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2-1 Chapter 2 saturated hydrocarbons constitutional isomers IUPAC nomenclature conformations cis/trans isomers nomenclature refinement functional groups reactions, sources, properties
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2-2 Chapter 2 saturated hydrocarbons constitutional isomers IUPAC nomenclature - continued conformations cis/trans isomers nomenclature refinement functional groups reactions, sources, properties cp 42
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2-3 Structure Hydrocarbons: Hydrocarbons: compounds only Cs and Hs Saturated hydrocarbon: Saturated hydrocarbon: only single bonds alkane aliphatic hydrocarbon acyclic saturated hydrocarbon open or “linear” chain, saturated hydrocarbon cp qz
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2-4 Hydrocarbons cp qz
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2-5 CH 4 methane (109.5 o bond angles) Structure of alkanes ( aliphatic hydrocarbons, acyclic saturated hydrocarbon): open or “linear” chain, saturated hydrocarbons CH 3 CH 3 ethane (109.5 o ) propane ( 109.5 o ) C n H 2n+2 (alkanes) cp qz
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2-6 2.2 methane, ethane, propane - 1 structure, but …. C 4 H 10 has 2 forms, same molecular formula but different arrangement - isomers bpt. -0.5 o C -11.6 o C different connectivity - constitutional isomers cp qz
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2-7 CH 3 CH 2 CH 2 CH 2 CH 3 C 5 H 12 CH 3 CHCH 2 CH 3 CH 3 CH 3 -C-CH 3 CH 3 3 Note example (problems) pg 59, 60 the same cp qz
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2-8 Constitutional Isomerism UNIQUE NAME for each? IUPAC nomenclature system cp qz
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2-9 IUPAC nomenclature: alkane number of carbons (alk) + (ane) saturated HC prefix+suffix cp qz
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2-10 Nomenclature - IUPAC Parent: Parent: longest (most important) carbon chain substituent: substituent: group off parent chain alkyl group: alkyl group: a substituent carbon gp R- symbol cp qz
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2-11 Nomenclature - IUPAC 1. name (prefix + suffix) longest HC chain ( parent or root name) 2. substituent(s) given name and number propane 2-methylpropane 3. 1 substituent, number chain to give it the lower number cp qz
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2-12 Nomenclature - IUPAC 4. Identical Substituents: number from the end that gives the lower number 2,4-dimethylhexane not 3,5-dimethylhexane Combine like substituents: di-, tri-, tetra-, etc. Use commas to separate position numbers cp qz
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2-13 Nomenclature - IUPAC 5. Different substituents - list them in alphabetical order - number -lower number to the 1 st - substituent [ branch alkyl group R group ] 3-ethyl-5-methylheptane not: 3-methyl-5-ethylheptane 5-ethyl-3-methylheptane cp qz
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2-14 Nomenclature - IUPAC 6. di-, tri-, tetra-, etc. are not used in alphabetization 7. alphabetize substituents and then insert these prefixes 4-ethyl-2,2-dimethylhexane ( not 2,2-dimethyl-4-ethylhexane) cp qz
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2-15 nonane alkane dimethyl ethyl -ethyl-, -dimethylnonane 6-ethyl-3,3-dimethylnonane cp qz
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2-16 C & H Classification, not nomenclature Primary (1°C) Primary (1°C) C bonded to 1 other C and 3Hs (alkane or 2Hs func. gp ) [“methyl” group] Secondary (2°) Secondary (2°) C bonded to 2 Cs (2H) [“methylene” gp.] Tertiary (3°) Tertiary (3°) C bonded to 3 Cs (1H) [“methine” ] Quaternary (4°) Quaternary (4°) C bonded to 4 Cs cp qz
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2-17 Cycloalkanes C n H 2n Line-angle drawings cp qz
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2-18 Cycloalkanes nomenclature cyclo- open-chain name with cyclo- prefix name each substituent on the ring 1 substituent, no number 2 substituents, number by alphabetical priority - list substituents in alphabetical order 3+ substituents, number to give lowest set of numbers - alphabetical order cp qz
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2-19 CYCLOALKANES substituent + alk + ane butyl + ethyl + cyclo + hept+ ane alphabetical numbering priority substituent + cyclo + alk + ane cyclo + 1-butyl-4-ethylcycloheptane cp qz
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2-20 Cycloalkanes Example: (1) Incorrect name: 1,4-dimethyl-3-ethylcyclohexane write the correct name. hint - draw, rename c,d substituent(s) on substituents (2) Write an IUPAC name for the following: cp qz
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2-21 dimethyl Nomenclature nonane cyclopropyl 6-cyclopropyl-2,4-dimethylnonane C C C C C C C H 3 C CH 3 H 3 C H H H H H H H H 3 H H H return to more nomeclature details later cp qz
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2-22 Bicycloalkanes ---- out u Bicycloalkane: u Bicycloalkane: an alkane that contains two rings that share two carbons u Spiroalkane two rings share one carbon Bicyclo[4.4.0]decane (Decalin) Bicyclo[2.2.1]heptane (Norbornane) cp qz
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2-23 Conformations : Conformations : 3-D arrangements of atoms in a molecule from rotation/twisting about single bonds Newman projection: Newman projection: conformational view along a carbon-carbon bond cp qz
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2-24 Conformations Staggered conformation: Staggered conformation: atoms/groups on 1 carbon are as far apart as possible from the atoms/groups on adjacent carbon = 60 o cp qz
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2-25 Conformations Eclipsed conformation: Eclipsed conformation: atoms/groups on 1-C in closet approach to atoms/groups on adjacent C same plane = 0 o cp qz
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2-26 Conformations Torsional strain or eclipsed interaction strain strain ( E ) arises from nonbonded atoms rotate from staggered to eclipsed conformations cp qz
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2-27 Conformations Ethane as a function of dihedral angle cp qz
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2-28 Conformations anti conformation a conformation about a single bond in which the groups lie at a dihedral angle of 180° cp qz
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2-29 Conformations Steric strain(nonbonded interaction strain) Steric strain (nonbonded interaction strain): when atoms separated by 4 (more) bonds are forced closer Angle strain: when a bond angle must compressed or expanded from 109.5 o calculate total strain - determine the lowest energy conformation ( molecular mechanics ) cp qz
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2-30 Conformations conformations of butane as a function of dihedral angle cp qz
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2-31 Cyclopropane angle strain: angle strain: bond angles compressed (109.5° 60°) torsional strain: torsional strain: all 6Hs eclipsed strain energy high cp qz
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2-32 Cyclobutane puckering torsional strain slight angle strain net - puckered (butterfly) minimum energy conformation but strain energy high cp qz
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2-33 Cyclopentane “envelope” - torsional strain slightly angle strain envelope ~ 1 / 4 th strain energy of cyclopropane cp qz
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2-34 Cyclohexane - chair conformation Bond bond angles - 110.9° Staggered No angle or torsional strain six Hs are axial and six equatorial cp qz
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2-35 cyclohexane 2 equivalent chair conformations Flip converts 6 equatorial 6 axial 6 axial Hs in one chair 6 equatorial Hs in other ? cp qz
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2-36 Equatorial and axial methyl conformations Methylcyclohexane 94 / 6 cp qz
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2-37 Cis,Trans Isomerism Stereoisomers - Stereoisomers - compounds with: same molecular formula and connectivity different orientation of atoms in space cis,trans isomers cis,trans isomers - stereoisomers with: 2 groups on same or opposite side of geometric restriction (i.e. ring, double bond). cp qz
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2-38 Cis,Trans Isomerism trans -1,4-dimethylcyclohexane cis -1,4-dimethylcyclohexane cp qz
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2-39 Cis,Trans Isomerism trans -1,4-dimethylcyclohexane diequatorial-methyl chair more stable by 14.56 kJ/mol [2 x 7.28] cp qz
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2-40 cis, trans isomerism cis -1,4-dimethylcyclohexane same energy Note! flip reverses axial-equatorial but……. cis or trans doesn’t change cp qz
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2-41 Cycloalkanes (2) Write an IUPAC name for the following: c,d substituent(s) on substituents qz
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2-42 Nomenclature - IUPAC branched substituents qz
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2-43 1- tert -butyl-3-isobutylcyclopentane Draw the structure of: trans -1- tert -butyl-3-isobutylcyclopentane OR
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2-44 refinement of IUPAC Parent prefix-infix-suffix infix infix - nature of C-C bond(s) suffix suffix - class (functional group) one (more) triple bond(s) one (more) double bond(s) single bonds -yn- -en- -an- Nature of C-C Bond(s) Infix prefix-suffix Chapter 4 qz
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2-45 IUPAC - General en prop-en-e = propene an eth-an-ol = ethanol an but-an-one = butanone an but-an-al = butanal an pent-an-oic acid = pentanoic acid an cyclohex-an-e = cyclohexane yn eth-yn-e = ethyne an eth-an-amine = ethanamine qz
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2-46 Alkanes - what are they good for? MAJOR - energy, to do work: some products other - oils, lubricants qz
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2-47 Sources of Alkanes Natural gas 90-95% methane Petroleum gases (bp below 20°C) naphthas, including gasoline (bp 20 - 200°C) kerosene (bp 175 - 275°C) fuel oil (bp 250 - 400°C) lubricating oils (bp above 350°C) asphalt (residue after distillation) Coal qz
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2-48 Physical Properties Intermolecular forces of attraction (example) strong: ion-ion (Na + and Cl - in NaCl) ion-dipole (Na + and Cl - solvated in aqueous solution) medium:dipole-dipole and hydrogen bonding weak: dispersion forces (very weak electrostatic attraction between temporary dipoles) qz
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2-49 Branching (ball-like) less surface to interact: bpt, mpt, density less Longer or Straight Chains - more interactions along chain. Chapter 4 qz
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