Organic Chemistry Basics

Organic Chemistry Basics

• Organic chemistry is the study of hydrocarbons and their derivatives.
• The most common bonding in organic compounds is covalent bonding.
• Covalent bonds are classified into sigma and pi bonds based on orbital overlap.
• A sigma bond is formed by end-to-end orbital overlap and is stronger than a pi bond.
• A pi bond is formed by sideways orbital overlap and is weaker than a sigma bond.
• In a carbon atom with multiple bonds, the first bond is a sigma bond; subsequent bonds are pi bonds.

Hybridization

• sp³ Hybridization: occurs when a carbon atom forms four sigma bonds.
• sp² Hybridization: occurs when a carbon atom forms three sigma bonds and one pi bond.
• sp Hybridization: occurs when a carbon atom forms two sigma bonds and two pi bonds.

Types of Carbon

• Primary carbon (1°): A carbon atom bonded to one other carbon atom.
• Secondary carbon (2°): A carbon atom bonded to two other carbon atoms.
• Tertiary carbon (3°): A carbon atom bonded to three other carbon atoms.
• Quaternary carbon (4°): A carbon atom bonded to four other carbon atoms.

IUPAC Nomenclature Rules

• The order for naming a molecule follows these rules:
  • 2° prefix (for substituents/branching). Position indicated by a number.
  • 1° prefix (for closed chains, "cyclo-" prefix).
  • Word Root (number of carbons in the main chain).
  • 1° suffix (linkages: single, double, or triple bonds).
    • Single bond: -ane
    • Double bond: -ene
    • Triple bond: -yne
  • 2° suffix (functional group).

Straight Chain Hydrocarbon Naming

• The main chain is the longest carbon chain.
• Numbering starts at the end closest to a double or triple bond.
• The IUPAC name follows this structure: Word root-Number-1° suffix.
  • Example: C-C=C-C is But-2-ene.

Carbon Chain Naming

• The longest carbon chain determines the word root.
• 2° prefixes are used for branches, numbered.
• Word root is for the main chain.
• 1° suffix indicates linkages (single, double, or triple bonds).
• 2° suffix indicates the functional group.

Naming Organic Compounds: Introducing IUPAC Nomenclature

• IUPAC provides a standardized naming system for organic compounds.
• Alphabetical order is prioritized for prefixes and suffixes.
• The term "hex" represents a six-carbon chain.
• Double and triple bonds are denoted by "-ene" and "-yne", respectively, with numbering for position.
• For multiple "enes" or "ynes", use prefixes like "di," "tri."
• Alphabetical order determines priority between "-ene" and "-yne" at the same position.

Understanding 'Tie-Breakers'

• Alphabetical order of suffixes ("ene" before "yne") resolves tie-breaking situations with double and triple bonds.
• Same applies to branching with functional groups at different positions.
• Prefixes "di," "tri," etc., denote multiple branches.

Naming Branched Chain Hydrocarbons

• Identify the longest carbon chain (including multiple bonds) as the main chain.
• Number the main chain from the end giving the lowest numbers to branches.
• Name branches using "-yl" (methyl, ethyl, etc.).

Naming Closed-Chain Hydrocarbons

• The "cyclo" prefix denotes closed rings.
• The number of carbons in a ring is used in the root name (e.g., cyclopropane).
• Lowest number assigned to the double bond in a closed chain.
• Branches are named, the cyclo prefix is added, followed by the ring root, and the suffix for the carbon-carbon bond type.
• Example: 1-methylcyclopropane.

Naming Organic Compounds

• Rules for numbering carbons: Start from the end giving the lowest number to functional groups. Highest priority functional groups determine lowest numbering position.
• Highest priority functional groups:
  • Carboxylic acids
  • Aldehydes
  • Ketones
  • Alcohols
  • Alkenes
  • Alkynes
• Closed chain rules: Use "cyclo-" followed by the corresponding alkane's name, numbering from the functional group with the highest priority
• Functional groups and common names:
  • Aldehydes (-CHO): Suffix "al," e.g., propanal (propyl aldehyde)
  • Ketones (-C=O): Suffix "one," e.g., butanone (methyl ethyl ketone)
  • Alcohols (-OH): Suffix "ol," e.g., ethanol (ethyl alcohol)
  • Carboxylic acids (-COOH): Suffix "oic acid," e.g., ethanoic acid (acetic acid)
  • Ethers (R-O-R'): Alkoxyalkane, e.g., methoxypropane.
  • Esters: Alkyl alkanoate, e.g., ethyl ethanoate.
  • Halides (X): Haloalkane, e.g., 2-bromopropane.

Substituted Benzenes

• Common and IUPAC naming: -Phenol (hydroxybenzene), Aniline (aminobenzene), Nitrobenzene, Toluene (methylbenzene), Benzoic acid, Acetophenone (methyl phenyl ketone, acetylbenzene).

Positional Isomers

• Ortho, Meta, Para:
  • Ortho: Adjacent carbons
  • Meta: One carbon apart
  • Para: Opposite carbons
• Naming substituted benzenes: Numerical or ortho, meta, para prefixes are used.
• Priority rules: Highest priority functional group is the main group, numbering from it.

Naming Organic Compounds (continued)

• Priority order for functional groups is crucial.
• Alcohols have higher priority than halogens. Main chain includes the alcohol-containing carbon at the lowest number.
• Branches are named alphabetically.
• Example: 1-bromo-5-chloro-4-methylhexan-3-ol.
• Aldehyde has higher priority than ketone in the chain selection.
• Example: 3-oxo-2-methylhexanal.

Isomerism

• Isomers have the same molecular formula but different structures/arrangements.
  • Structural isomers: Different connectivity of atoms
  • Stereoisomers: Same connectivity, different spatial arrangement.

Structural Isomerism

• Chain isomerism: Different chain lengths.
• Position isomerism: Different positions of functional groups/substituents.
• Functional isomerism: Different functional groups.
• Metamerism: Different alkyl groups attached to the functional group.
• Ring-chain isomerism: Ring or chain structure.
• Examples of chain isomers: butane/2-methylpropane, pentane/2-methylbutane, etc.
• Examples of positional isomers: 1-chloropropane/2-chloropropane, but-1-ene/but-2-ene. etc.
• Examples of functional isomers: ethanol/methoxyethane, propanal/propanone. etc.
• Examples of metamers: methoxypropane/ethoxyethane, ethyl propyl ether/diethyl ether.
• Examples of ring-chain isomers: cyclopropane/propene.

General Organic Chemistry (GOC)

• GOC studies organic compounds' structures, bonding, properties, and reactions, especially those with functional groups.
• Bond fission: Breaking covalent bonds between atoms.
• Heterolytic fission: Electrons from the bond transferred to one atom, forming ions.
• Homolytic fission: Each atom receives one electron from the bond, forming free radicals.
• Heterolytic fission common in polar bonds, homolytic fission common in nonpolar bonds, or with light or heat energy.
• Free radicals are reactive due to unpaired electrons.

Key Points about Bond Fission (continued)

• Heterolytic fission forms ions (cation and anion).
• Homolytic fission forms free radicals.
• Polar solvents favour heterolytic fission, non-polar favour homolytic or heat/light energy.