Isomerism - FOS 127 Content Week 2 PDF

WEEK 2 SUB TOPIC: ISOMERISM Positional isomerism Chain isomerism Geometric and optical isomerism Drawing optical isomers in 3D  ISOMERISM This is a phenomenon shown by two or more organic compounds having the same molecular formula but different properties due to difference...

WEEK 2 SUB TOPIC: ISOMERISM Positional isomerism Chain isomerism Geometric and optical isomerism Drawing optical isomers in 3D  ISOMERISM This is a phenomenon shown by two or more organic compounds having the same molecular formula but different properties due to difference in arrangement of atoms along the carbon Skelton Isomerism occurs in two form i.e. structural isomerism and stereo isomerism. Stereoisomerism arises in compounds having the same chemical formula but different orientations of the atoms belonging to the molecule in three- dimensional space. The compounds that exhibit stereoisomerism are often referred to as stereoisomers. This phenomenon can be further categorized into two subtypes. Structural Isomerism is commonly referred to as constitutional isomerism. The functional groups and the atoms in the molecules of these isomers are linked in different ways. Different structural isomers are assigned different IUPAC names since they may or may not contain the same functional group.  TYPES OF STRUCTUAL ISOMERISM Positional isomerism-Occurs when functional groups are attached on different positions on the parent carbon chain. The positions of the functional groups or substituent atoms are different in position isomers. Typically, this isomerism involves the attachment of the functional groups to different carbon atoms in the carbon chain. An example of this type of isomerism can be observed in the compounds having the formula C3H7Cl. POSITION ISOMERISM EXAMPLE  CHAIN ISOMERISM Chain isomerism-Occurs when carbon atoms are linked to the main chain in different ways It is also known as skeletal isomerism. The components of these isomers display differently branched structures. Commonly, chain isomers differ in the branching of carbon An example of chain isomerism can be observed in the compound C5H12, as illustrated below CHAIN ISOMERISM EXAMPLE  FUNCTIONAL GROUP ISOMERISM Functional group isomerism-Form of isomerism where compounds are different due different arrangements of atoms leading to different functional groups. As the name suggests, it refers to the compounds that have the same chemical formula but different functional groups attached to them. An example of functional isomerism can be observed in the compound C3H6O FUNCTIONAL GROUP ISOMERISM EXAMPLE  METAMERISM This type of isomerism arises due to the presence of different alkyl chains on each side of the functional group. It is a rare type of isomerism and is generally limited to molecules that contain a divalent atom (such as sulphur or oxygen), surrounded by alkyl groups. Example: C4H10O can be represented as ethoxyethane (C2H5OC2H5) and methoxy-propane (CH3OC3H7).  TAUTOMERISM A tautomer of a compound refers to the isomer of the compound which only differs in the position of protons and electrons. Typically, the tautomers of a compound exist together in equilibrium and easily interchange. It occurs via an intramolecular proton transfer. An important example of this phenomenon is Keto-enol tautomerism.  RING-CHAIN ISOMERISM In ring-chain isomerism, one of the isomers has an open-chain structure whereas the other has a ring structure. They generally contain a different number of pi bonds. A great example of this type of isomerism can be observed in C3H6. Propene and cyclopropane are the resulting isomers, as illustrated below. RING-CHAIN ISOMERISM EXAMPLE  GEOMETRIC ISOMERISM Geometric isomerism-It is known as Cis-trans isomerism. Isomers differ in their spatial arrangement around a double bond These isomers have different spatial arrangements of atoms in three-dimensional space. An illustration describing the geometric isomerism observed in the acyclic But-2-ene molecule is provided below. GEOMETRIC ISOMERISM EXAMPLE  OPTICAL ISOMERISM Optical isomerism-Isomers have the same molecular and structural formulae but differ in their direction of rotation in plane polarized light. Compounds that exhibit optical isomerism feature similar bonds but different spatial arrangements of atoms forming non- superimposable mirror images. These optical isomers are also known as enantiomers. Enantiomers differ from each other in their optical activities. Dextro enantiomers rotate the plane of polarized light to the right whereas laevo enantiomers rotate it to the left, as illustrated below. OPTICAL ISOMERISM EXAMPLE