Chemistry
Metamerism
Metamerism refers to the phenomenon in organic chemistry where compounds have the same molecular formula but differ in the arrangement of atoms within the molecule. This results in different structural isomers with distinct chemical and physical properties. Metamerism is commonly observed in organic compounds containing heteroatoms, such as oxygen, nitrogen, or sulfur, leading to variations in functional groups and bonding patterns.
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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.
- Morris Hein, Scott Pattison, Susan Arena, Leo R. Best(Authors)
- 2014(Publication Date)
- Wiley(Publisher)
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. Isomerism is the phenomenon of two or more compounds having the same number and kinds of atoms. (See Section 19.7.) There are two types of isomerism. In the first type, known as struc- tural isomerism, the difference between isomers is due to different structural arrangements of the atoms that form the molecules. For example, butane and isobutane (C 4 H 10 ), ethanol and dimethyl ether, (C 2 H 6 O) and 1-chloropropane and 2-chloropropane (C 3 H 7 Cl) are structural isomers: CH 3 CH 2 CH 2 CH 3 CH 3 CH 2 OH CH 3 CH 2 CH 2 Cl butane ethanol 1-chloropropane CH 3 OCH 3 CH 3 CHClCH 3 methoxymethane 2-chloropropane (dimethyl ether) In the second type of isomerism, the isomers have the same structural formulas but differ in the spatial arrangement of the atoms. This type of isomerism is known as stereoisomerism. Thus, compounds that have the same structural formulas but differ in their spatial arrange- ment are called stereoisomers. There are two types of stereoisomers: cis–trans or geometric isomers, which we have already considered, and optical isomers, the subject of this chapter. One outstanding feature of optical isomers is that they have the ability to rotate the plane of plane-polarized light. Stereoisomerism exists in all biological systems. (See Table 26.1.) KEY TERMS stereoisomerism stereoisomer LEARNING OBJECTIVE LEARNING OBJECTIVE CH 3 CHCH 3 CH 3 2-methylpropane (isobutane) 26.2 PLANE-POLARIZED LIGHT AND OPTICAL ACTIVITY Describe plane-polarized light and how chiral carbons demonstrate optical activity. Plane-polarized light is light that is vibrating in only one plane.
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.
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