Chemistry
Isomerism
Isomerism refers to the phenomenon where two or more chemical compounds have the same molecular formula but different structural arrangements, leading to distinct properties. This can occur due to differences in the spatial arrangement of atoms or the presence of different functional groups. Isomerism is important in understanding the diversity of organic compounds and their varying behaviors.
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10 Key excerpts on "Isomerism"
eBook - ePubCarbohydrate Chemistry
Fundamentals and Applications
- Raimo Alén(Author)
- 2018(Publication Date)
- WSPC(Publisher)
3. Isomerism
3.1.General
A general molecular formula (e.g., Cx Hy Oz Nn ) expresses the kind and number of the constituent atoms of a compound, but it insufficiently represents the structure of the compound in question. A molecular formula can thus correspond to several compounds (isomers) that normally have different chemical and physical properties. Isomers can be defined as chemical compounds with identical molecular formulas (i.e., contain the same number of atoms of each element) that differ from one another in the arrangements of their atoms. This phenomenon is called “Isomerism” (in Greek, “isos” means “equal” and “meros” “part”), and it is divided into two main types (Fig. 3.1 ): (i)constitutional Isomerismor structural Isomerism and (ii)stereoIsomerismor space Isomerism. Upon examining certain isomers (such as aldoses with the same number of carbon atoms), one does not necessarily find differences based on constitutional Isomerism, and finding the actual differences requires detailed comparison of the stereoisomeric properties of the structures.Constitutional Isomerism can be divided into three subgroups: (i)functional group Isomerism(“function Isomerism”), (ii)chain Isomerism(“skeletal Isomerism”), and (iii)position Isomerism(“regioIsomerism”), which are discussed in the next chapters with the help of illustrative examples. The general name “structural Isomerism” is traditionally used for “constitutional Isomerism”. However, since the structure of the compounds can be thought to cause all Isomerism, the use of the former term is not recommended.Fig. 3.1.The main types of Isomerism and their subtypes.The branch of organic chemistry that examines the three-dimensional structures of molecules,stereochemistry, has gained importance when striving to understand the physical and chemical properties of various compounds. In carbohydrate chemistry, it is also essential to know the stereochemical structure of the compounds. StereoIsomerism can be seen to generally represent the form of Isomerism where compounds with the same chemical structure (i.e., the order of attachment of the atoms involved and the location of the bonds between them) differ from each other only in the spatial direction of their atoms or atom groups. This Isomerism is divided into (i)optical Isomerism(“physical Isomerism”), (ii)conformational Isomerism, and (iii)geometric Isomerism(“cis/trans
eBook - ePubUnderstanding Advanced Organic and Analytical Chemistry
The Learner's ApproachRevised Edition
- Kim Seng Chan, Jeanne Tan;;;(Authors)
- 2016(Publication Date)
- WS EDUCATION(Publisher)
CHAPTER 2
Isomerism in Organic Compounds
2.1 Introduction
If a molecule has the molecular formula C4 H8 , does it imply that all the C4 H8 molecules are identical? The alkene, but-1-ene, whose molecule is shown below, has the molecular formula C4 H8 .Yet, C4 H8 also represents the formula for cyclobutane, which belongs to the cycloalkane family:Compounds that have the same molecular formula but different structures are known as isomers. This phenomenon is known as Isomerism. The two main types of Isomerism are constitutional/ structural Isomerism and stereoIsomerism. These are further divided into subclasses of which some are discussed in this chapter. Isomers generally have different physical and chemical properties, but they can also have similar chemical properties if they contain the same functional groups. Each specific functional group possesses a characteristic set of chemical reactions.2.2 Constitutional/Structural Isomerism
Constitutional/structural isomers are compounds with the same molecular formula but different structures or structural formulae. Both but-1-ene and cyclobutane constitute a pair of constitutional/structural isomers. The difference in structures can be attributed to either a difference in the arrangement of atoms or due to the presence of different functional groups.Based on the above definitions, constitutional/structural Isomerism can be classified into three main types:• chain Isomerism;• positional Isomerism; and• functional group Isomerism.2.2.1 Chain Isomerism
Compounds that exhibit chain Isomerism with each other have the same functional group but differ in the way the carbon atoms are connected in the mainskeletal carbon chain of their molecules. In other words, these molecules differ in the degree of branching, hence the term chain isomers
eBook - ePubIntroductory Organic Chemistry and Hydrocarbons
A Physical Chemistry Approach
- Caio Lima Firme(Author)
- 2019(Publication Date)
- CRC Press(Publisher)
Chapter ThirteenIsomerism
Isomerism AND TYPES OF Isomerism
Isomerism gives rise to isomers that are molecules with the same chemical formula but different structural parameters or different spacial structures (different type of branching or different type of functional group or different position of the same functional group or different arrangement of substituents or different absolute configuration of the asymmetric atom).As for structural Isomerism, there are three types: chain Isomerism, position Isomerism (or regioIsomerism), and functional Isomerism.The chain Isomerism is related to the different position of the branching in its main chain. For example, butane and 2-methyl-propane are isomers (C4 H10 ); pentane, 2-methyl-butane and 2,2-dimethyl-propane are isomers (C5 H12 ); but-1-ene and 2-methyl propene are isomers (C4 H8 ) as well (see Fig. 13.1(A) ).Figure 13.1 Bond line formula of (A) chain isomers, (B) regioisomers, and (C) functional isomers.The position Isomerism (or regioIsomerism) is related to a different position of the substituent group or functional group in the molecule. For example, but-1-ene and but-2-ene are isomers (C4 H8 ), pentan-2-one and pentan-3-one are isomers (C5 H10 O), 2-chloro-propane and 1-chloro-propane are isomers (C3 H7 Cl), orto-dichlorobenzene and para-dichlorobenzene are isomers (C6 H4 Cl2 ) as well (see Fig. 13.1(B) ).Functional Isomerism is related to different functional groups with the same molecular formula. For example, propanone and propanal are isomers (C3 H6 O), hexan-1-ene and cyclohexane (C6 H12 ) are isomers as well (see Fig. 13.1(C) ).StereoIsomerism is related to specific arrangements of substituents where two isomers are differentiated by their spacial disposition. Stereo means spacial.GEOMETRIC STEREOIsomerism
Geometric stereoisomerm occurs in alkenes or derivatives and in substituted cycloalkanes. They generate two isomers called cis and trans or E and Z.
eBook - PDF- Rose Marie O. Mendoza(Author)
- 2020(Publication Date)
- Arcler Press(Publisher)
In addition to it, quantitative information on the conformational behavior of molecules in solution is also provided by the study of the temperature dependence of NMR spectra. 1.3. ISOMERS AND STEREOCHEMISTRY Isomers are defined as compounds with the same molecular formula but differ in structure. Isomers can be further classified as structural or constitutional and stereoisomers. Structural isomers are substances (with the same molecular formula) but differ in the arrangement or placement of atoms in the compound, which will make their condensed structure different from each other. The changes connectivity of the carbon atoms is also one of the distinct features of constitutional isomers. In stereoisomers, the atoms are connected sequentially in the same way, such that condensed formulas for the two molecules are identical. The isomers differ, however, in the way the atoms are arranged in space. There are two major sub-classes of stereoisomer; conformational isomers, which interconvert through rotations around single bonds, and configurational isomers, which are not readily interconvertible. Chiral compounds, on the other hand, are defined as the compounds which are having the same molecular and condensed structural formula, but vary in the orientation of four distinct groups that are around the atom of carbon. These are chiral compounds and geometric isomers or isomeric compounds that are present in the orientation of atoms on a double bond or ring system. Often, they are referred as stereoisomers since they belong to both categories (Figure 1.3). Basic Stereochemistry of Organic Molecules 8 Figure 1.3. Classification of isomer in stereochemistry . Source: Image by Wikimedia commons. Conformational analysis studies about the different orientations that can be achieved by the molecules and the way their energy changes as their atoms are rotated in space, therefore, becomes important since these will draw the distinction between one molecule over the other.
eBook - PDF- David R. Klein(Author)
- 2020(Publication Date)
- Wiley(Publisher)
Such compounds are called stereoiso- mers, and we will explore the connection between stereoIsomerism and drug action. This chapter will focus on the different kinds of stereoisomers. We will learn to identify stereoisomers, and we will learn several drawing styles that will allow us to compare stereoisomers. The upcoming chapters will focus on reactions that produce stereoisomers. 5.1 OVERVIEW OF Isomerism The term isomers comes from the Greek words isos and meros, meaning “made of the same parts.” That is, isomers are compounds that are constructed from the same atoms (same molecular formula) but that still differ from each other. We have already seen two kinds of isomers: constitutional isomers (Section 4.3) and stereoisomers (Section 4.14), as illustrated in Figure 5.1. FIGURE 5.1 The main categories of isomers. Isomers Stereoisomers Constitutional isomers Same molecular formula but different constitution (order of connectivity of atoms) Same molecular formula and constitution but different spatial arrangement of atoms DO YOU REMEMBER? Before you go on, be sure you understand the following topics. If necessary, review the suggested sections to prepare for this chapter. • Constitutional Isomerism (Section 1.2) • Tetrahedral Geometry (Section 1.10) • Drawing and Interpreting Bond-Line Structures (Section 2.2) • Three-Dimensional Representations (Section 2.6) Constitutional isomers differ in the connectivity of their atoms; for example: Ethanol Boiling point = 78.4°C C C O H H H H H H Methoxymethane Boiling point = –23°C C O C H H H H H H The two compounds above have the same molecular formula, but they differ in their constitution. As a result, they are different compounds with different physical properties. Stereoisomers are compounds that have the same constitution but differ in the spatial arrange- ment of their atoms.
eBook - PDFChemistry for Technologists
The Commonwealth and International Library: Electrical Engineering Division
- G. R. Palin, N. Hiller(Authors)
- 2014(Publication Date)
- Pergamon(Publisher)
SECTION V ORGANIC CHEMISTRY This page intentionally left blank CHAPTER 13 Isomerism and Formulae Multiplicity of Organic Compounds The ability of carbon atoms to bond with one another in large numbers, as well as forming bonds with atoms of other elements, has been mentioned in Chapter 1. It was also mentioned that this results in there being an enormous number of carbon containing compounds. Where oxygen only forms two stable compounds with hydrogen, carbon forms millions. Where hydrogen, nitrogen and oxygen form three stable compounds, hydro-gen, nitrogen and carbon form millions, and so on. This has led to the separation of the study of carbon containing compounds from the study of the compounds of the other elements. It has also led to a somewhat different technique for naming compounds and writing formulae, which is necessary because of the widespread occurrence of Isomerism amongst organic compounds. Isomers can be defined as compounds with the same molecular formula, but differing in one or more of their chemical or physical properties. Iso-merism does occur in inorganic compounds, but only to a limited extent, and the number of isomers corresponding to a given molecular formula is small. Isomerism occurs in all but the simplest organic compounds, and the number of isomers can be very large. For instance, the relatively simple molecular formula C 8 H 18 applies to eighteen different isomers. Structural Isomerism Structural Isomerism occurs when the chemical bonds holding the atoms together in the different molecules, are different. One of the simplest examples of this type of Isomerism occurs in the two compounds having the molecular formula C 2 H e O . In both, the carbon is in the sp 3 hybrid state, i.e. it forms four single covalent bonds, tetrahedrally orientated. The oxygen atom forms two covalent bonds, involving the two unpaired 2p electrons, and each hydrogen atom forms one covalent bond, involving the unpaired Is electron.
eBook - PDF- David R. Klein(Author)
- 2016(Publication Date)
- Wiley(Publisher)
Such compounds are called stereoisomers, and we will explore the connection between stereoIsomerism and drug action. This chapter will focus on the different kinds of stereoisomers. We will learn to identify stereoisomers, and we will learn several drawing styles that will allow us to compare stereoisomers. The upcoming chapters will focus on reactions that produce stereoisomers. 5.1 Overview of Isomerism The term isomers comes from the Greek words isos and meros, meaning “made of the same parts.” That is, isomers are compounds that are constructed from the same atoms (same molecular formula) but that still differ from each other. We have already seen two kinds of isomers: constitutional isomers (Section 4.3) and stereoisomers (Section 4.14), as illustrated in Figure 5.1. FIGURE 5.1 The main categories of isomers. Isomers Stereoisomers Constitutional isomers Same molecular formula but different constitution (order of connectivity of atoms) Same molecular formula and constitution but different spatial arrangement of atoms DO YOU REMEMBER? Before you go on, be sure you understand the following topics. If necessary, review the suggested sections to prepare for this chapter. • Constitutional Isomerism (Section 1.2) • Tetrahedral Geometry (Section 1.10) • Drawing and Interpreting Bond-Line Structures (Section 2.2) • Three-Dimensional Representations (Section 2.6) Take the DO YOU REMEMBER? QUIZ in to check your understanding. Constitutional isomers differ in the connectivity of their atoms; for example: Ethanol Boiling point = 78.4°C C C O H H H H H H Methoxymethane Boiling point = –23°C C O C H H H H H H The two compounds above have the same molecular formula, but they differ in their constitution. As a result, they are different compounds with different physical properties. Stereoisomers are compounds that have the same constitution but differ in the spatial arrange- ment of their atoms.
- Morris Hein, Scott Pattison, Susan Arena, Leo R. Best(Authors)
- 2014(Publication Date)
- Wiley(Publisher)
©Joachim Ladefoged/VII/CORBIS 26.1 Review of Isomerism 26.2 Plane-Polarized Light and Optical Activity 26.3 Fischer Projection Formulas 26.4 Enantiomers 26.5 Racemic Mixtures 26.6 Diastereomers and Meso Compounds STEREOIsomerism The mirror image of this children’s ballet class is not superimposable on the class. C H A P T E R O U T L I N E M any of us grew up hearing such comments as “Can’t you tell your left from your right?” Have you ever watched a small child try to differentiate between a right and left shoe? Not surprisingly, the distinction between right and left is difficult. After all, our bodies are reasonably symmetrical. For example, both hands are made up of the same components (four fingers, a thumb, and a palm) ordered in the same way (from thumb through little finger). Yet there is a difference if we try to put a left-handed glove on our right hand or a right shoe on our left foot. Molecules possess similar, subtle structural differences, which can have a major impact on their chemical reactivity. For example, although there are two forms of blood sugar, related as closely as our left and right hands, only one of these structures can be used by our bodies for energy. StereoIsomerism is a subject that attempts to define these subtle differences in molecular structure. StereoIsomerism is an amazing phenomenon; it is where some compounds find a partner—their mirror image. C H A P T E R 26 672 CHAPTER 26 • StereoIsomerism TABLE 26.1 Why Are Stereoisomers Important to Biochemistry? Answer Comment #1 The great majority of biochemicals are stereoisomers. Understanding biochemical structures is difficult without a basic understanding of stereoIsomerism. #2 Metabolism is stereospecific. For example, glucose (blood sugar) is easily metabolized while its enantiomer (see Section 26.4) is not useable. 26.1 REVIEW OF Isomerism Distinguish structural isomers from stereoisomers.
eBook - PDFOrganic Chemistry
A Mechanistic Approach
- Penny Chaloner(Author)
- 2014(Publication Date)
- CRC Press(Publisher)
221 7.1 INTRODUCTION We have previously discussed the existence of isomers of organic compounds—compounds that have the same molecular formula but a different construction. Isomers can be divided into two types—structural isomers and stereoisomers. For example, n-butane (7.1) and 2-methyl propane (7.2) are structural isomers—the atoms are joined together in a different way. Structural isomers are described as having a different constitution. 7.1 7.2 Stereoisomers have the same constitution, with all the same atoms joined together by the same type of bonds but a different shape. The existence of stereoisomers depends on the theory of organic structure and the fact that chemical bonds have directional properties. Stereoisomers can be further divided into two mutually exclusive groups: enantiomers and diastereoisomers (sometimes elided as diastereomers). Enantiomers are distinguishable molecules related as object and mirror image. Diastereoisomers are all other stereoisomers. Although there are many computer programs allowing you to generate molecules on screen and move them around in space, physical models are also useful in understanding stereochemistry. “Ball and stick” models are useful to get an overall picture of a molecule, including the relative sizes of the atoms, but they tend to be quite expensive (Figure 7.1). Skeletal models allow you to see just the bonds in a molecule but give no idea of steric effects. The advantage is that they are generally quite inexpen- sive (Figure 7.2). “Space-filling” models focus attention on the atoms, rather than the bonds; they are excellent for studying steric effects, giving a clearer view of atom size (Figure 7.3). These are sometimes known as Corey, Pauling, Koltun (CPK) models where atoms are represented as overlapping spheres, with radii genuinely representative of atomic radii. They are frequently used to study biological interac- tions, such as the docking of drugs at receptors.
eBook - PDFFoundations of Chemistry
An Introductory Course for Science Students
- Philippa B. Cranwell, Elizabeth M. Page(Authors)
- 2021(Publication Date)
- Wiley(Publisher)
E and Z Isomerism and chirality are both types of stereoIsomerism. 12.3.1 Chain Isomerism Chain Isomerism occurs when the longest chain length in an alkane varies. For example, butane and 2-methylpropane both have the same molecular formula, C 4 H 10 , but the atoms have different connectivities (Figure 12.7). Structural isomers have the same molecular formula but a different spatial arrangement of atoms. 12.3 Isomers 413 In this case, the different arrangement of atoms has a large impact upon the physical properties of butane and 2-methylpropane, although their chemical reactivity is very similar. Butane has a melting point of -138 C and boiling point of -0.5 C, whereas 2-methylpropane has a melting point of -160 C and boiling point of -12 C. The reason for the difference is that in butane, there are stronger intermolecular forces between molecules because they can align much more closely (Figure 12.8). 12.3.2 Positional Isomerism Positional Isomerism means that, in a homologous series of compounds, the same functional group is present but is located in different positions along a chain. This type of Isomerism is commonly encountered with alcohols. Figure 12.9 shows the two positional isomers for butanol: butan-1-ol and butan-2-ol. Although butan-1-ol and butan-2-ol are positional isomers, they are still members of the same homologous series (alcohols) and have similar chemical reactivity but different physical properties. 12.3.3 Functional group Isomerism With functional group Isomerism, the molecular formula is the same, but the functional groups present are different. This can have a major impact on both the chemical reactivity and physical properties of a compound. For example, two compounds have molecular formula C 2 H 6 O: ethanol and methoxy-methane, containing an alcohol and an ether, respectively (Figure 12.10). butane 2-methylpropane Figure 12.7 Chain isomers of C 4 H 10 . (a) (b) Figure 12.8 (a) Butane molecules; (b) 2-methylpropane molecules.
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