Chapter 4: Carbon, Bonds, and Functional Groups – Study Notes

Chapter 4: Carbon, Bonds, and Functional Groups

Objectives

• Explain the importance of carbon in biological molecules.

• Understand and apply the concept of isomers.

• Identify and describe various functional groups found in organic molecules.

Review of Chemical Bonds

Covalent Bonds and Molecules

Atoms combine to form molecules through chemical bonds. The most important type of bond in biological molecules is the covalent bond, which involves the sharing of electrons between atoms.

• Covalent bonds can result in polar or non-polar molecules, depending on the electronegativity difference between the atoms involved.

• Polar molecules have unequal sharing of electrons, leading to partial charges, while non-polar molecules have equal sharing.

Carbon and the Molecular Diversity of Life

Importance of Carbon

Organic chemistry is the study of carbon compounds. Carbon is central to the chemistry of life because of its unique bonding properties.

• Almost all molecules associated with life contain carbon.

• A carbon atom has a valence of 4, allowing it to form up to four covalent bonds with other atoms.

• The electronegativity of carbon allows it to form both polar and non-polar bonds, contributing to molecular diversity.

• Carbon-based molecules can be reduced or oxidized, storing or releasing energy as needed for biological processes.

• Major classes of biological macromolecules—proteins, nucleic acids, carbohydrates, and lipids—are all built on carbon skeletons.

Hydrocarbons

Structure and Types of Hydrocarbons

Hydrocarbons are organic molecules consisting entirely of carbon and hydrogen. Their structure can vary in several ways, leading to molecular diversity.

• Length: Hydrocarbons can have different numbers of carbon atoms (e.g., ethane, propane).

• Branching: The carbon chain can be straight or branched (e.g., butane vs. isobutane).

• Double Bond Position: Double bonds can occur at different positions (e.g., 1-butene vs. 2-butene).

• Presence of Rings: Some hydrocarbons form ring structures (e.g., cyclohexane, benzene).

Isomers

Types of Isomers

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

• Structural isomers: Differ in the covalent arrangement of their atoms.

• Geometric isomers (cis-trans isomers): Differ in spatial arrangement around a double bond (C=C). For example, cis-2-butene and trans-2-butene.

• Enantiomers: Are mirror images of each other and cannot be superimposed. They are built around an asymmetric (chiral) carbon atom.

Example: L- and D- forms of amino acids are enantiomers; only L-amino acids are used in proteins.

Functional Groups

Definition and Importance

Functional groups are specific groups of atoms attached to the carbon skeleton of organic molecules. They are the components most commonly involved in chemical reactions and largely determine the properties and reactivity of molecules.

• The number and arrangement of functional groups give each molecule its unique properties.

• Functional groups are key to the function of biological molecules such as hormones (e.g., estradiol and testosterone differ only in their functional groups).

Major Functional Groups in Biology

Functional Group	Structure	Properties	Example
Hydroxyl	-OH	Polar, forms hydrogen bonds, increases solubility in water	Alcohols (e.g., ethanol)
Carbonyl	C=O	Polar; found in sugars as either aldehydes (at end of chain) or ketones (within chain)	Aldehyde: propanal; Ketone: acetone
Carboxyl	-COOH	Acts as an acid (can donate H+); found in amino acids and fatty acids	Acetic acid
Amino	-NH2	Acts as a base (can accept H+); found in amino acids	Glycine
Sulfhydryl	-SH	Forms disulfide bonds, important for protein stabilization	Cysteine (an amino acid)
Phosphate	-PO42-	Contributes negative charge, can transfer energy (as in ATP), very reactive	ATP, DNA backbone

Summary Table: Functional Groups

Name	Formula	Properties	Example
Hydroxyl	-OH	Polar, forms hydrogen bonds	Alcohols
Carbonyl	C=O	Polar, found in sugars	Aldehydes, Ketones
Carboxyl	-COOH	Acidic, donates H+	Carboxylic acids
Amino	-NH2	Basic, accepts H+	Amines
Sulfhydryl	-SH	Forms disulfide bonds	Thiols
Phosphate	-PO42-	Negative charge, energy transfer	Organic phosphates

Key Equations and Concepts

• Valence of Carbon: $\text{Valence of C} = 4$

• General formula for hydrocarbons: $C_nH_{2n+2}$ (alkanes)

• Isomerism: Isomers have the same molecular formula but different structures and properties.

Examples and Applications

• Estradiol vs. Testosterone: These hormones have the same carbon skeleton but differ in functional groups, leading to different biological effects.

• ATP (Adenosine Triphosphate): Contains phosphate groups that store and transfer energy in cells.

Additional info: The notes have been expanded to include definitions, examples, and a summary table for clarity and completeness, as would be expected in a mini-textbook study guide.