Isomer
An isomer is a type of molecule that shares the same number of atoms of each element as another molecule but differs in its atomic structure. This results in isomers having identical molecular formulas while exhibiting varying chemical and physical properties. Isomers are categorized into two primary types: structural isomers, which are connected in different ways, and stereoisomers, which maintain the same connectivity but differ in spatial arrangement. For instance, glucose and fructose, both with the formula C₆H₁₂O₆, are isomers that are absorbed differently by the body despite having the same composition. Structural isomers may have variations like 1-propanol and 2-propanol, differing in the placement of functional groups. Stereoisomers can include enantiomers, which are mirror images of each other, and conformational isomers, which arise from rotations around single bonds. Overall, the concept of isomerism highlights the complexity and diversity of molecular structures and their implications in chemistry and biology.
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Isomer
An isomer is a type of molecule that has the same number of identical atoms as another molecule but with a different atomic structure. This means that isomers can share the same molecular formula, but the varying arrangement of their atoms can give them different chemical or physical properties. For example, glucose and fructose are two types of sugar molecules with the same number of carbon, hydrogen, and oxygen atoms. However, the molecules are found in various foods and are not absorbed by the body in the same way. Isomers can be divided into two general types based on how the bonds that hold the atoms together are arranged. In stereoisomers, the individual atoms in two molecules are arranged in numerous shapes; while the atoms in structural isomers keep their shape but are connected in various manners.
Background
Atoms are the smallest fundamental units of matter and are themselves comprised of even smaller particles called protons, neutrons, and electrons. The protons and neutrons form the nucleus, or core, of an atom, while the electrons orbit the nucleus in a series of shells. The number of protons in an atom determines the type of element it is. For example, hydrogen has one proton, oxygen has eight, and silver has forty-seven. Typically, atoms have the same number of electrons as protons.
Molecules are atoms that are joined together by chemical bonds. These bonds are formed by the electrons orbiting in the outer shell of the atoms. Depending on the number of shells in an atom, the outer shell can hold a varying number of electrons. When the outer shell is full, that atom is considered to be stable and does not bond well with other atoms. If the outer shell is not full, atoms seek stability by bonding with other atoms to fill that shell. Atoms can bond together by either transferring or sharing electrons with other atoms.
For example, carbon is an element that bonds easily to other atoms. A carbon atom has four electrons out of a maximum of eight in its outer shell. This allows carbon atoms to form bonds with other carbon atoms and a wide variety of other elements. A carbon atom bonded with two oxygen atoms forms carbon dioxide, a molecule with the chemical formula CO2. A carbon atom that bonds with four atoms of hydrogen forms the gas methane, a molecule written as CH4.
Overview
Isomers—a name derived from the Greek iso- (equal) and meros (share)—are molecules or chemical compounds that are made up of the same type and number of atoms but are bonded together in different ways. Isomers have the same chemical formulas, but their various structures can give them different chemical or physical properties. Isomers can occur in two main types: structural isomers or stereoisomers. Structural isomers, also known as constitutional isomers, have the same chemical formulas but are connected in numerous ways. Stereoisomers also have the same formulas and maintain the same connectivity but are arranged in various physical shapes.
The organic compound known as propanol is an example of a structural isomer. Propanol is an alcohol comprised of three carbon atoms, eight hydrogen atoms, and one oxygen atom with a chemical formula of C3H8O. Propanol has two isomers that are differentiated by the placement of the oxygen atom. In the isomer 1-propanol, the oxygen atom is bonded to one of the outside carbon atoms. This propanol isomer is used in printing ink, window cleaner, polishing products, and several other applications. If the oxygen atom is bonded to the central carbon atom, the isomer 2-propanol is formed. This substance is also known as isopropyl alcohol, or rubbing alcohol, and is commonly used as a household medical disinfectant. In a third propanol isomer—methoxyethane—the oxygen atom is part of the central structure of the molecule, rather than connected to a single carbon atom. Methoxyethane is a highly flammable, poisonous substance used in diesel fuel or as a refrigerant.
Glucose and fructose are isomers with the chemical formula of C6H12O6. In glucose, one of the oxygen atoms is bonded to the first carbon atom in the molecule. In fructose, that oxygen atom is bonded to the second carbon atom. Glucose is a sugar that is a primary source of energy for the body and found in carbohydrates. Fructose is a sugar found in fruits and vegetables. It is absorbed by the body much faster than glucose and produces more fat.
Stereoisomers are isomers in which an individual atom or group of atoms is bonded to the same place but rearranged in a different geometric position. Stereoisomers are themselves divided into three types: enantiomers, diastereomers, and conformational isomers. Enantiomers are isomers with a mirror-image structure; diastereomers are not mirror images; and conformational isomers have an atom or group of atoms that rotates around a single bond.
Enantiomers, or optical isomers, are non-superimposable mirror images of each other, similar to how a person’s hands look when placed next to each other. Lactic acid (C3H6O3)—a substance produced in the bloodstream and by bacteria in yogurt—can be “flipped” into isomers oriented to the left or right. Diastereomers are non-superimposable isomers that are also not mirror images of each other. They are sometimes difficult to identify because they may or may not have a common central area. An industrial chemical known as 3-chloro-2-butanol (C4H9ClO) can exist in four types of isomers in which pairings appear to be flipped around a central “spine” of two carbon atoms.
Conformational isomers can only occur when atoms or groups of atoms are joined together by a single bond. A single bond is a chemical bond in which one pair of electrons is shared between two atoms. Double and triple bonds—in which two or three pairs of electrons are shared—cannot rotate around a common atom to form a conformational isomer. For example, butane (C4H10)—a flammable hydrocarbon often used as fuel—can form three isomers by rotating smaller groupings of hydrogen and carbon atoms.
Bibliography
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