Chapter 11: Alkenes, Alkynes, and Aromatic Compounds

Chemistry 1506

Dr. Hunter’s Class

Section 2 Notes - Page 1/29

Chemistry 1506: Allied Health Chemistry 2

Section 2: Alkenes, Alkynes, and Aromatic Compounds Hydrocarbons with Multiple Bonds

Outline

SECTION

2.1 INTRODUCTION AND NOMENCLATURE OF ALKENES.................................................2

SECTION

2.2 π-BONDS .......................................................................................................................................4

SECTION

2.3 PHYSICAL PROPERTIES .........................................................................................................5

SECTION

2.4 CHEMICAL PROPERTIES: ADDITION REACTIONS .......................................................6

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2.5 ADDITION POLYMERS ............................................................................................................8

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2.6 ALKYNES ...................................................................................................................................13

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2.7 AROMATIC HYDROCARBONS.............................................................................................17

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2.8 AMINO ACIDS HAVING SIMPLE AROMATIC SIDE CHAINS .......................................22

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2.9 AROMATIC REACTIONS .......................................................................................................23

SECTION

2.10 FUSED RING AROMATICS ..................................................................................................25

SECTION

2.11 HETEROCYCLICS (NOT COVERED IN DETAIL)...........................................................26

2000-2002, Dr. Allen D. Hunter, Department of Chemistry, Youngstown State University

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2.1 Introduction and Nomenclature of Alkenes

Ethene = (Ethylene), CH2=CH2

IUPAC Rules Start numbering from the end that gives the double bond the lowest number. Indicate position of double bond(s) by numbers. Use the ene ending Indicated number of double bonds by prefixes (ene, diene, triene, tetraene, etc.) Examples


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Geometric Isomers No free rotation (π-bonds) Experimental observations

cis isomers vs. trans isomers

Examples


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2.2 π-Bonds Bonding: sp2 hybridization for 3 σ-bonds to the three atoms bonded to each carbon pz orbital for π-bond Typical C=C bond distance (i.e., 1.34 Å) and thus shorter than the C-C distance (i.e., 1.54 Å) slightly shorter C-H distance than alkanes


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2.3 Physical Properties Almost identical to Alkanes of same MW Van der Waals forces Slightly higher Mp and Bp Smell (turpentine like) Density Solubility


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2.4 Chemical Properties: Addition Reactions Addition reaction (generic) π-bonds weaker than σ-bonds

Hydrogenation: Addition of H2 or D2 (Pt catalyst)

Addition of Cl2 or Br2 (X2)


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Addition of HX ((HF) HCl, HBr (HI)) Halide Influences Markovnikov Addition

Addition of Water (Hydration) H+ Catalyst Markovnikov


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2.5 Addition Polymers Definition of Addition Polymers No loss of mass Rapid chain growth π-bond opening “Generic” Synthesis Reaction typical monomers are CH2=CH-R

Role of Catalysts Speed reaction but aren’t themselves consumed Highly reactive species


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Reversibility of Reactions Polymerization under low temperatures/high pressures i.e., monomer (liquids or gasses) -> polymer (solids)

Depolymerizations (unraveling) at high temperatures i.e., polymer -> monomer

Molecular Weights and Molecular Weight Distributions High average Molecular Weights Distributions rather than discrete weights

Linear Chains vs. Branched Chains


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Examples Polyethylene, PE, Synthesis CH2=CH2, R = H

Poly(vinyl chloride), PVC, Synthesis CH2=CH-Cl, R = Cl


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Polypropylene, PP, Synthesis CH2=CH-CH3, R = CH3

Polystyrene, PS, Synthesis CH2=CH-C6H5, R = C6H5

Poly(methyl methacrylate), PMMA, Synthesis CH2=C(CH3)(CO2CH3)


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Teflon Synthesis CF2=CF2

Rubber (Polyisoprene) Synthesis CH2=CH-CH=CH2


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2.6 Alkynes Carbon-Carbon Triple Bonds sp hybridized Very Short C≡C Bond distance (i.e., 1.20 Å ), much shorter than the C=C distance (i.e., 1.34 Å) and the C-C distance (i.e., 1.54 Å) Bonding: 1 σ-bond and 2 π-bonds (px and py) slightly shorter C-H distance than alkanes or even alkanes Ethyne = Acetylene, H-C≡C-H

Physical Properties Almost identical to Alkanes/Alkenes of same MW Van der Waals forces Slightly higher Mp and Bp Density Solubility


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Nomenclature yne ending yne > ene in priority of naming Examples


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Alkyne Reactions Generic Reaction Very like Alkenes Normally Double Addition

Hydrogenation: Addition of H2 or D2 (Pt catalyst)

Addition of X2 (Cl2 or Br2)


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Addition of HX (most commonly HCl and HBr) Markovnikov Addition

Addition of H2O (H+ catalyst) Markovnikov Addition Secondary elimination of water from diol gives carbonyl group (aldehyde or ketone)


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2.7 Aromatic Hydrocarbons Sources Coal Tar Coke production Direct separation Start of industrial chemistry Petroleum multiple processing steps Uses Octane enhancers in gasoline Plastics Pigments/Dyes Pharmaceuticals Aromatic:

Properties,

Reactivity,

Alkane/Alkenes/Alkynes)


C/H

Ratios

(cf.

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Substitution Reactions not Addition Reactions (i.e., not like alkenes)

Bonding / Resonance Stabilization


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Nomenclature IUPAC Names Halobenzenes (X = F, Cl, Br, I)

Nitrobenzene (Z = NO2)

Alkylbenzenes (phenylalkanes)


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Common Names (IUPAC) Phenol (Z = OH)

Aniline (Z = NH2)

Toluene (Z = CH3, methylbenzene)

Benzoic Acid (Z = CO2H)


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Multiply Substituted Arenes Numbering Ring Positions

Ortho, Meta, Para, Ipso

As Side Chains (phenyl groups)


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2.8 Amino Acids having Simple Aromatic Side Chains

Generic AA = H2N-CHR-CO2H

Phenyl Alanine (non-polar) R = CH2C6H5 PKU


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2.9 Aromatic Reactions Substitution Reactions Require catalyst "Generic" Z+ Electrophiles

Nitration (Z = NO2, HNO3/H2SO4, TNT)


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Sulfonation (Z = SO3H, H2SO4/SO3)

Halogenation (X = Cl or Br, Cl2/Fe or Br2/Fe)


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2.10 Fused Ring Aromatics Polycyclic Aromatic Hydrocarbons, PAHs Toxicity Naphthalene (C10H8)

Anthracene (C14H10)

Phenanthrene (C14H10)


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2.11 Heterocyclics (Not covered in detail) Replace C-H by Heteroatom Groups such as: N, O, S, etc.

Important in Biomolecules

Pyridine (C5H5N)


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Index of Topics and Vocabulary 1.20 c ................................. 4, 13 1.34 c ................................. 4, 13 Acetylene ................................ 13 Addition .................................. 15 Addition of HX ......................... 7 Addition of Water ..................... 7 Addition Polymers .................... 8 Addition reaction....................... 6 Addition Reactions.................. 18 aldehyde .................................. 16 alkanes....................................... 4 alkenes..................................... 18 Alkenes.................................... 15 Alkylbenzenes ......................... 19 Alkyne Reactions .................... 15 Alkynes ................................... 13 Amino Acids having Simple Aromatic Side Chains .......... 22 Aniline..................................... 20 Anthracene .............................. 25 Arenes ..................................... 21 Aromatic.................................. 17 Aromatic Hydrocarbons .......... 17 Aromatic Reactions................. 23 Benzoic Acid........................... 20 Biomolecules........................... 26 Bonding......................... 4, 13, 18 Bp ........................................ 5, 13 Br2 ....................................... 6, 15 Br2/Fe ...................................... 24 Branched Chains ....................... 9 C≡C Bond distance ................. 13 C/H Ratios............................... 17

C=C bond distance ....................4 C=C distance ...........................13 C10H8 .......................................25 C14H10 ......................................25 C5H5N......................................26 Carbon-Carbon Triple Bonds ..13 carbonyl group.........................16 catalyst.....................................23 Catalysts ....................................8 C-C distance ........................4, 13 CF2=CF2 ..................................12 C-H distance ........................4, 13 CH2=C(CH3)(CO2CH3) ...........11 CH2=CH2 .............................2, 10 CH2=CH-C6H5 .........................11 CH2=CH-CH=CH2 ..................12 CH2=CH-CH3 ..........................11 CH2=CH-Cl .............................10 CH2=CH-R ................................8 chain growth ..............................8 Chemical Properties: Addition Reactions ................................6 cis isomers .................................3 Cl2 ........................................6, 15 Cl2/Fe.......................................24 Coal Tar...................................17 Coke.........................................17 Common Names ......................20 D2 .........................................6, 15 Density.................................5, 13 Depolymerizations.....................9 diene ..........................................2 diol...........................................16


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Double Addition...................... 15 Dyes ........................................ 17 Electrophiles............................ 23 ene ....................................... 2, 14 ene ending ................................. 2 Ethene........................................ 2 Ethylene .................................... 2 Ethyne ..................................... 13 free rotation ............................... 3 Fused Ring Aromatics............. 25 gasoline ................................... 17 Geometric Isomers .................... 3 H+ catalyst ............................... 16 H+ Catalyst ................................ 7 H2 ........................................ 6, 15 H2O.......................................... 16 H2SO4/SO3............................... 24 Halide Influences ...................... 7 Halobenzenes .......................... 19 Halogenation ........................... 24 HBr...................................... 7, 16 H-C≡C-H................................. 13 HCl ...................................... 7, 16 Heteroatom Groups ................. 26 Heterocyclics........................... 26 HF.............................................. 7 HI .............................................. 7 HNO3/H2SO4 ........................... 23 HX....................................... 7, 16 Hydration .................................. 7 Hydrogenation..................... 6, 15 industrial chemistry................. 17 Ipso.......................................... 21 IUPAC Names......................... 19


IUPAC Rules.............................2 ketone ......................................16 Linear Chains ............................9 Markovnikov .............................7 Markovnikov Addition ........7, 16 Meta.........................................21 methylbenzene.........................20 Molecular Weight Distributions 9 Molecular Weights ....................9 monomer....................................9 monomers ..................................8 Mp .......................................5, 13 Naphthalene.............................25 Nitration...................................23 Nitrobenzene ...........................19 Nomenclature ....................14, 19 Octane......................................17 Ortho........................................21 PAH .........................................25 Para..........................................21 PE ............................................10 Petroleum.................................17 Pharmaceuticals.......................17 Phenanthrene ...........................25 Phenol......................................20 Phenyl Alanine ........................22 phenyl groups ..........................21 phenylalkanes ..........................19 Physical Properties ..............5, 13 Pigments ..................................17 PKU .........................................22 Plastics.....................................17 PMMA.....................................11 Poly(methyl methacrylate) ......11


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Poly(vinyl chloride) ................ 10 Polycyclic Aromatic Hydrocarbons ....................... 25 Polyethylene............................ 10 Polyisoprene............................ 12 Polymerization .......................... 9 Polymers.................................... 8 Polypropylene ....................... See Polystyrene.............................. 11 PP .......................................... See Properties ................................ 17 PS ............................................ 11 Pt catalyst ............................ 6, 15 PVC......................................... 10 px ............................................. 13 py ............................................. 13 Pyridine ................................... 26 pz ............................................... 4 Resonance Stabilization .......... 18 Reversibility of Reactions ......... 9 Ring Positions ......................... 21 Rubber..................................... 12 Secondary elimination of water .............................................. 16


Smell..........................................5 Solubility .............................5, 13 sp hybridized ...........................13 sp2 hybridization........................4 Substitution Reactions .......18, 23 Sulfonation ..............................24 Teflon ......................................12 tetraene ......................................2 TNT .........................................23 Toluene....................................20 trans isomers..............................3 triene..........................................2 Van der Waals forces...........5, 13 X2 .........................................6, 15 yne ending ...............................14 Z+ .............................................23 π-bond .......................................4 π-bond opening..........................8 π-bonds................................3, 13 π-Bonds .....................................4 π-bonds weaker than σ-bonds ...6 σ-bond .....................................13 σ-bonds......................................4
