Chapter 3: Big Ideas – Introduction to Organic Compounds

Introduction to Organic Compounds

Overview

Organic compounds are the foundation of life’s molecular diversity. Their unique properties arise from the structure and bonding capabilities of carbon atoms, which form the backbone of most biological molecules.

• Organic compounds are molecules primarily composed of carbon atoms bonded with other elements, especially hydrogen, oxygen, and nitrogen.

• Life’s molecular diversity is based on the versatility of carbon.

Life’s Molecular Diversity and the Properties of Carbon

Carbon’s Bonding and Structural Diversity

Carbon atoms can form four covalent bonds, allowing for a wide variety of stable and complex molecules.

• Carbon chains form the backbone of most organic molecules.

• Isomers are compounds with the same molecular formula but different structures, resulting in different properties.

• Hydrocarbons are composed only of carbon and hydrogen atoms.

Examples of Carbon Skeletons

• Chains: Vary in length (e.g., methane, ethane, propane).

• Double bonds: Carbon skeletons may have double bonds, which can vary in location (e.g., 1-butene, 2-butene).

• Branching: Skeletons can be unbranched (butane) or branched (isobutane).

• Rings: Carbon skeletons may form rings (e.g., cyclohexane, benzene).

Example: Benzene (C6H6) is a ring structure with alternating double bonds, important in many biological molecules.

Chemical Groups and Biological Function

Functional Groups

The properties of organic molecules are influenced by the presence of specific groups of atoms called functional groups. These groups confer specific chemical properties and reactivity to the molecules.

• Functional groups are often hydrophilic, increasing the solubility of organic compounds in water.

• Six important functional groups are commonly found in biological molecules.

Example: The difference between the sex hormones testosterone and estradiol is due to the presence of different functional groups attached to a common carbon skeleton.

Table: Major Functional Groups in Organic Compounds

Functional Group	Structure	Example	Properties
Hydroxyl	–OH	Alcohols (e.g., ethanol)	Polar, forms hydrogen bonds
Carbonyl	–C=O	Aldehydes, ketones	Polar, found in sugars
Carboxyl	–COOH	Carboxylic acids (e.g., acetic acid)	Acidic, donates H+
Amino	–NH2	Amines (e.g., glycine)	Basic, accepts H+
Phosphate	–OPO32–	Organic phosphates (e.g., ATP)	Contributes negative charge, energy transfer
Methyl	–CH3	Methylated compounds	Nonpolar, affects gene expression

Additional info: Functional groups are key to the reactivity and interaction of biomolecules, influencing processes such as enzyme activity and cell signaling.