Unsaturated Hydrocarbons - PowerPoint Presentation

Slide1

Unsaturated Hydrocarbons And Their Halogen Derivatives

IUG, Fall 2012

Dr

Tarek

ZaidaSlide2

Alkenes and Alkynes

1.

Alkenes

are compounds containing carbon –carbon double bonds

The simplest

alkene

,

ethene

, is a plant hormone.

Alkenes have physical properties similar to those of

alkanes

.

They are less dense than water and, being

nonpolar

, are not very soluble in water.

As with

alkanes

, compounds with four or fewer carbons are gases, whereas higher

homologs

are volatile liquids.Slide3

2. Alkynes,

compounds containing carbon–carbon triple bonds,

are similar to alkenes in their physical properties and chemical behavior.Slide4

General structural formula of Alkene and AlkynesSlide5

Both of these classes of hydrocarbons are unsaturated, because they contain fewer hydrogens

per carbon than

alkanes

(C

n

H

2n+2).

Alkanes

can be obtained from alkenes or alkynes by adding 1 or 2 moles of hydrogen.Slide6

What are all of the structural possibilities for the compound C3

H

4

?Slide7

Nomenclature

The IUPAC rules for naming alkenes and alkynes are similar to those for

alkanes

but a few rules must be added for naming and locating the multiple bonds.

1. The ending -

ene

is used to designate a carbon–carbon double bond. When more than one double bond is present, the ending is -

diene

, -

triene

, and so on. The ending -

yne

is used for a triple bond (-

diyne

for two triple bonds and so on). Compounds with a double and a triple bond are -

enynes

.

2. Select the longest chain that includes both carbons of the double or triple bond. Slide8

For example,Slide9

3. Number the chain from the end nearest the multiple bond so that the carbon atoms in that bond have the lowest possible numbers.

If the multiple bond is equidistant from both ends of the chain, number the chain from the

end nearest the first branch point

.Slide10

4. Indicate the position of the multiple bond using the lower numbered carbon atom of that bond. For example,

5. If more than one multiple bond is present, number the chain from the end nearest the first multiple bond.Slide11

If a double and a triple bond are equidistant from the end of the chain,

the double

bond receives the lowest numbers

. For example,Slide12
Slide13

The root of the name (eth- or prop-) tells us the number of carbons, and the ending (-ane

, -

ene

, or -

yne

) tells us whether the bonds are single, double, or triple. No number is necessary in these cases, because in each instance, only one structure is possible.

With four carbons, a number is necessary to locate the double or triple bond.Slide14

Branches are named in the usual waySlide15

CycloalkenesSlide16
Slide17

Reactions of Alkenes

1. Hydrogenation:

Slide18

Same with cycloalkenesSlide19

19

2. Addition

of Halogens to Alkenes

X

2

= Cl

2

and Br

2Slide20

Polymers

Large organic molecules formed from joining similar smaller molecules together.

The process is called polymerization.Slide21

Types of polymers

Naturally occurring:

Proteins,

Starch,

Cellulose

Rubber

Isoprene (present in natural rubber)

Slide22

2. Synthetic polymers:

Plastic

Nylon

Rayon (from cellulose)

Dacron (polyester)Slide23

Medical Uses of Polymers

Synthetic heart valves

Blood vessels

Surgical mesh

Disposable syringes

Drug containers Slide24
Slide25
Slide26
Slide27

Because rotation at carbon–carbon double bonds is restricted, cis

–trans isomerism

(geometric isomerism) is possible in appropriately substituted alkenes.

For example, 1,2-dichloroethene exists in two different forms:

Cis

–Trans IsomerismSlide28
Slide29

Cis-trans isomerism is possible for ring structure too:

Draw the structures of the cis-1,2-dimethylcyclopropane & trans-1,2-dimethylcyclopropaneSlide30

Cis-trans occurs in fatty acidsA biologically active cis

-trans isomer is

Cisplatin

, a chemotherapeutic agent used in the treatment of cancer.Slide31

Examples of biologically important Alkenes

Ethene

Linolenic

acid

Arachidonic

acid

β

-carotene

Vitamin A

Isoprene