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2-1 Chapter 2 saturated hydrocarbons constitutional isomers IUPAC nomenclature conformations cis/trans isomers nomenclature refinement functional groups.

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Presentation on theme: "2-1 Chapter 2 saturated hydrocarbons constitutional isomers IUPAC nomenclature conformations cis/trans isomers nomenclature refinement functional groups."— Presentation transcript:

1 2-1 Chapter 2 saturated hydrocarbons constitutional isomers IUPAC nomenclature conformations cis/trans isomers nomenclature refinement functional groups reactions, sources, properties

2 2-2 Chapter 2 saturated hydrocarbons constitutional isomers IUPAC nomenclature - continued conformations cis/trans isomers nomenclature refinement functional groups reactions, sources, properties cp 42

3 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

4 2-4 Hydrocarbons cp qz

5 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 ( o ) C n H 2n+2 (alkanes) cp qz

6 methane, ethane, propane - 1 structure, but …. C 4 H 10 has 2 forms, same molecular formula but different arrangement - isomers bpt o C o C different connectivity - constitutional isomers cp qz

7 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

8 2-8 Constitutional Isomerism UNIQUE NAME for each? IUPAC nomenclature system cp qz

9 2-9 IUPAC nomenclature: alkane number of carbons (alk) + (ane) saturated HC prefix+suffix cp qz

10 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

11 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

12 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

13 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

14 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

15 2-15 nonane alkane dimethyl ethyl -ethyl-, -dimethylnonane 6-ethyl-3,3-dimethylnonane cp qz

16 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

17 2-17 Cycloalkanes C n H 2n Line-angle drawings cp qz

18 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

19 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

20 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

21 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

22 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

23 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

24 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

25 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

26 2-26 Conformations Torsional strain or eclipsed interaction strain strain (  E  ) arises from nonbonded atoms rotate from staggered to eclipsed conformations cp qz

27 2-27 Conformations Ethane as a function of dihedral angle cp qz

28 2-28 Conformations anti conformation a conformation about a single bond in which the groups lie at a dihedral angle of 180° cp qz

29 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 o calculate total strain - determine the lowest energy conformation ( molecular mechanics ) cp qz

30 2-30 Conformations conformations of butane as a function of dihedral angle cp qz

31 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

32 2-32 Cyclobutane puckering  torsional strain slight  angle strain net - puckered (butterfly) minimum energy conformation but strain energy high cp qz

33 2-33 Cyclopentane “envelope” -  torsional strain slightly  angle strain envelope ~ 1 / 4 th strain energy of cyclopropane cp qz

34 2-34 Cyclohexane - chair conformation Bond bond angles ° Staggered No angle or torsional strain six Hs are axial and six equatorial cp qz

35 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

36 2-36 Equatorial and axial methyl conformations Methylcyclohexane 94 / 6 cp qz

37 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

38 2-38 Cis,Trans Isomerism trans -1,4-dimethylcyclohexane cis -1,4-dimethylcyclohexane cp qz

39 2-39 Cis,Trans Isomerism trans -1,4-dimethylcyclohexane diequatorial-methyl chair more stable by kJ/mol [2 x 7.28] cp qz

40 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

41 2-41 Cycloalkanes (2) Write an IUPAC name for the following: c,d substituent(s) on substituents qz

42 2-42 Nomenclature - IUPAC branched substituents qz

43 tert -butyl-3-isobutylcyclopentane Draw the structure of: trans -1- tert -butyl-3-isobutylcyclopentane OR

44 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

45 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

46 2-46 Alkanes - what are they good for? MAJOR - energy, to do work: some products other - oils, lubricants qz

47 2-47 Sources of Alkanes Natural gas 90-95% methane Petroleum gases (bp below 20°C) naphthas, including gasoline (bp °C) kerosene (bp °C) fuel oil (bp °C) lubricating oils (bp above 350°C) asphalt (residue after distillation) Coal qz

48 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

49 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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