# Introduction to organic chemistry

> CIE A-Level Chemistry · CIE 9701
> Source: https://www.owlsprep.com/study/cie-9701-u12-overview/
> Weight: n/a

This unit lays the core vocabulary, naming rules, and foundational concepts required for all further study of organic chemistry in CIE A-Level Chemistry.

**Prerequisites:** [Basic understanding of covalent bonding and molecular shapes](https://www.owlsprep.com/study/cie-9701-u03-overview/)

## Learning objectives

- Name simple and branched organic compounds systematically following IUPAC rules
- Classify organic compounds by functional group and distinguish between types of isomerism
- Draw basic reaction mechanisms with correct curly arrow notation
- Relate carbon hybridization to the shape and bond angles of common organic molecules

## Unit at a glance

Organic chemistry is the study of carbon-based compounds, which form all living matter and most everyday synthetic materials. This unit establishes the common language all chemists use to describe organic molecules, so mastering the content here is critical for every organic topic that follows.

We progress from fundamental naming conventions, through classifying compounds and identifying isomers, to introducing the curly arrow notation used to explain how organic reactions occur, and finish by connecting bonding to the 3D shapes of organic molecules.

This unit includes the following core sub-topics:
- [Nomenclature](https://www.owlsprep.com/study/cie-9701-u12-nomenclature/) — Learn IUPAC rules for naming straight-chain, branched and simple cyclic organic compounds.
- [Functional groups and isomerism](https://www.owlsprep.com/study/cie-9701-u12-functional-groups-and-isomerism/) — Classify organic compounds by functional group and identify common types of structural and stereoisomerism.
- [Reaction mechanisms](https://www.owlsprep.com/study/cie-9701-u12-reaction-mechanisms/) — Master curly arrow notation to describe bond breaking and formation in basic organic reaction mechanisms.
- [Organic molecule shapes](https://www.owlsprep.com/study/cie-9701-u12-organic-molecule-shapes/) — Relate carbon hybridization to bond angles and 3D shapes of common organic functional groups.

## Common pitfalls

- **Wrong:** Numbering the carbon chain incorrectly for compounds with multiple functional groups
  - Why it fails: Higher priority functional groups must get the lowest possible carbon number, which is often overlooked
  - Correct: Always identify the highest priority functional group first before numbering the parent carbon chain
- **Wrong:** Drawing curly arrows starting from the wrong location
  - Why it fails: Curly arrows show movement of an electron pair, so they must start at the electron source
  - Correct: Start all curly arrows at a lone pair of electrons or an existing covalent bond
- **Wrong:** Confusing structural and stereoisomerism
  - Why it fails: Students often misclassify isomers by ignoring differences in atomic connectivity
  - Correct: If connectivity of atoms differs, it is structural isomerism; only differing spatial arrangement is stereoisomerism

## Cheatsheet

| Concept / Rule | Key Summary |
| --- | --- |
| IUPAC Naming Order | Identify parent chain → number to give highest priority group lowest number → name substituents alphabetically |
| Functional Group Priority Order | Carboxylic acids > esters > aldehydes > ketones > alcohols > alkenes > alkanes |
| Isomerism Types | Structural: chain, position, functional group; Stereoisomerism: cis-trans, optical |
| Curly Arrow Rule | Shows movement of an electron pair; starts at electron source, ends at electron destination |
| Bond Angles by Hybridization | $sp^3$ = 109.5°, $sp^2$ = 120°, $sp$ = 180° |
| Bond Fission Types | Homolytic: 1 electron to each atom → free radicals; Heterolytic: 2 electrons to one atom → ions |

## What's next

Begin your study of this unit with the first sub-topic on nomenclature to build your foundational naming skills. Once you complete all four sub-topics here, you will be ready to move on to the next unit covering hydrocarbons, where you will apply all the core concepts you learn in this unit.

- [Nomenclature](https://www.owlsprep.com/study/cie-9701-u12-nomenclature/)
- [Alkanes](https://www.owlsprep.com/study/cie-9701-u13-alkanes/)
- [Functional groups and isomerism](https://www.owlsprep.com/study/cie-9701-u12-functional-groups-and-isomerism/)

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