ALKENES and it Functional Groups Compund

Organic Chemistry : Organic Compound. Alkenes and derivatives

1. Unsaturated
Hydrocarbons:
ALKENES
RONIELENE M. ABUG
Organic Chemistry
Central Philippines State University -Main Campus

2. Table of contents.
01 | Properties 02 | Structure
03 |
Nomenclature
04 | Reactions
05 | Uses or
Application
06 | Activity

3. Alkenes
areaclassofunsaturatedhydrocarbonscharacterizedbyatleastone
carbon-carbondoublebond.
classifiedasunsaturatedhydrocarbons(compoundswithdoubleortriple
carbon-carbonbondsthatenablethemtoadduphydrogenatoms)
alsocalledasolefins(compoundmadeupofhydrogenandcarbonthat
containsoneormorepairsofcarbonatomslinkedbyadoublebond)
Mathematically,thiscanbeindicatedbythefollowinggeneralformula:
C
nH
2n

4. PROPERTIES

5. Physical state
The members containing two or four carbon
atoms are gases, five to seventeen, liquids,
eighteen onwards, solids at room
temperature and they burn in air with a
luminous smoky flame.
Density
Alkenes are lighter than water.
Solubility
Alkenes are insoluble in water and soluble
in organic solvents such as benzene etc.
Boiling point
The boiling points of alkenes show a gradual
increase with an increase in the molecular
mass or chain length, this indicates that the
intermolecular attractions become stronger
with the increase in the size of the molecule.
General Properties
of
Alkenes

6. Physical Properties of Alkenes
Alkenesexistnaturallyinallthreestates.Thefirstfouralkenesaregases,andthenext
thirtteenareliquids.Alkeneshigherthantheseareallsolids.
Allalkenesareinsolubleinwater,duetotheweakvanderWaalforces.
Butalkenesaresolubleinorganicsolventslikebenzeneoracetonebecauseherethevander
Waalforceswillbereplacedbynewones,makingalkenesfullysoluble.
Theboilingpointsofalkenesdependontheirmolecularstructure.Thebiggertheirmolecular
chainthehighertheboilingpoints.Sothehigheralkeneshaveveryhighboilingpoints
Thepolarityofalkeneswilldependontheirfunctionalgroups

7. Chemical Properties of Alkenes
Alkenesbelongtothefamilyofhydrocarbonscontainingadoublebondbetween
carbon-carbonatoms.
Alkenesarelessstablethanalkanesandmorestablethanalkynes.
Alkenesexistinallthreesolid-liquidandgaseousstates.
AlkenesarelesssolubleinwaterduetoweakVan-Der-Waalforces
Theboilingpointofalkenesdependsonthemolecularstructure,thelongerthe
molecularchain,thehigherwillbeitsboilingpoint.
Functionalgroupsareresponsibleforthepolarityofalkenes.

8. STRUCTURE

9. The structure of alkenes
In ALKANES, the four sp
3
orbitals repel each other into a
tetrahedral arrangements.
In ALKENES, the three sp
2
orbitals repel each other into a
planar arrangement and the 2p
orbital lies at a right angle to
them.

12. The general structure of
an alkene

13. The structure of
ethylene, the simplest
alkene

14. An alkene is said to be substituted when the hydrogen
atoms at each end of the C=C bond are replaced by
alkyl (or alkyl halide) groups.

15. Kekulé Structure
They are similar to Lewis
structures with all the bonding
electrons shown in short lines and
all the atoms included as element
symbols. However, the lone pair
electrons are left out in Kekulé
structures, which is the major
difference between Kekulé
structures of organic compounds
and Lewis structures.

16. CondensedStructure Formula
The C-H bonds are omitted, and all the H
atoms attached to a certain carbon (or
other atoms) are usually shown as a group
like CH3, CH2, NH2, and OH. The C-C
bond sometimes can be omitted as well .
Usually, if the structure has a branch, the
bonding between the parent structure to
the branch needs to be shown with a short
line.
CH
2=CHCH
2CH
3
CH
2=CH-CH
2-CH
3

17. Short-Line Structure
Formula
The structure drawing can be further
simplified by a short-line structure (or “bond-
line structure”, “skeletal formula” in other
books) with most atoms omitted; this is also
a very common type of structure formula
used in organic chemistry because of its
simplicity.
To apply and interpret the short-line
structures correctly, it is important to clearly
understand the conventions of this type of
drawing.

19. NOMENCLATURE

20. Did you know?
There are two ways of naming alkanes!
1. Common/Trivial name system
2. IUPAC Nomenclature
(International Union of Pure and Applied Chemistry)

21. Common/Trivial name system
In this system, alkanes are named by changing
the ending “ane”of corresponding alkanes by
“ylene”.
The position of the double bond is indicated by Greek
letters α,β,γetc
The first member of the homologous series of
alkenes is: CH2 known as methene, but has a very
short life.
01
02
03

24. IUPAC Nomenclature
Name the parent hydrocarbon by locating the longest carbon
chain that contains the double bond and name it according
to the number of carbons with the suffix -ene.
01

25. 02
a.)Number the carbons of the parent chain so the double
bond carbons have the lowest possible numbers.
b.)If the double bond is equidistant from each end, number
so the first substituent has the lowest number.

26. 03
04
Write out the full name, numbering the substituents
according to their position in the chain and list them in
alphabetical order.
Indicate the double bond by the number of the first alkene
carbon.
05
If more than one double bond is present, indicate their
position by using the number of the first carbon of each
double bond and use the suffix -diene (for 2 doublebonds),
-triene (for 3 double bonds),
-tetraene (for 4 double bonds), etc.

27. 06
a.)Cycloalkenes are named in a similar way. Number the
cycloalkene so the double bond carbons get numbers 1 and 2,
and the first substituent is the lowest possible number.
b.)If there is a substituent on one of the double bond
carbons, it gets number 1.

28. REACTIONS

29. 01
Addition reactions of
alkenes
Hydrogenation: Addition of hydrogen
Doublebondofalkeneundergoes theaddition of
hydrogen inthepresence ofametalcatalyst.This
hydrogenationisanexothermicreactionastwosigmabonds
(C–H)areformedattheexpenseofonesigmabond(H–
H)andpibondofcarbon-carbon.Theamountofheat
evolvedwhenonemoleofanunsaturated compoundis
hydrogenatediscalledheatofhydrogenation.

30. 02Electrophilic addition reactions of
alkenes
Additionofhydrogenhalides
Thepibondisnotasstrongasthesigmabondandthe
electroncloudaboveandbelowtheplaneispolarizable.
Thisway,adoublebondcanactasanucleophile.Atypical
exampleofthismechanismistheadditionofhydrogen
halides whereprotonfromstrongacidmayyielda
carbocation.Inthepresence ofstrong nucleophile,
carbocationundergoeselectrophilic additiontothedouble
bondsite.

31. Halogenation:Additionofhalogens
Alkenesareeasilyconverted byhalogens toalkyl
halideswheretwohalogenatomsareattached totwo
carbonsatadjacentpositions.Thereactionisrelatively
easilycarriedoutatroomtemperature anddoesnot
requirelight.Tworeactantsaremixedinaninertsolvent
suchascarbontetrachloride.

32. Intheexampleofbrominationofethene,bothreactants
arenotpolarbutcanbepolarized.Henceinduceddipole
creates slightpolarity atbromine atomsofbromine
molecule.Thereaction proceeds withanelectrophilic
mechanismformingapositivelychargedintermediate which
subsequently withotherbromineatomsgivessaturated
dibromoethane.Twobrominesareattachedtotwoadjacent
carbons,suchhalidesareknownasvicinaldihalides.

33. Theadditionofbromineisanextremelyusefultool
employedtodetectthepresenceofdoublebondsinan
unknown organic compound.Bromine solution incarbon
tetrachloride isred,theaddition ofanunsaturated
molecule rapidly decolourizes bromine.This isa
characteristic testtoconfirmthepresenceofacarbon–
carbondoublebond.
Iodinedoesnotreactwithalkenesatall.

34. AdditionofWater
Wateraddstoreactivealkenesinthepresenceofanacid
toformalcohol.Thisreactioniscarriedoutindiluteacids
e.g.50%water:H2SO4solution.Thisadditionalreactionhas
significantindustrialimportanceinmanufacturingalcohols.

35. Additionofsulfuricacid
Thisisanother methodofconverting alkenes into
alcohols.Alkenesreactwithcoldconcentratedsulfuricacid
toformalkylhydrogensulfateester.Thisproductisformed
bytheadditionofhydrogenofacidtoonecarbonofalkene
doublebondandbisulfateiontotheother.Ondilutingthe
reaction mixtureandwarmingitup,sulfateesteris
hydrolyzedtoformalcohol.Thismethodisusedforlarge-
scalemanufacturingofalcohols.

36. 03Oxidation reactions
Hydroxylation:Formationof1,2diols
Alkenesareoxidizedwithcertainoxidizingagentssuch
aspotassiumpermanganatetoaddhydroxylgroupsatdouble
bondsofalkenes.Thisadditionofhydroxylgroupsis
calledhydroxylation anditgivesvicinaldiols.Thisis
animportantreactionforthesynthesisofdiols.
Thisreaction formsthebasisofaveryuseful
analyticaltestknownastheBaeyertesttodetectthe
presenceofdoublebond(unsaturation) inamolecule.

37. Epoxidation
Three-memberedringscontainingoxygenarecalledepoxide.
Theepoxideformationisamajororganicreaction.Theyare
formedbythereaction ofalkenes withasourceof
electrophilic oxygen.Themostimportant epoxideatan
industrialscaleisactuallythesimplestofall,ethylene
oxide.Ithasnumerousindustrialapplicationsandisformed
bycatalyticoxidationofethenebyair.

38. Ozonolysis
Ozone(O3)isatriatomicmoleculeandisapowerful
electrophile.Itundergoesreactionwithalkenescleaving
bothsigmaandpicarbon-carbonbonds.Thisreactionisknown
asozonolysis orozonation andtheproductsarecalled
ozonides.
Ozoneispassedthroughanalkenesolutioninaninert
solvent.Thereactionleavesviscousozonidethatcannotbe
purifiedasitisunstableandexplosiveinnature.Ozonide
isimmediatelytreatedwithwaterandinthepresenceofa
reducing agenttoformcarbonyl compounds (ketone or
aldehyde).

39. 04Polymerization
Polymerization isachemicalreactionwheresmallunits
orgroupscombinetogethertomakeabiggermolecular
material.Thesmallsub-units(orbuildingblocks)are
calledmonomers whiletheresultant biggermolecular
weightmaterialiscalledpolymerandtheprocessis
calledpolymerization.Duringpolymerization, thousandsof
monomersunitetogethertomakeaverylargemolecule.
Etheneisanimportantfeedstockforthesynthesisof
variouspolymersinthechemicalindustry.PVCandPEare
commonlyknownwordsinoureverydaylife.PVCstandsfor
polyvinylchloridewhilePEispolyethylene.Bothare
plasticsandareinusearoundus.

40. Polyethyleneismadeupofthepolymerization ofnumerous
ethyleneunits.Thereactionproceedsviaafreeradical
mechanismwhereoxygenorperoxideisusedtoinitiatethe
chemicalreaction.
Anothergoodexampleofpolymerization isthesynthesisof
polyvinylchloride.Here,etheneundergoeshalogenationfirst
andthensubsequent polymerization toformourpopular
plastic.
Similarly, otherexamples arepolyvinyl alcohol and
polystyreneusedinmanyindustrialapplications.

41. USES/APPLICATION

42. Alkenes are used for a variety of
purposes.
Following are some of them:
In combination with
oxygen, ethylene is
used as oxyethylene
flame which is used
for cutting and
welding metals.
Ethylene is also used
to manufacture
polythene, which in
turn is used to
prepare pipes,
bottles, toys, bags,
etc.
Ethylene is used for
the artificial
ripening of fruits
and is sometimes used
as an anaesthetic.
Alkenes are used as
starting materials in
the preparation of
several compounds
like alkyl halides,
alcohols, glycols,
dioxane, etc.

43. Ethene on
polymerization
gives
polyethylene, a
well-known
plastic.
Limonene, containing
two carbon-carbon
double bonds, is
responsible for the
smell of lemons and
oranges.
Ethene is also
responsible for the
germination of seeds,
flower maturation and
ripening offruits
(e.g. tomatoes).
β−phellandrene
is present in
eucalyptus oil
Italsoplays an important role in our
everyday life.

44. Natural rubber is
obtained from a basic
unit, isoprene, which
contains two carbon-
carbon, double bonds.
The orange-pink
colour of carrot is
due to the presence
of β−carotene
that contains eleven
carbon-carbon double
bonds.
Many edible oils
consist of fatty
acids that have one
or more carbon-carbon
double bonds (e.g.
oleic acid).
The flavour of ginger
is due to the
presence of
zingiberene, which
contains three
carbon-carbon double
bonds.

45. The skin of an apple
contains a compound
known as α−farnesene,
which contains four
carbon-carbon double
bonds.
β−carotenedecomposes to form
vitamin A, which undergoes a number
of chemical reactions in presence of
light which is responsible for the
ocular activity.
The chemistry of
vision of all
animals is
closely related
to the chemistry
of Alkenes.

46. ACTIVITY

47. 1. Briefly describe the
properties of alkenes.

48. 2. Without consulting
tables, arrange the
following alkenes in
order of increasing
boilingpoint:

49. 3.Drawthestructure
for
2-methyl-2-pentene

51. 4.Drawthestructure
for
2,3-dimethyl-1-
butene

53. 5. Name each compound
according to the IUPAC
system.

54. Uses/Application of
ALKENES

55. Thank you!