H H H H H Methane Butane CH, CyHio i in | R —C-H R —C-C-C-C | | | | H H HH H Methyl Butyl -CHg -C,H, Where R = any other C atom or arrangement of C atoms Fractional Distillation of Crude Oil Kelter, Carr, Scott, Chemistry A World of Choices 1999, page 429 Crude oil eee ge vapors Condenser 3 Gasoline 38°C =~ Kerosene 150°C —— Heating oil 260°C —F Lubricating oil 315°C — 370°C —e— Steam — > Residue (asphalt, tar) Naming Branched Alkanes (IUPAC) 4-ethyl-3,5-dimethyloctane 3-methyl and 5-methyl = 3,5-dimethyl 1. Root name: name of longest continuous C chain (parent chain) 2 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 R—CH-CH3 3 carbons | | a | , R Kom isopropyl alphabetized as “i” CH3 Isopropyl : “iso” indicates symmetry R—CH2-CH-CH3 R | os isobutyl alphabetized as “i” CH , \, 20 . 4 carbons R—CH-CH2-CH3 R 5s sec-butyl alphabetized as “b” CH3 \ Secondary carbon CH3 30| 0 R GOH Ro tert-butyl alphabetized as “b’ N Tertiary carbon CHs3 Isomers The fat dog shook himself, and then rolled over on the wet rug. OR an’ 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,H,, H H H H Side chain H (branch) (i yee y TT H HA H Main carbon. chain Structural Isomer Practice * On piece of your own paper, draw AND name ALL of the isomers for the following alkanes: Formulas # isomers Pentane Cs5H,, 3 Hexane C,H,, 5 Heptane CH, 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 (CgH,,). There are 18 of them! Structural Isomers: Heptane (C-H,,) AS. heptane o< oN 2,2-dimethylpentane 2-methylhexane AN 2,3-dimethylpentane 3-methylhexane Structural lsomers: Heptane (C-;H,.) AK TT 2,4-dimethylpentane 3-ethylpentane oO AK 3,3-dimethylpentane 2,2,3-trimethylbutane Comparing Structural Isomers (Same formula, different structure) C5H 10 Structure Name Boiling point (°C) AN pentane 36.0 oN 2-methylbutane 27.9 x 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 Cy 9 + he Oy + 4 CO,+_5_H,0 Incomplete Combustion with insufficient O, produces CO ¢ Poor ventilation, cigarettes CyHio + /2 0, > 4 CO+ 5 _H,0 CO is poisonous because it binds to the hemoglobin in the blood, preventing the absorption of O, 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” Textbook Resource Chemistry: An Intro to General, Organic and Biological Chemistry by Timberlake (Green/Tan Book) Sections 10.1-10.6 already covered Currently Section 11.2 (Haloalkanes) Can be used as an outside reference Naming Practice: Haloalkanes Two equal numbering options? Cl 6 3. 9 Number based on alpha order ISSN 5 3 6 F F Cl “rs 2-chloro-5-fluorohexane 2-chloro-4-fluoro-2,3-dimethylpentane OF 2-bromo-3-ethyl-4-iodopentane = 2-bromo-4-chloro-3-isopropylpentane Radical Halogenation: Predict the Product (2) Cl Ch> -X-Cl+HcioR 1-chloropropane. 2-chloropropane OR Remember that any H on the alkane can be replaced by a halogen oe «Brn Yr OR OK Br 1-bromo-2-methylbutane 2-bromo-2-methylbutane Structural lsomer Practice On piece of your own paper, draw AND name ALL of the isomers with the following formulas: Formulas # isomers C,H 4 C,H,Cl, 4 C,H,,Br 8 C,H,Cl, 9 To be honest, there may be more...this is what | found, so try and prove me wrong! Extra Credit to anyone who can find more structures... Some of your drawings may look different, but they are only different structures (isomers) if they also have different names Structural Isomers: C,Hol a oN 1-iodobutane 2-iodobutane MM AL 2-iodo-2-methylbutane 1-iodo-2-methylbutane Structural Isomers: C,H,Cl, Cl Cl oN Aa Cl 1,1-dichloropropane 1,2-dichloropropane ClL HNC SO 1,3-dichloropropane 2,2-dichloropropane Structural Isomers: C,H,Cl, Cl 1,1-dichlorobutane 1 ,2-dichlorobutane Cl AK, CoN 1 ,3-dichlorobutane 1,4-dichlorobutane Structural Isomers: C,H,Cl, Ae Cl 1,1-dichlorobutane ox, clr = 6CI 2,2-dichlorobutane Cl Cl 2,3-dichlorobutane Moo 1,2-dichloro-2-methylpropane ew 1,3-dichloro-2-methylpropane