Organic Chemistry – Some Basic Principles and Techniques

• After studying organic chemistry principles and techniques, students will be able to:

  • Understand reasons for the tetravalence of carbon and shapes of organic molecules
  • Write structures of organic molecules in various ways
  • Classify organic compounds
  • Name compounds according to the IUPAC system of nomenclature and derive their structures from given names
  • Understand organic reaction mechanisms
  • Explain the influence of electronic displacements on the structure and reactivity of organic compounds
  • Recognize types of organic reactions
  • Learn techniques for purifying organic compounds
  • Write chemical reactions involved in the qualitative analysis of organic compounds
  • Understand the principles involved in the quantitative analysis of organic compounds
• Carbon forms covalent bonds with other carbon atoms and atoms of elements like hydrogen, oxygen, nitrogen, sulphur, phosphorus, and halogens due to catenation
• Organic compounds are essential for life and have applications in materials like clothing, fuels, polymers, dyes, and medicines
• Around 1780, chemists began distinguishing between organic compounds from plants and animals and inorganic compounds from mineral sources
• The synthesis of organic compounds from inorganic sources in a laboratory by chemists like Wohler, Kolbe, and Berthelot challenged the idea of a 'vital force' in organic compound formation
• The electronic theory of covalent bonding shaped modern organic chemistry
• The shapes of carbon compounds are explained by the use of sp3, sp2, and sp hybrid orbitals by carbon atoms in molecules like methane, ethene, and ethyne
• Hybridization influences bond length, bond strength, and electronegativity in carbon compounds
• In π bond formation, parallel orientation of p orbitals on adjacent atoms is necessary for proper sideways overlap, providing reactive centers in molecules with multiple bonds
• Structures of organic compounds can be represented in various ways, including Lewis structures, condensed structures, and bond-line structural formulas
• Bond-line structural representation simplifies organic compound structures by using lines to represent carbon-carbon bonds in a zig-zag fashion
• Cyclic compounds can be represented in bond-line formulas, showing structures like cyclopropane, cyclopentane, and chlorocyclohexane
• Students can expand condensed formulas into complete structural formulas to represent organic compounds accurately
• Single-celled organisms have a short distance for substances to enter the cell
• Multicellular organisms have a larger distance due to a higher surface area to volume ratio
• Multicellular organisms require specialised exchange surfaces for efficient gas exchange of carbon dioxide and oxygen
• Alkyl groups are groups of atoms that are derived from alkanes
• Examples of alkyl groups include:

  • Methyl (abbreviated as Me)
  • Ethyl (abbreviated as Et)
  • Propyl (abbreviated as Pr)
  • Butyl (abbreviated as Bu)
• Alkyl groups can be branched, leading to different structures like isopropyl, sec-butyl, isobutyl, and tert-butyl groups
• Common branched groups have specific trivial names, such as n-propyl, isopropyl, sec-butyl, isobutyl, and tert-butyl groups
• The structural unit -CH2C(CH3)3 is called the neopentyl group
• Nomenclature of branched chain alkanes involves:

  1. Identifying the longest carbon chain in the molecule

  2. Numbering the carbon atoms of the parent chain to identify the parent alkane and locate branching positions

  3. Prefixing alkyl groups to the parent alkane name and indicating the positions of the substituents
• In naming compounds with multiple identical substituent groups, prefixes like di, tri, tetra, etc., are used
• If two substituents are in equivalent positions, the lower number is given to the one coming first in alphabetical order
• Branched alkyl groups are named following specific procedures, with the carbon atom of the branch attaching to the root alkane numbered as 1
• The compound with a methyl group attached at the 6th carbon is named 6-Methyloctan-3-ol
• For a compound with a ketone functional group, the suffix '-one' is used. If there are two keto groups, the suffix becomes 'dione'. For example, Hexane-2,4-dione
• In a compound with a carboxylic acid group, the parent chain is suffixed with 'oic acid'. The keto group is indicated by 'oxo'. An example is 5-Oxohexanoic acid
• A compound with two C=C functional groups at carbons 1 and 3, and a C≡C functional group at carbon 5 is named Hexa-1,3-dien-5-yne
• Heterolytic cleavage of bromomethane results in C+ H3 and Br–
• A carbon atom with a sextet of electrons and a positive charge is called a carbocation
• The H3 ion is known as a methyl cation or methyl carbonium ion
• Carbocations are classified as primary, secondary, or tertiary based on the number of carbons directly attached to the positively charged carbon
• Carbocations are highly unstable and reactive species
• Alkyl groups attached to the positively charged carbon stabilize carbocations due to inductive and hyperconjugation effects
• Carbocations have a trigonal planar shape with the positively charged carbon being sp2 hybridized
• A species in which carbon gets the shared pair of electrons is called a carbanion
• Carbanions are generally sp3 hybridized and have a distorted tetrahedral structure
• Carbanions are also unstable and reactive species
• Organic reactions that proceed through heterolytic bond cleavage are called ionic or heteropolar or polar reactions