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Unsaturated Hydrocarbons - El Camino College

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					         UNSATURATED HYDROCARBONS

                        HYDROCARBONS

     SATURATED                         UNSATURATED
 PARAFFINS
ALKANES        CYCLOALKANES           ALKENES   ALKYNES




                                            AROMATICS


                  RING WITH CONJUGATED
                     DOUBLE BONDS



       CONJUGATED              ISOLATED
      DOUBLE BONDS           DOUBLE BONDS
             Chemistry 21A                      Dr. Dragan Marinkovic
            UNSATURATED HYDROCARBONS




ethene (ethylene)              propene (propylene)




              1-butene (1-butylene)
                                                     chloroethene (chloroethylene)
                                                             vinyl chloride




          cis-2-butene                          trans-2-butene

               Chemistry 21A                                         Dr. Dragan Marinkovic
          UNSATURATED HYDROCARBONS


                                        cyclopropene
                               C23H46

Muscalure, or cis-9-tricosene, is the
sex pheromone of the female common
       housefly (Musca domestica)


                butadiene



               cyclopentadiene
                                        cycloheptene



                                        cyclooctene
       propan-1,2-diène
             Chemistry 21A                      Dr. Dragan Marinkovic
         UNSATURATED HYDROCARBONS



                                     This is the maximum H/C ratio for
Alkane   R–CH2–CH2–R      CnH2n+2
                                     a given number of carbon atoms.
                                     Each double bond reduces the
Alkene   R–CH=CH–R        CnH2n
                                     number of hydrogen atoms by 2.
                                     Each triple bond reduces the
Alkyne   R–C≡C–R          CnH2n-2
                                     number of hydrogen atoms by 4.




                                     Each ring reduces the
                                            number
                                    of hydrogen atoms by 2




          Chemistry 21A                                      Dr. Dragan Marinkovic
UNSATURATED HYDROCARBONS




                 p-orbitals

                         s-orbitals

          sp2-orbitals

 Chemistry 21A                        Dr. Dragan Marinkovic
            UNSATURATED HYDROCARBONS


In sp2 hybridization the 2s
orbital is mixed with only two of
the three available 2p orbitals:




forming a total of 3 sp2 orbitals with
one p-orbital remaining.                                             π-bond
In ethylene (ethene) the two carbon
atoms form a σ bond by overlapping
two sp2 orbitals and each carbon atom
forms two covalent bonds with
hydrogen by s–sp2 overlap all with
120° angles.
The π bond between the carbon atoms
perpendicular to the molecular plane     Ethylene (ethene), showing
                                             the pi bond in green
is formed by 2p–2p overlap.


               Chemistry 21A                                        Dr. Dragan Marinkovic
               UNSATURATED HYDROCARBONS




Since sp2 hybrid orbitals are always in the same plane, the entire ethylene molecule is planar.


                 Cis-/trans- isomerism are the consequence of the planarity
                of all atoms bonded to double-bonded (C=C) carbon atoms.




                        cis-2-butene                            trans-2-butene

                  Chemistry 21A                                                Dr. Dragan Marinkovic
UNSATURATED HYDROCARBONS


cyclopropene


   All are cis
                            cycloheptene




cis-2-butene     trans-2-butene    methylpropene




 Chemistry 21A                                Dr. Dragan Marinkovic
   UNSATURATED HYDROCARBONS




                                  C18H34O2


Elaidic acid is a trans unsaturated           Oleic acid is a cis unsaturated
fatty acid often found in partially           fatty acid that comprises
hydrogenated vegetable oils.                  55–80% of olive oil.



                         C18H36O2


                         Stearic acid is a saturated fatty acid found in animal fats
                         and is the intended product in full hydrogenation.
                         Stearic acid is neither cis nor trans because it has no double bonds.



       Chemistry 21A                                                       Dr. Dragan Marinkovic
         UNSATURATED HYDROCARBONS


             Elaidic acid           C18H34O2




         Unsaturated fatty acids become rancid relatively quickly.

To combat the instability of unsaturated fatty acids, manufacturers began
to "hydrogenate" them, a process that makes them more stable.
The result was a more solid and longer lasting form of vegetable oil, called
"partially hydrogenated" oil, in which a new type of fatty acid is formed.
This new type of fatty acid is called trans fatty acid.

     Trans fatty acids turn out to increase total cholesterol levels
     and LDL cholesterol levels, and to reduce HDL cholesterol levels.
     In other words, trans fatty acids are detrimental to cardiac health.



            Chemistry 21A                                            Dr. Dragan Marinkovic
            UNSATURATED HYDROCARBONS


Wachenroder isolated β-carotene from carrots in 1831
giving the extracted crystals the name 'carotene'.



                                                       Ripe gac fruits




                               β-carotene




               Chemistry 21A                           Dr. Dragan Marinkovic
         UNSATURATED HYDROCARBONS

Physical properties of alkenes (and alkynes) are very similar to the physical
properties of alkanes with the same number of carbons (and skeletal structure).




           Chemistry 21A                                         Dr. Dragan Marinkovic
         UNSATURATED HYDROCARBONS

             Addition of hydrogen (hydrogenation) across
       carbon-carbon double bond converts alkenes into alkanes.




            Additions of halogens (Cl2, Br2, I2, etc) also called halogenation:
        Bromine and chlorine add readily to ethene to form 1,2-dibromoethane and
1,2-dichloroethane respectively. The reaction occurs even in the dark at room temperature.




            Chemistry 21A                                                    Dr. Dragan Marinkovic
   UNSATURATED HYDROCARBONS

                        Markovnikov's Rule
        In the addition of an unsymmetrical reagent such as
          HCl, HBr and H2O to a double bond of an alkene,
     the hydrogen atom adds to the carbon of the double bond
            with the greatest number of hydrogen atoms.




     1-butene                                 2-bromobutane




1-methylcyclopentene                     1-methylcyclopentanol
      Chemistry 21A                                            Dr. Dragan Marinkovic
              UNSATURATED HYDROCARBONS

                       Poly(ethene) (polythene or polyethylene)

                         an example of addition polymerisation




                 Temperature:     about 200°C
                 Pressure:        about 2000 atmospheres
                 Initiator:       a small amount of oxygen as an impurity
The number of molecules joining up is very variable, but is in the region of 2000 to 20000.


  Low density poly(ethene) is used for familiar things like
  plastic carrier bags and other similar low strength and flexible sheet materials.

      High density poly(ethene) is used to make things like plastic milk bottles
      and similar containers, washing up bowls, plastic pipes and so on.
      Look for the letters HDPE near the recycling symbol.

                 Chemistry 21A                                                 Dr. Dragan Marinkovic
        UNSATURATED HYDROCARBONS
                    Poly(propene) (polypropylene): PP




It has uses in packaging - for example, in plastic film for shrink wrapping food.
There are also medical uses - for example,
in medical tubing and for medical bags and pouches.

           Chemistry 21A                                                 Dr. Dragan Marinkovic
        UNSATURATED HYDROCARBONS

           Poly(chloroethene) is commonly known by
           the initials of its old name (polyvinyl chloride), PVC.




   Poly(tetrafluoroethene): PTFE
You may have come across this under
 the brand names of Teflon or Fluon.

           Chemistry 21A                                             Dr. Dragan Marinkovic
      UNSATURATED HYDROCARBONS

      “it takes alkynes to make a world”
                                            Chemist humor



The chemical bonding in compounds such as
alkynes with triple bonds is explained by sp
hybridization.




In this model the 2s orbital mixes with only
one of the three p-orbitals resulting in two sp
orbitals and two remaining unchanged p
orbitals. The chemical bonding in acetylene
(ethyne) (C2H2) consists of sp–sp overlap
between the two carbon atoms forming a σ
bond and two additional π-bonds formed by
p–p overlap. Each carbon also bonds to
hydrogen in a sigma s–sp overlap at 180°
angles.


         Chemistry 21A                                      Dr. Dragan Marinkovic
                    UNSATURATED HYDROCARBONS
                                                       Two pairs of p-orbitals
                                                       forming a π-bond
                                                 sp-sp s bond


Acetylene is a colorless,
unpleasant-smelling gas (bp -          In acetylene, the H-C≡C bond angles are 180°.
28.1°C), which burns in air to         By virtue of this bond angle, alkynes tend to be rod-like.
produce a very sooty flame.
In the presence of pure oxygen,
however, it burns at very high
                                                   C 2 H2
temperatures (up to 2800°C), and
                                                acetylene (ethyne)
is used in welding and cutting
torches.




                       Chemistry 21A                                                Dr. Dragan Marinkovic
            UNSATURATED HYDROCARBONS




two depictions                           the naturally-occurring
  of propyne                         1-phenylhepta-1,3,5-heptatriyne    the strained cycloheptyne




                 Capillin is an
                 antifungal agent.           Pargyline is an antihypertensive agent, sold
                                             under the trade names Eudatin® and Supirdyl®


             IUPAC Nomenclature
             1. alkane name - “ane” + “yne”



             ethyne (acetylene)                                  butynes
                  Chemistry 21A                                                  Dr. Dragan Marinkovic
    UNSATURATED HYDROCARBONS




R-C≡C-R + H2 & Lindlar catalyst ——> cis R-CH=CH-R

     Chemistry 21A                        Dr. Dragan Marinkovic
            UNSATURATED HYDROCARBONS
       AROMATIC COMPOUNDS




Discovery in 1825 by   In 1858, August Kekule proposed a rapid          Linus Pauling proposed
                       oscillation (I & II) between the 3 C=C and the
 Michael Faraday       3 alternating C-C of hexagonal benzene (C6H6).
                                                                        resonance theory in 1931



C6H 6
                         BENZENE
               Chemistry 21A                                                  Dr. Dragan Marinkovic
UNSATURATED HYDROCARBONS

     All the C-atoms in benzene are sp2-hybridized. Two sp2-hybrid orbitals of each
     C-atom overlap with two sp2-hybrid orbital of two other C-atoms to form sigma
     bonds. In this way there are six sigma bonds are formed between six C-atoms
     which are 120o apart. Remaining six sp2-orbital of six C-atoms overlap with 1s
     orbital of six H-atoms individually to form six sigma bonds. Since sigma bond
     results from the overlap of above said planar orbital, all H and C atoms are in the
     same plane and their generate a hexagonal ring of C-atoms.

  Each C-atom in benzene also has an unhybrid 2pz-orbital containing one electron.
  These 2pz-orbital are perpendicular to the plane of sigma bonds
   Actually these 2pz-orbital produce a pi-molecular orbital containing six electrons.
  One half of this pi-molecular orbital lies above the plane of hexagonal ring and
  remaining half below the ring like a sandwich.
                 The overlap of these 2pz-orbital result in the formation of a fully delocalized
                 pi-bond, which extends all over the six C-atoms of benzene nucleus.




 Chemistry 21A                                                            Dr. Dragan Marinkovic
      UNSATURATED HYDROCARBONS


                         chemical formulas of benzene


π-electrons in benzene
                                Kekule




                           Pauling


         Chemistry 21A                         Dr. Dragan Marinkovic
               UNSATURATED HYDROCARBONS




     heterocyclic                                                        heterocyclic
     aromatic                                                            aromatic
     compound                                                            compound
                                      naphthalene




Why is Trinitrotoluene (TNT) Explosive? Because nitrogen in the nitro
group (NO2) has a charge of +1, the nitro group has a very strong tendency
to withdraw (pull) electrons from the aromatic ring. Therefore, attaching
three nitro groups to a benzene ring leads to an extremely unstable or
explosive compound.
                    Chemistry 21A                                            Dr. Dragan Marinkovic
UNSATURATED HYDROCARBONS




 Chemistry 21A         Dr. Dragan Marinkovic
 UNSATURATED HYDROCARBONS




                    phenylcyclohexane
 C6H5-




C6H5CH2-
                  benzyl alcohol


  Chemistry 21A                         Dr. Dragan Marinkovic
UNSATURATED HYDROCARBONS




 Chemistry 21A         Dr. Dragan Marinkovic
              UNSATURATED HYDROCARBONS


Benzene boils at 80°C - rather higher than other hydrocarbons of similar molecular
size (pentane and hexane, for example). This is presumably due to the ease with
which temporary dipoles can be set up involving the delocalized electrons.

                                  Methylbenzene (toluene) boils at 111°C.
                                  It is a bigger molecule and so the
                                  van der Waals dispersion forces will be bigger.

 You might have expected that methylbenzene's melting point would be higher than benzene's as well,
            but it isn't - it is much lower! Benzene melts at 5.5°C; methylbenzene at -95°C.
 Molecules must pack efficiently in the solid if they are to make best use of their intermolecular forces.
                  Benzene is a tidy, symmetrical molecule and packs very efficiently.
    The methyl group sticking out in methylbenzene tends to disrupt the closeness of the packing.
                  If the molecules aren't as closely packed, the intermolecular forces
                               don't work as well and so the melting point falls.


                   The arenes (aromatic compounds) are insoluble in water.


                  Chemistry 21A                                                         Dr. Dragan Marinkovic
      UNSATURATED HYDROCARBONS




               Benzene is resistant to addition reactions.
  Adding something new to the ring would need you to use some of
the delocalized electrons to form bonds with whatever you are adding.
 That results in a major loss of stability as the delocalization is broken.
      Instead, benzene mainly undergoes substitution reactions –
   replacing one or more of the hydrogen atoms by something new.
           That leaves the delocalized electrons as they were.




         Chemistry 21A                                             Dr. Dragan Marinkovic
                 UNSATURATED HYDROCARBONS

                                                 Polycyclic aromatic hydrocarbons (PAHs)
                                                 are chemical compounds that consist of
                                                 fused aromatic rings and do not contain
                                                 heteroatom or carry substituents.
                                                 PAHs occur in oil, coal, and tar deposits,
                                                 and are produced as byproducts of fuel
                                                 burning (whether fossil fuel or biomass).
                                                 As a pollutant, they are of concern because
                                                some compounds have been identified as
                                                carcinogenic, mutagenic, and teratogenic.
                                                PAHs are also found in foods. Studies have
                                                shown that most food intake of PAHs comes
  from cereals, oils and fats. Smaller intakes come from vegetables and cooked meats.

                                                        mutagen is a physical or chemical
The term carcinogen refers to any substance,
                                                        agent that changes the genetic material
radionuclide or radiation that is
an agent directly involved in the promotion of
cancer or in the increase of its propagation           teratology generally refers to disfiguring
                                                       birth defects or malformations
                    Chemistry 21A                                             Dr. Dragan Marinkovic
               UNSATURATED HYDROCARBONS


However, please, keep in mind that most         aromatic compounds
are beneficial (many medical drugs are aromatic)
and some even essential in our diet and nutrition (some amino acids, vitamins…)




phenylalanine      tryptophan             tyrosine     tyroxine




                                                     Alpha-tocopherol (Vitamin E)
 Pyridoxine
(Vitamin B6)
                Riboflavin (vitamin B2)
                Chemistry 21A                                           Dr. Dragan Marinkovic
UNSATURATED HYDROCARBONS




                 DNA A, C, G, T
                 RNA A, C, G, U

 Chemistry 21A             Dr. Dragan Marinkovic
UNSATURATED HYDROCARBONS




 Chemistry 21A         Dr. Dragan Marinkovic
UNSATURATED HYDROCARBONS




 Chemistry 21A         Dr. Dragan Marinkovic
UNSATURATED HYDROCARBONS




 Chemistry 21A         Dr. Dragan Marinkovic

				
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