29.1 Formulae, Functional Groups, and Naming of Organic Compounds:
- Functional Groups: Functional groups are specific groups of atoms within organic compounds that determine their physical and chemical properties. Examples of functional groups include alcohols, aldehydes, ketones, carboxylic acids, esters, amines, amides, and halogens.
- Formulae Representation:
- General Formula: Represents a class of compounds and shows the ratio of atoms.
- Structural Formula: Shows the arrangement of atoms and bonds in a molecule.
- Displayed Formula: Shows all atoms and bonds explicitly.
- Skeletal Formula: Simplified representation where carbon atoms and hydrogen atoms bonded to them are not shown explicitly.
- Systematic Nomenclature: Systematic nomenclature (IUPAC) is used to name organic compounds systematically based on the type and arrangement of functional groups. It involves identifying the longest carbon chain, numbering the carbons, and naming substituents or functional groups using prefixes and suffixes.
- Naming Aliphatic Compounds: Aliphatic compounds are organic compounds that do not contain aromatic rings. The systematic nomenclature for aliphatic compounds includes naming the main chain, indicating the functional group, and numbering the carbons to locate substituents.
- Naming Aromatic Compounds: Aromatic compounds contain a benzene ring or other aromatic rings. The systematic nomenclature for aromatic compounds involves numbering the carbons on the ring, indicating the substituents' positions using prefixes or numbers, and specifying the functional groups present.
29.2 Characteristic Organic Reactions:
- Terminology:
- Electrophilic Substitution: A reaction mechanism where an electrophile (electron-deficient species) replaces a functional group or atom in an organic molecule.
- Addition-Elimination: A reaction mechanism where an initial addition of a species to a molecule is followed by an elimination of another species.
29.3 Shapes of Aromatic Organic Molecules; σ and π Bonds:
- Shape of Aromatic Molecules: Aromatic molecules, such as benzene, have a planar structure. The carbon atoms in the benzene ring are sp2 hybridized, resulting in trigonal planar geometry. The π electrons in the ring form a delocalized π system above and below the plane of the ring.
- σ and π Bonds: σ (sigma) bonds are formed by the overlap of atomic orbitals along the bond axis, providing rotational stability to the molecule. π (pi) bonds result from the side-by-side overlap of p orbitals above and below the plane of the benzene ring, creating a delocalized electron system.
29.4 Isomerism: Optical:
- Enantiomers: Enantiomers are stereoisomers that are non-superimposable mirror images of each other. They have identical physical and chemical properties except for their ability to rotate plane-polarized light and their interaction with other chiral compounds.
- Optical Activity and Racemic Mixture: Enantiomers are optically active and rotate the plane of polarized light in opposite directions. A racemic mixture is a mixture of equal amounts of both enantiomers, which results in no net optical activity.
- Effect on Plane-Polarized Light: One enantiomer rotates plane-polarized light clockwise (dextrorotatory, labeled as "+"), while the other rotates it counterclockwise (levorotatory, labeled as "-").
- Relevance of Chirality in Drug Synthesis:
- Different Biological Activity: Enantiomers may exhibit different biological activities. For pharmaceuticals, only one enantiomer may possess the desired therapeutic effect.
- Separation of Racemic Mixtures: To obtain pure enantiomers, a racemic mixture needs to be separated by techniques such as chromatography or enzymatic resolution.
- Chiral Catalysts: Chiral catalysts can be used in asymmetric synthesis to selectively produce a single pure optical isomer.
Note: The knowledge of meso compounds and nomenclature of diastereoisomers is not required.