Chemistry 2: Organic Chemistry II (S.S.3 Class Note)

Core Concepts

Organic chemistry centers on how specific groups of atoms, known as functional groups, determine the chemical behavior of families of organic molecules.

1. Classification of Organic Compounds

We can classify organic compounds based on their functional groups:

• Alcohols (Alkanols): Contain the hydroxyl group ($-OH$). General formula: $C_nH_{2n+1}OH$.
• Carboxylic Acids (Alkanoic Acids): Contain the carboxyl group ($-COOH$). General formula: $C_nH_{2n+1}COOH$.
• Esters (Alkyloates): Contain the ester linkage ($-COO-$). Formed by reacting an alcohol with a carboxylic acid.
• Amines: Contain the amino group ($-NH_2$, $-NH-$, or $-N-$). They act as organic bases.

Figure 1: Ethanol, a primary alcohol showing the hydroxyl (-OH) functional group.

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2. Preparation and Properties of Ethanol

Ethanol ($C_2H_5OH$) is the most commercially significant alcohol. It is prepared via two main routes:

• Fermentation (Biological): Yeast enzymes (zymase) break down sugars (glucose) anaerobically at temperatures around 37 °C. $C_6H_{12}O_6 \xrightarrow{\text{zymase}} 2C_2H_5OH + 2CO_2$
• Hydration of Ethene (Industrial): Ethene is reacted with steam at high temperature (300 °C) and pressure (60 atm) using a phosphoric acid ($H_3PO_4$) catalyst. $C_2H_4 + H_2O \rightleftharpoons C_2H_5OH$

Key Chemical Reactions:

1. Combustion: Ethanol burns in excess oxygen with a clean blue flame, producing carbon dioxide and water. $C_2H_5OH + 3O_2 \rightarrow 2CO_2 + 3H_2O$
2. Oxidation: Acidified potassium dichromate(VI) ($K_2Cr_2O_7/H^+$) oxidizes ethanol first to ethanal, and then to ethanoic acid. The solution changes color from orange to green. $CH_3CH_2OH + [O] \rightarrow CH_3CHO + H_2O \xrightarrow{[O]} CH_3COOH$
3. Esterification: Ethanol reacts reversibly with ethanoic acid in the presence of concentrated sulfuric acid ($H_2SO_4$) catalyst to yield ethyl ethanoate (an ester) and water. $CH_3COOH + C_2H_5OH \rightleftharpoons CH_3COOC_2H_5 + H_2O$

Figure 2: The condensation reaction between a carboxylic acid and an alcohol to produce an ester.

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3. Polymerization

Polymerization is the process where small, repeating units called monomers chemically combine to form long-chain molecules called polymers.

• Addition Polymerization: Monomers containing carbon-carbon double bonds ($C=C$) join together without the loss of any small molecules.
  • Example: Ethene polymerizes to form Polyethene (polythene). $n(CH_2=CH_2) \rightarrow -[CH_2-CH_2]_n-$
• Condensation Polymerization: Monomers with two different functional groups combine, eliminating a small molecule (usually water or ammonia) as a byproduct.
  • Example: Nylon-6,6 and Terylene (synthetic), starch and proteins (natural).

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