Overview
This lecture introduces major functional groups attached to hydrocarbon backbones, highlighting their chemical properties and biological significance.
Introduction to Functional Groups
- Functional groups are specific atoms or groups of atoms added to hydrocarbons to alter molecular properties and reactivity.
- Functional groups make hydrocarbons more interesting chemically and biologically.
Hydroxyl and Sulfhydryl Groups
- A hydroxyl group (–OH) attached to a carbon backbone defines an alcohol, such as ethanol.
- Hydroxyl groups are polar and hydrophilic due to highly electronegative oxygen, allowing hydrogen bonding and water solubility.
- A sulfhydryl group (–SH) is similar to hydroxyl but contains sulfur, which is less electronegative than oxygen, making it less polar.
- Both groups can be represented using the "R" notation for the carbon backbone.
Carbonyl and Carboxyl Groups
- Carbonyl group (C=O) consists of a carbon double-bonded to oxygen; present in sugars and makes the molecule polar.
- In straight-chain sugars like fructose, carbonyl and multiple hydroxyl groups contribute to high polarity.
- The carbon in a carbonyl group is electrophilic and susceptible to nucleophilic attack.
- A carboxyl group (–COOH) is a carbonyl bonded to a hydroxyl; it behaves as an acid because it can easily donate a hydrogen proton.
Amino and Methyl Groups
- Amino groups (–NH₂) contain nitrogen and are basic as they can pick up hydrogen ions (protons).
- Amino acids feature both carboxyl (acidic) and amino (basic) groups attached to a carbon chain.
- Methyl groups (–CH₃) are simple hydrocarbon groups, non-polar, and hydrophobic.
Phosphate Groups
- Phosphate groups (–PO₄H₂) are found in biological molecules like ATP and DNA.
- When protonated, phosphate groups are acidic as they can donate protons to the solution.
Key Terms & Definitions
- Functional Group — a specific group of atoms attached to a molecule, determining its properties.
- Hydroxyl Group (–OH) — confers polarity and hydrophilicity; defines alcohols.
- Sulfhydryl Group (–SH) — similar to hydroxyl, but less polar; found in some amino acids.
- Carbonyl Group (C=O) — carbon double bonded to oxygen; increases polarity, reactive site in sugars.
- Carboxyl Group (–COOH) — carbonyl plus hydroxyl; acidic, easily donates a proton.
- Amino Group (–NH₂) — nitrogen-containing, basic; accepts protons.
- Methyl Group (–CH₃) — non-polar hydrocarbon group; hydrophobic.
- Phosphate Group (–PO₄H₂) — acidic, important in energy transfer and nucleic acids.
Action Items / Next Steps
- Review the structures and properties of each functional group.
- Be able to identify functional groups in complex biological molecules.
- Prepare for exercises on predicting molecule solubility and reactivity based on functional groups.