【Chemistry】Welcome to the World of Organic Compounds!

Hello! Let's start learning about "organic compounds" together. You might feel like "chemistry seems so difficult..." but in reality, almost everything around us (food, clothes, plastic, and even our own bodies!) is made of organic compounds.
In this chapter, we will carefully unravel the secrets of these essential substances, starting from the basics. Think of it like putting together a puzzle—have fun with it!

1. What are Organic Compounds?

First, let’s define what an "organic compound" is. In short, it is a compound that is centered around carbon (C) atoms.

Carbon (C) is the "King of Bonding"

A carbon atom has 4 "hands" (valence electrons) to hold hands with other atoms. By using these 4 "hands," carbon atoms can connect in long chains, form branches, or create rings, allowing them to form an almost infinite variety of substances.

【Point: Exceptions to Organic Compounds】 Even though they contain carbon, substances like carbon monoxide (\(CO\)), carbon dioxide (\(CO_2\)), and calcium carbonate (\(CaCO_3\)) are classified as "inorganic substances" because their properties are different. Just keep that in mind!

2. Classification of Hydrocarbons (The Basics)

Compounds made only of carbon (\(C\)) and hydrogen (\(H\)) are called hydrocarbons. These are the most fundamental building blocks of organic compounds. Their names change based on how they bond.

① Alkanes (All single bonds)

This group consists of chains where carbon atoms are connected by only one line (single bonds). General formula: \( C_nH_{2n+2} \)
Examples: Methane (\(CH_4\)), ethane (\(C_2H_6\)), propane (\(C_3H_8\))

② Alkenes (Contain one double bond)

This group features a chain where there is exactly one place with two lines (a double bond) between carbons. General formula: \( C_nH_{2n} \)
Examples: Ethylene (\(C_2H_4\)), propene (\(C_3H_6\))

③ Alkynes (Contain one triple bond)

This group features a chain where there is exactly one place with three lines (a triple bond) between carbons. General formula: \( C_nH_{2n-2} \)
Examples: Acetylene (ethyne) (\(C_2H_2\))

【Did you know?】 Alkanes are called saturated hydrocarbons because they are "full" and cannot bond with any more hydrogen! Conversely, alkenes and alkynes, which have double or triple bonds, are called unsaturated hydrocarbons because they still have "room" to accept more hydrogen.

Summary of this section:

Carbon has 4 "hands"! First, try to memorize the names and general formulas for alkanes, alkenes, and alkynes as a set!

3. "Functional Groups": The Key to Chemical Personality

The properties of an organic compound (such as how easily it reacts or how well it dissolves) are determined by specific "components" attached to the carbon chain. These components are called functional groups.

Let's look at some representative functional groups:

  • Hydroxy group (\(-OH\)): Compounds with this are called alcohols. It’s a "magic" component that makes a substance easier to dissolve in water.
  • Ether linkage (\(-O-\)): This is where an oxygen atom acts as a bridge between two carbons. These are called ethers.
  • Aldehyde group (\(-CHO\)): Characterized by having reducing properties (the power to reduce other substances).
  • Carboxy group (\(-COOH\)): Compounds with this are called carboxylic acids (like acetic acid) and show acidic properties.

【Study Tip】 You might think, "The names are so similar, it's confusing!" at first. For example, since the component in alcohol is ethyl alcohol (ethanol), it’s easy to remember the hydroxy group by thinking of it as a "relative of alcohol."

4. Structural Isomers: Same Ingredients, Different Shape?

An interesting (and sometimes tricky) part of organic chemistry is the "structural isomer."

These are substances that have the same molecular formula (number of atoms) but a different connection (structure). If you compare it to building blocks, even if you have "4 blue parts and 2 red parts," you can build either a "car" or an "airplane" depending on how you put them together.

【Common Mistake】 Things that are just "rotated" in space are not isomers! Even if they look different when you draw them on paper, if the sequence of "what is connected to what" is the same, they are the same substance.

Summary of this section:

Even if the ingredients are the same, if the way they are connected is different, the name and properties of the substance will be completely different!

5. Steps to Master Organic Compounds

If you aren't sure where to start, try moving through these steps:

  1. Always keep in mind that carbon has 4 "hands." (When drawing structural formulas, check that you don't have more or less than 4 connections per carbon!)
  2. Memorize the names like a chant: "Methane, ethane, propane, butane..." (The names for 1–4 carbons are the foundation.)
  3. Match the names of functional groups to their shapes. (Starting with \(-OH\) and \(-COOH\) is perfectly fine!)

You don't need to be perfect from the start! Like fitting puzzle pieces together one by one, enjoy the feeling of the names and shapes gradually making sense. I’m rooting for you!

【Final Advice】 Drawing structural formulas yourself is the fastest way to learn. Grab some scrap paper, draw carbon chains, and practice attaching hydrogen to them!