Chapter 4 Notes

The Chemistry of Carbon

Bonding Properties of Carbon

Carbon is a fundamental element in organic molecules due to its unique bonding properties. Its ability to form stable covalent bonds with a variety of elements makes it the backbone of biological macromolecules.

• Valence Electrons: Carbon has four valence electrons, allowing it to form up to four covalent bonds with other atoms.

• Common Bonding Partners: Carbon typically bonds with hydrogen, oxygen, nitrogen, sulfur, and phosphorus, as well as with other carbon atoms.

• Bond Types: Carbon can form single, double, or triple covalent bonds, resulting in a variety of molecular structures.

• Chain Formation: Carbon atoms can link together to form straight chains, branched chains, or rings.

Shapes, Angles, and Freedom of Carbon Bonds

• Tetrahedral Geometry: When carbon forms four single bonds, the resulting shape is a tetrahedron with bond angles of approximately 109.5°.

• Double and Triple Bonds: Double bonds create planar (flat) structures with bond angles of about 120°, while triple bonds result in linear arrangements with 180° angles.

• Rotation: Single bonds allow free rotation, but double and triple bonds restrict rotation, affecting molecular shape and function.

Example: Methane (CH4) is a classic example of a molecule with a tetrahedral geometry.

Isomers: Structural Diversity in Organic Molecules

Definition and Types of Isomers

Isomers are molecules with the same molecular formula but different structures or spatial arrangements, resulting in different properties.

• Structural Isomers: Differ in the covalent arrangement of their atoms. Example: Butane and isobutane (C4H10).

• Stereoisomers: Have the same covalent arrangement but differ in spatial orientation. Two main types are:

  • Cis-trans Isomers (Geometric Isomers): Differ in the arrangement of atoms around a double bond. Cis isomers have similar groups on the same side; trans isomers have them on opposite sides. Example: cis-2-butene vs. trans-2-butene.

  • Enantiomers: Are mirror images of each other and cannot be superimposed. They often have different biological activities. Example: L- and D- forms of amino acids or sugars.

Summary Table: Types of Isomers

Type	Definition	Example
Structural Isomers	Different covalent arrangements of atoms	Butane vs. isobutane
Cis-trans Isomers	Different spatial arrangement around double bonds	cis-2-butene vs. trans-2-butene
Enantiomers	Non-superimposable mirror images	L- and D- amino acids

Functional Groups in Organic Molecules

Definition and Importance

Functional groups are specific groups of atoms within molecules that have characteristic properties and chemical reactivity. Recognizing functional groups is essential for understanding the behavior of organic molecules in biological systems.

• Role: Functional groups determine the properties and reactions of organic molecules, including carbohydrates, lipids, proteins, and nucleic acids.

• Application: Knowledge of functional groups helps predict molecular behavior and interactions in biological processes.

Major Functional Groups in Biology

Functional Group	Structure	Properties	Example/Occurrence
Hydroxyl	-OH	Polar; forms hydrogen bonds	Alcohols (e.g., ethanol)
Carbonyl	>C=O	Polar; found in aldehydes and ketones	Acetone, formaldehyde
Carboxyl	-COOH	Weakly acidic; can donate H+	Organic acids (e.g., amino acids, fatty acids)
Amino	-NH2	Weakly basic; can accept H+	Amino acids
-SH	Forms disulfide bonds; stabilizes protein structure	Cysteine (an amino acid)
Phosphate	-PO42-	Weakly acidic; important in energy transfer	ATP, nucleic acids
Methyl	-CH3	Nonpolar; affects gene expression	Lipids, DNA methylation

Example: The carboxyl group (-COOH) in amino acids gives them acidic properties, while the amino group (-NH2) gives them basic properties, allowing amino acids to act as both acids and bases in biological systems.

Additional info: Understanding the chemistry of carbon and the diversity of functional groups is foundational for studying the structure and function of biological macromolecules.