12.7. Properties and Reactions of Organic Compounds

● Combustion: Organic compounds burn in air to produce CO₂ and H₂O. ○ CH₄ + 2O₂ → CO₂ + 2H₂O

Combustion is a chemical reaction in which organic compounds react with oxygen to produce carbon dioxide (CO₂) and water (H₂O). For example, when methane (CH₄), a common organic compound found in natural gas, burns in the presence of oxygen (O₂), it produces carbon dioxide and water. The reaction can be summarized as CH₄ + 2O₂ → CO₂ + 2H₂O.

Think of combustion as how a campfire works. When you add wood (which is made of organic compounds) to the fire, it combines with oxygen in the air and burns, producing smoke (which contains carbon dioxide) and steam (water vapor). This is how we get warmth and light from the fire.

● Substitution Reactions (in alkanes): One atom replaces another.

Substitution reactions are a type of chemical reaction where one atom or a group of atoms in a molecule is replaced by another atom or group of atoms. This type of reaction commonly occurs in alkanes, which are saturated hydrocarbons. For example, when chlorine reacts with methane in the presence of ultraviolet light, one of the hydrogen atoms in methane can be replaced by a chlorine atom, resulting in chloromethane.

You can think of a substitution reaction as replacing a player on a sports team. If one player is substituted for another, the team remains the same in essence but changes in composition. Similarly, in a substitution reaction, the overall structure of the molecule stays the same, but one part has changed.

● Addition Reactions (in alkenes/alkynes): Atoms add to unsaturated bonds.

Addition reactions occur in unsaturated hydrocarbons, such as alkenes and alkynes, where atoms or groups of atoms are added to the double or triple bonds. For instance, when ethene (an alkene with a double bond) reacts with hydrogen gas, the double bond opens up, and hydrogen atoms are added, producing ethane.

Imagine a door that can only open halfway (like the double bond in alkenes). When you add a second person to the doorway (like adding hydrogen), the door can fully open, allowing both people to pass through (the addition of hydrogen to create ethane). This represents the addition of atoms in the reaction.

● Oxidation: Alcohols → Acids using oxidizing agents.

Oxidation is a chemical reaction where a substance loses electrons or increases its oxidation state. In organic chemistry, alcohols can be oxidized to form acids. This typically requires the use of an oxidizing agent such as potassium dichromate. For example, ethyl alcohol (ethanol) can be oxidized to acetic acid when treated with an oxidizing agent.

You can compare the oxidation of alcohols to how a piece of ripe fruit can spoil. When fruits are fresh, they are sweet (like alcohols). Over time, when they oxidize, they might turn sour and ferment (like becoming acids). This transformation illustrates how alcohols convert into acids through oxidation.

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