Organic

• Organic compounds are classified into different homologous series such as alkenes, alkanes, alcohols, carboxylic acids, ketones, aldehydes, phenols
• Each member of a homologous series contains the same relative group of atoms called the functional group
• Some organic compounds have two or more functional groups
• Physical properties of organic compounds:

  • Have a molecular structure
  • Weak Van der Waals forces between molecules in liquid and solid states
  • Most are insoluble in water, but some can form hydrogen bonds and are soluble
  • Higher boiling points due to hydrogen bonds between molecules
• Boiling points:

  • Ethanol (C2H5OH) has a boiling point of 78°C
  • Propane (C3H8) has a boiling point of -48°C
  • Ethanol has a higher boiling point than propane due to hydrogen bonds between molecules
• Solubility:

  • Solubility decreases as the size of the hydrophobic group increases
  • Hydrophobic groups include C-H and benzene rings
  • Hydrophilic groups form hydrogen bonds and increase solubility
• Definitions:

  • Molecular formula: shows actual numbers of each type of atoms in a molecule
  • Structural formula: shows how atoms or groups are bonded in the molecule
  • Displayed formula: drawing showing all atoms and bonds in a molecule
  • Skeletal formula: simplified version of displayed formula
  • Structural isomers: compounds with the same formula but different structures
  • Geometrical isomers: same formula and structure but different spatial arrangements
  • Optical isomers: same formula, structure, and arrangement but differ in light rotation direction
• Factors affecting properties of organic compounds:

  • Number and arrangement of carbon atoms
  • Functional groups in the molecule
• Functional groups:

  • Alkane: C-C and C-H single bonds only
  • Alkene: C=C double bond
  • Haloalkane: Cl, Br, or I atom attached to a carbon atom
• Ways to represent organic compounds:

  • Structural formula showing all covalent bonds
  • Structural formula not showing all covalent bonds
  • Molecular formula
  • Empirical formula
• Homologous series:

  • Organic compounds with the same functional group but different carbon atoms belong to the same series
  • Formula of each successive member increases by -CH2-
  • As series ascends, size of molecules increases, leading to stronger Van der Waal’s forces and higher boiling points
• Nomenclature of organic compounds:

  • Longest straight carbon chain
  • Nature and position of functional groups
  • Alkanes named with -ane ending
  • Alkenes named with -ene ending, position of double bond specified
  • Halogenoalkanes named with chloro-, bromo-, or iodo- prefixes
• Branches on molecules:

  • Methyl and ethyl prefixes for branches
  • Position of branch specified by numbering carbons on straight chain
  • Different notations may represent the same compound
• Nomenclature of compounds with multiple functional groups:

  • Naming based on prefixes and endings for different functional groups
  • Different naming conventions for alcohols with other functional groups
• Isomerism:

  • Compounds with the same molecular formula but different structures
  • Types include structural isomerism and stereoisomerism
• Isomerism can be divided into two types: structural isomerism and stereoisomerism
• Structural isomerism can be further subdivided into three types: positional isomerism, chain isomerism, and functional isomerism
• Stereoisomerism has two types: geometrical isomerism and optical isomerism
• Chain isomerism is a type of structural isomer where molecules have the same molecular formula but different arrangement of carbon atoms
• For chain isomerism, a minimum of 4 carbons should be present in the molecule
• Positional isomerism occurs in molecules with the same molecular formula but different positions of the functional group
• Functional group isomers are molecules with the same molecular formula but different functional groups
• Chiral molecules cannot be superimposed on their mirror image and are called optical isomers or enantiomers
• Molecules with at least one carbon atom attached to four different groups exhibit optical isomerism
• Optical isomers show identical chemical properties in most reactions, but certain biochemical processes require specific orientations of groups
• Different optical isomers may have very different biochemical effects
• Types of reactions in organic chemistry include: substitution, addition, elimination, rearrangement, and oxidation reactions
• Primary alcohols can be oxidised to either aldehydes or carboxylic acids depending on the reaction conditions
• Partial oxidation of primary alcohols results in aldehydes, while full oxidation leads to carboxylic acids
• Full oxidation to carboxylic acids requires using an excess of the oxidising agent and ensuring that the aldehyde formed as the half-way product stays in the mixture
• Primary alcohols can be fully oxidised to carboxylic acids by heating under reflux with acidified potassium permanganate, which does not produce aldehydes
• Secondary alcohols are oxidised to ketones, for example, propan-2-ol with sodium or potassium dichromate (VI) solution acidified with dilute sulphuric acid produces propanone
• Tertiary alcohols are not oxidised by acidified sodium or potassium dichromate (VI) solution
• Electronegativities: C=2.5, H=2.1, O=3.5, F=4.0, Cl=3.0, Br=2.8, I=2.5, N=3.0
• In propanone, the C=O bond is more polar than the C-H bond due to the difference in electronegativity
• Cl is more electronegative than C, causing electrons to flow from C to Cl, resulting in a negatively charged inductive effect
• Alkyl groups like methyl (CH3) and ethyl (C2H5 or CH3CH2) have a positively charged inductive effect, releasing electrons
• Homolytic fission involves the even distribution of bonded electrons, forming radicals which are highly reactive
• Heterolytic fission results in one atom or group taking both electrons, forming positive and negative ions
• During organic reactions, reagents either accept or donate electrons, categorized as electrophilic or nucleophilic reagents