Friday, September 2, 2022

CHEMISTRY FORM 5 ORGANIC CHEMISTRY -HALOGENATION AND HYDROGENATION

CHEMISTRY FORM 5 ORGANIC CHEMISTRY -HALOGENATION AND HYDROGENATION

CHEMISTRY FORM 5 ORGANIC CHEMISTRY -HALOGENATION AND HYDROGENATION
Friday, September 2, 2022

CHEMISTRY FORM 5 ORGANIC CHEMISTRY -HALOGENATION AND HYDROGENATION

UNAWEZA JIPATIA NOTES ZETU KWA KUCHANGIA KIASI KIDOGO KABISA:PIGA SIMU:0787237719




ALSO READ;

  1. O’ Level Study Notes All Subjects
  2. A’ Level Study Notes All Subjects
  3. Pats Papers

ORGANIC CHEMISTRY -HALOGENATION AND HYDROGENATION

Halogenation

D:\..\..\thlb\cr\tz\organic1_files\image014.png Addition of halogens to alkenes

–          This reaction is best carried out by simply mixing halogens in the inert solvents such as carbon tetrachloride (CCl4)
D:\..\..\thlb\cr\tz\__i__images__i__\z9.jpg

E.g.

D:\..\..\thlb\cr\tz\__i__images__i__\bn1.jpg

The reaction of Bromine with alkene can be used to test for the presence of double bonds.

Reason:

Addition of bromine (brown) to alkene since it makes the solution colourless. This is how we test for presence of double bonds.

Bromine tests unsaturation of hydrocarbons (alkenes and alkynes).




4. HYDROGENATION

Addition of hydrogen:

–          Alkenes react with hydrogen in the presence of platinum or nickel catalyst to form alkanes.

D:\..\..\thlb\cr\tz\__i__images__i__\h43.png

  This cannot take place without catalyst.

5. Hydration of Alkenes:

–          This follows Markrnkov’s rule.

Homework on hydration of alkenes

–          Find the reagent which should be added to alkene to follow Anti markornikovs rule.

Oxidation reaction of alkenes

6. Addition of Bromine water (Br2/H2O)

       D:\..\..\thlb\cr\tz\__i__images__i__\j_7.PNG

D:\..\..\thlb\cr\tz\__i__images__i__\BJ.jpg

D:\..\..\thlb\cr\tz\__i__images__i__\BM1.jpg

Alkenes decolourize Bromine water (Brown) apart from decolorizing Bromine solution.

Reaction with conc H2 SO4

Structure of sulphuric acid

D:\..\..\thlb\cr\tz\__i__images__i__\IO.jpg

D:\..\..\thlb\cr\tz\__i__images__i__\uio.png

ORGANIC CHEMISTRY -HALOGENATION AND HYDROGENATION

7. Oxidation reactions of Alkenes

–                     Alkenes react with oxidizing agent to form diols. Oxidizing agent can be either KMnO4, K2CrO4.

 

–          With cold dilute KMnO4 or cold alkalineKMnO4 you form diols.

D:\..\..\thlb\cr\tz\__i__images__i__\j_8.PNG

 

NOTE: Diol means two OH

D:\..\..\thlb\cr\tz\__i__images__i__\a65.jpg

(b) When hot concentrated acidified KMnO4 or K2Cr2O4 is used. Alkenes are oxidized to carboxylic acid or oxidized to ketones or both.

D:\..\..\thlb\cr\tz\__i__images__i__\b17.jpg

 

Note:

If double bond is branched, you can’t form carboxylic acid.

Terminal alkene

D:\..\..\thlb\cr\tz\__i__images__i__\J8.jpg

OZONOLYSIS (O3)Ozono  D:\..\..\thlb\cr\tz\organic1_files\image014.png    ozone

Lysis    D:\..\..\thlb\cr\tz\organic1_files\image014.png   Breaking

–          This is a cleavage or breaking of carbon, carbon double bond by using ozone.

–          In ozonolysis C = C is completely broken to produce aldehydes or ketones or both depending on the primary structure of alkene.





NOTE:

Ozonolysis is the best method of locating the position of double bond in unknown alkene.

The oxygenated carbon in carbonyl compound obtained by ozonolysis is the one that were joined by double bonds in the original alkenes.

Ozonolysis has 2 major steps:

i)                    1st step:

D:\..\..\thlb\cr\tz\__i__images__i__\BN1.PNG

NOTE:

Zn dust is added to prevent oxidation of aldehyde to carboxylic acid.

E.g.

D:\..\..\thlb\cr\tz\__i__images__i__\D30.jpg D:\..\..\thlb\cr\tz\__i__images__i__\E25.jpg

 

Questions

1.     A certain compound A was unsaturated hydrocarbon with molecular formula C6 H12. During ozonolysis of A, two compounds C and D were formed with molecular formula C3H6O. Compound C and compound D was ketone. Identify A, C and D.

 

Solution:

D:\..\..\thlb\cr\tz\__i__images__i__\f64.jpg

D:\..\..\thlb\cr\tz\__i__images__i__\hh9.png
D:\..\..\thlb\cr\tz\__i__images__i__\H20.jpg



CHEMISTRY FORM 5 ORGANIC CHEMISTRY -HALOGENATION AND HYDROGENATION
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