What is a Functional Group?

• Definition: A functional group is a specific grouping of atoms within a molecule that exhibits characteristic properties, regardless of the other atoms present.
• Importance: Functional groups are key to understanding organic chemistry because they dictate how molecules behave in reactions.
• Examples: Common functional groups include alcohols, alkenes, alkynes, amines, carboxylic acids, aldehydes, ketones, esters, and ethers.

Hydrocarbons

• A. Alkanes

  • Definition: Hydrocarbons containing only single bonds between carbon atoms.
  • Properties: Non-polar, very weak acids, low boiling points, generally unreactive (except for combustion and free-radical substitution).
  • Examples: Methane, ethane, propane.
  • Nomenclature: End with “-ane” (e.g., propane).

• B. Alkenes

  • Definition: Hydrocarbons with at least one carbon-carbon double bond.
  • Properties: More reactive than alkanes due to the double bond.
  • Examples: Ethene, propene.
  • Nomenclature: End with “-ene” (e.g., propene).
  • Geometric Isomers: Possible due to restricted rotation around the double bond (cis/trans or E/Z isomers).

• C. Alkynes

  • Definition: Hydrocarbons with at least one carbon-carbon triple bond.
  • Properties: Even more reactive than alkenes.
  • Examples: Ethyne (acetylene).
  • Nomenclature: End with “-yne” (e.g., propyne).

• D. Aromatic Rings

  • Definition: Six-membered rings with alternating double bonds, often represented as a hexagon with a circle inside.
  • Properties: Unusually stable due to aromaticity.
  • Examples: Benzene, toluene.
  • Nomenclature: Often named as derivatives of benzene (e.g., methylbenzene).

Functional Groups Containing Oxygen

• A. Alcohols

  • Definition: Contain the hydroxyl group (-OH) bonded to a carbon atom.
  • Properties: Polar, capable of hydrogen bonding, higher boiling points than alkanes, weak acids.
  • Classification: Primary, secondary, or tertiary, depending on the carbon the -OH group is attached to.
  • Examples: Methanol, ethanol, isopropanol.
  • Nomenclature: End with “-ol” (e.g., ethanol).

• B. Ethers

  • Definition: Oxygen atom singly bonded to two carbon atoms (R-O-R).
  • Properties: Relatively unreactive, good solvents for nonpolar molecules.
  • Examples: Diethyl ether, tetrahydrofuran.
  • Nomenclature: Name the two alkyl groups attached to the oxygen followed by “ether” (e.g., diethyl ether).

• C. Aldehydes

  • Definition: Carbonyl group (C=O) bonded to at least one hydrogen atom (RCHO).
  • Properties: Polar, reactive due to the carbonyl group, can be oxidized to carboxylic acids and reduced to primary alcohols.
  • Examples: Formaldehyde, acetaldehyde.
  • Nomenclature: End with “-al” (e.g., propanal).

• D. Ketones

  • Definition: Carbonyl group (C=O) bonded to two carbon atoms (RCOR).
  • Properties: Polar, less reactive than aldehydes.
  • Examples: Acetone.
  • Nomenclature: End with “-one” (e.g., propanone).

• E. Carboxylic Acids

  • Definition: Carbonyl group (C=O) bonded to a hydroxyl group (RCOOH).
  • Properties: Weak acids, capable of hydrogen bonding, higher boiling points than corresponding aldehydes or ketones.
  • Examples: Formic acid, acetic acid.
  • Nomenclature: End with “-oic acid” (e.g., propanoic acid).

• F. Esters

  • Definition: Similar to carboxylic acids but with an -OR group instead of -OH (RCOOR’).
  • Properties: Often have pleasant odors.
  • Formation: From the reaction of a carboxylic acid with an alcohol.
  • Nomenclature: Name the alkyl group attached to the oxygen followed by the parent carboxylic acid name with “-ate” replacing “-ic acid” (e.g., methyl propanoate).

Functional Groups Containing Nitrogen

• A. Amines

  • Definition: Nitrogen atom bonded to one or more carbon atoms.
  • Properties: Basic, capable of hydrogen bonding (primary and secondary amines), often have strong odors.
  • Classification: Primary, secondary, or tertiary, depending on the number of carbons bonded to the nitrogen.
  • Examples: Methylamine, dimethylamine, trimethylamine.
  • Nomenclature: End with “-amine” (e.g., methylamine) or use “-amino” as a prefix in more complex molecules.

• B. Amides

  • Definition: Carbonyl group (C=O) bonded to a nitrogen atom (RCONH2).
  • Properties: Polar, less basic than amines due to resonance.
  • Formation: From the reaction of a carboxylic acid with ammonia or an amine.
  • Nomenclature: End with “-amide” (e.g., propanamide).

• C. Nitriles

  • Definition: Carbon triple-bonded to a nitrogen atom (RCN).
  • Properties: Polar.
  • Nomenclature: End with “-nitrile” (e.g., propanenitrile) or use “cyanide” as a suffix with the alkyl group (e.g., ethyl cyanide).

Alkyl Halides

• Definition: Alkanes with one or more hydrogen atoms replaced by halogen atoms (F, Cl, Br, I).
• Properties: Polar, often used in substitution and elimination reactions.
• Examples: Chloromethane, bromobutane.
• Nomenclature: Name the halogen as a prefix to the alkane name (e.g., chloromethane).

Key Concepts

• Bond Dissociation Energy: The energy required to break a bond homolytically (each atom gets one electron). Important for understanding radical reactions.
• Transition State: A high-energy, unstable state that a reaction must pass through to form products. Not isolable.
• Carbocations: Positively charged carbon atoms. Important intermediates in many organic reactions, especially SN1 and E1 reactions.
• Reaction Mechanisms: Step-by-step descriptions of bond breaking and bond forming in a chemical reaction. Crucial for understanding why reactions occur and predicting products.

References

1. Smith, J. (2010). Functional Groups in Organic Chemistry. Master Organic Chemistry. Retrieved from https://www.masterorganicchemistry.com/2010/10/06/functional-groups-organic-chemistry/

2. Florida State University. (n.d.). Functional Groups. Retrieved from https://www.chem.fsu.edu/chemlab/chm1046course/functional.html

3. Soult, A. (n.d.). Functional Groups. In Chemistry for Allied Health (CHE 103). University of Kentucky. Retrieved from https://chem.libretexts.org/Courses/University_of_Kentucky/CHE_103%3A_Chemistry_for_Allied_Health_(Soult)/04%3A_Structure_and_Function/4.04%3A_Functional_Groups

4. Encyclopaedia Britannica. (n.d.). Functional Groups. In Chemical Compound. Retrieved from https://www.britannica.com/science/chemical-compound/Functional-groups