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ORGANIC CHEMISTRY

K Warne

http://www.sciencecafe.org.za/









Distillation of Crude Oil










Homologous series

This is a series of compounds which all contain the same functional group, and have similar chemical properties.

ALKANES ALKENES ALCOHOLS

CH4 CH2 =CH2 CH3OH

CH3-CH3 CH2 =CH –CH3 CH3CH2OH

CH3-CH2-CH3 CH

2 =CH – CH

2 – CH

3

Each has a general formula:

ALKANES: CnH2n+2 ALKENES: CnH2n

ALCOHOLS: CnH2n+1OH

The members of the series differ by the number of CH2 units.

CH3-CH3, CH3-CH2-CH3, CH3-CH

2-CH

2-CH

3

Graduation in physical properties: eg: boiling points.

CH4 (GAS), C

8H

18 (LIQUID), C

30H

62 (SOLID)

As chains get longer Melting points increase (London forces get stronger)

as molecule surface area increases.










C C C C C C

C

C

H

H

H H

H H

H

H

H

H

H

H

H

H H

H

H

H

3-ethylhexane










Examples of Alkenes

ETHENE, C2H4 H H

C C

H H

OR CH2 CH2

PROPENE CH2 CH CH3

TASK: Use ball & stick models or sketches to construct and name 3 different structures for C4H8 each one with one double bond.

CH3CH2CH CH2

CH3CH CHCH3

CH3C CH2

CH3

BUT-1-ENE

BUT-2-ENE

METHYL PROPENE

H H

C C

H CH3










Functional groups

The functional groups are

………………. or

………………….. of atoms which determine the

……………………. of organic molecules.










STRUCTURES OF ALKANES

METHANE ……….

Bond Angle ……………. Shape ………………………

Can be illustrated as:








http://images.google.com/imgres?imgurl=www.dcu.ie/~chemist/pratt/cs204/perspect/methane.gif&imgrefurl=http://www.dcu.ie/~chemist/pratt/cs204/perspect/perspec1.htm&h=150&w=160&prev=/images%3Fq%3DMETHANE%26start%3D20%26svnum%3D10%26hl%3Den%26lr%3D%26ie%3DUTF-8%26sa%3DN

http://images.google.com/imgres?imgurl=www.purchon.com/chemistry/images/methane.gif&imgrefurl=http://www.purchon.com/chemistry/alkanes.htm&h=221&w=181&prev=/images%3Fq%3DMETHANE%26start%3D20%26svnum%3D10%26hl%3Den%26lr%3D%26ie%3DUTF-8%26sa%3DN

http://images.google.com/imgres?imgurl=members.tripod.com/~EppE/jpgs/methane.jpg&imgrefurl=http://members.tripod.com/~EppE/images.htm&h=425&w=594&prev=/images%3Fq%3DMETHANE%26svnum%3D10%26hl%3Den%26lr%3D%26ie%3DUTF-8%26sa%3DN



THE RULES FOR NAMING ORGANIC COMPOUNDS

1. Choose the longest unbroken chain of Carbon atoms and assign a name for the carbon chain using the prefixes; meth-1, eth-2 etc.

2. Identify any carbon chain branches (alkyl groups). These are assigned names using the same prefixes as above along with the suffix “-yl” – methyl, ethyl etc.

3. Identify the functional groups present in the molecule. Assign a prefix or suffix according to their homologous series. These will be written in front of the name of the carbon chain.

4. There is an order of precedence, to decide the suffix for the carbon chain:

COOH / C=C > OH > Br / Cl

5. Number the Carbon atoms in the longest chain so that the branches/functional groups have the lowest number possible. Allocate a number for every group/branch no matter how many times it occurs. Where groups are on the same carbon write their names in alphabetical order.

6. Numbering takes precedence "wins" over alphabetical spelling. Prefixes are used for groups that occur more than once.

Di – 2 Tri – 3 Tetra – 4 Penta – 5 etc.

7. The final name is written as one word with commas between numbers, hyphens separating numbers from words.










CH3–CH2–CH2–CH2Br PRIMARY 10

CH3–CH2–CH–CH3

Br

SECONDARY 20 …………………………….

TERTIARY 30

……………………………………………….. CH3 CH2–C–CH3

CH3

Br

………………………….










General formula ……………………………….

•CH3OH ………………… •CH3CH2OH ………………

•C3H7OH – two isomers

TASK: C4H9OH has 4 isomers. Draw the structures of each isomer giving the name and class of each one.










KNOWN AS ...................

STRUCTURE C O BOND ANGLE ..............

ALDEHYDES

GENERAL STRUCTURE

R

C O

H

EXAMPLES

HCHO - .............................

CH3CHO - ..................

CH3CH2CHO - ................

Illustrate the structures of these examples

















Carboxylic Acids

GENERAL FORMULA

EXAMPLES

HCOOH methanoic acid

CH3COOH ethanoic acid

CH3CH2COOH propanoic acid

Illustrate the structures of these examples. Name the anion formed in the acidic reaction.

Acidic reaction

CH3COOH + H2O CH3COO- + H3O+

R

C O

OH

Carboxyl group

-COOH












FORMATION OF ESTERS • GENERALLY: ACID + ALCOHOL ESTER + WATER catalysed by H+ ions normally from conc. H2SO4 O O R C + H O R/ R C + H2O OH O R/

O O H C + CH3OH H C + H2O OH O CH3 methanoic methanol methyl methanoate CH3CH2OH + CH3CH2COOH CH3CH2COOCH2CH3 + H2O










Physical Properties

Recognize and apply to particular examples the relationship between melting

points, boiling points, vapour pressure, viscosity and intermolecular forces

(hydrogen bonding, Van der Waals forces including dispersion or London

forces number and type of functional group, chain length, branched chains)

PHYSICAL PROPERIES

• vapour pressure

• melting points

• boiling points

• viscosity BONDING & STRUCTURE

• IMF

• Chain Length

• Branches

• Functional groups (no & type)

THESE

DEPEND ON THESE!










+ - + - + - + - + - + - + -

BONDING & STRUCTURE

• Chain Length – long chains increase IMF

CCCCCCC

H

H

HH

HH

HH

HH

HH

HH

H

H

CCCCCCC

H

H

HH

HH

HH

HH

HH

HH

H

H

Large surface area stronger van der waals forces (IMF)

CC C

C

C

H

H

HH

H

HH

H

H

H

H

H

CC C

C

C

H

H

HH

H

HH

H

H

H

H

H

Shorter or

branched chains

have less surface

area .: weaker IMF

• Branches – shorten chain – reduce IMF

Lots of dipoles

strong force!

+ -

+ -

+ -

+ -

Fewer dipoles

weak force!










Reaction Type Reaction

NAME (Type of type)

Applies to Forms Example Conditions/Notes

ADDITION

Halogenation Alkene/ynes Haloalkanes alkene + Br2 haloalkane X2 added to alkene

Hydrohalegenation Alkene/ynes Haloalkanes alkene + HBr haloalkane No Water present, H attatches to carbon with MOST H's

Hydration Alkene/ynes Alcohols alkenes + H2O alcohols XS H2O small amount of stron acid HX or H3PO4 H goes onto C with MOST H's

hydrogenation Alkene/ynes Alkanes alkenes + H2 alkanes alkene in N-polar solvent (Pt, Pd or Ni cat - atmosphere of H2)

SUBSTITUTION

Halogenation Alkanes Haloalkanes CH4 + Cl2 CH3Cl + HCL u.v light cataktst

Hydrolysis Haloalkanes Alcohols C2H5Br (EtOH) + NaOH(aq) + C2H5OH +

NaBr Ethanolic haloalkane, aq hydroxide, warm

halogenation Alcohols Haloalkanes CH3OH + H2504 + NaBr CH3Br + H2O primary & Secondary alcohols need c H2S04 + NaX, Tertiary room temp

ELIMINATION

Cracking Alkanes smaller alkanes + ethene heat and or catalyst

Dehydration Alcohols alkenes Alcohol --> alkene + H2O H removed from C

with least hydrogens (Gases heat Al2O3 cat) or liq cH2SO4 (or H3PO4)

Dehydrohalogenation

Haloalkanes ALkenes CH2Cℓ-CH2Cℓ → CH2 = CHCℓ + HCℓ Reflux, conc NaOH or KOH in ethanol (Hot ethanolic...)

Esterification Alcohols & carboxylic

acids Esters c acid + alcohol --> ester + H2O conc sulphuric acid + heat

COMBUSTION COMBUSTION All CO2 + H20 CH 50H + 302 --> 2C02+3H20 XS O2 complete --> CO2; insufficient O2 --> CO










Addition reactions • Unsaturated compounds undergo addition reactions to form saturated compounds e.g.

With any halogen (F2 Cl2 Br2 & I2)

CH2=CH2 + Cℓ2 CH2Cℓ-CH2Cℓ

With Br2 (aq) (brown liq) the decolourization is used as a test for alkenes

• hydrohalogentaion - addition of HX - halogenation - addition of X2 –

CH3CH=CH2 + HX CH3CHXCH3 (no water present)

• hydration - addition of H2O –

CH3CH=CH2 + H2O CH3CH OHCH3 (acid catalyst)

(The X-atom or OH-group attaches to the more substituted C-atom.)

• hydrogenation - addition of H2

CH3CH=CH2 + H2 CH3CH2CH3 (high temp Ni cat.)

(Used in the hardening of oils to make margarine)

(alkene dissolved in a non-polar solvent with catalyst (Pt, Pd or Ni) in an H2

atmosphere )










Elimination reactions • * Saturated compounds (haloalkanes, alcohols, alkanes) undergo

elimination reactions to form unsaturated compounds e.g.

CH2CℓCH2Cℓ CH2=CHCℓ + HCℓ

• - dehydrohalogentaion - elimination of HX from a haloalkane (alkene with

the more highly substituted double bond is the major product). –

CH3CH2CH2 X (hot )

• dehydration - elimination of H2O from an alcohol (alkene with the more

highly substituted double bond is the major product). –

CH3CH2CH2 OH ( conc )

• dehydrogenation - elimination of H2 from an alkane. -.

CH3CH2CH3

• cracking of alkanes

C16 H34 C9H20 + + 2 CH2=CH2 ( )

SAMPLE ONLY SAMPLE ONLY










Substitution reactions Reactions of HX with alcohols e.g.

ALCOHOL + HX HALOALKANE + WATER

(CH3)3OH + HBr →

• Reactions where the OH of alcohols are substituted with a halogen e.g.

HALOALKANE + KOH

(CH3)3Br + KOH →

• Two types of saturated structure can be inter-converted by substitution

as shown in the above two reaction equations.

ALCOHOL

HALOALKANE

• * Reactions of X2 with alkanes in the presence of light (prior

knowledge from Grade 11).

• Cl2 + CH4 SAMPLE ONLY SAMPLE ONLY










Substitution Conditions • Tertiary alcohols: HBr or HCl room temp

• Primary & Secondary: cH2SO4 solid NaBr/KBr

cH2SO4 + NaBr(s) HBr (+ Na2SO4)

Treat primary and secondary alcohols with concentrated H2SO4

and solid NaBr (or KBr). The H2SO4 and solid NaBr react to form

HBr: H2SO4 + NaBr → HBr + NaHSO4

The HBr reacts with the alcohol to form the bromoalkane:

e.g. CH3CH2OH + HBr → CH3CH2Br + H2O

SAMPLE ONLY SAMPLE ONLY










Hi -

This is a SAMPLE presentation only.

My FULL presentation, which contains loads more slides (100+) and other resources, are freely

available on my resource sharing website:

www.sciencecafe.org.za

(paste into your browser if link above does not work)

Have a look and enjoy!

Keith Warne










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