Organic molecules structural formulas

Table 14m this section sets forth the procedure to be followed m writ mg Lewis structures for organic molecules It begins with experimentally determined information the molecular formula and the constitution (order m which the atoms are connected)... 

Electron dot formulas are useful for deducing the structures of organic molecules, but it is more convenient to use simpler representations—structural or graphic formulas—in which a line is used to denote a shared pair of electrons. Because each pair of electrons shared between two atoms is equivalent to a total bond order of 1, each shared pair can be represented by a line between the symbols of the elements. Unshared electrons on the atoms are usually not shown in this kind of representation. The resulting representations of molecules are called graphic formulas or structural formulas. The structural formulas for the compounds (a) to (e) described in Example 21.1 may be written as follows ... 

Electron dot formulas are useful for deducing the structures of organic molecules, but it is more convenient to use simpler representations. In... 

The most usual representation of an organic molecule is the two-dimensional structural formula. Therefore, similarity of molecules is looked at as similarity of the structural formulas. Two molecules are stated to be similar if the structural scaffolds are similar and the substitution patterns are similar. 

Modern organic chemists rely on nuclear magnetic resonance spectroscopy for day-to-day identification of organic molecules. It is a powerful technique that allows one to count protons, identify the chemical environment (actually, the magnetic environment) of different protons, and predict how many neighbors each proton has. With this information, as well as the empirical formula and functional group information obtained from mass spectrometry and infrared spectroscopy, determination of the structure of organic molecules is usually feasible. 

The aforementioned names are systematic names, which are based on actual structural formulas of molecules. In addition, there are common names of organic compounds that do not indicate their structural formulas. Naming organic compounds is a complex topic, and no attempt is made in this chapter to teach it to the reader. Flowever, from the names of compounds given in this chapter and later chapters, some appreciation of the rationale for organic compound names shonld be obtained. 

With practice writing structural formulas for organic molecules soon becomes rou tine and can be simplified even more For example a chain of carbon atoms can be rep resented by drawing all of the C—C bonds while omitting individual carbons The result mg structural drawings can be simplified still more by stripping away the hydrogens... 

Predicting the Structures of Simple Organic Molecules from Their Formulas... 

This limitation was already painfully obvious to the organic chemists in the 1880s these are statie struetures, whereas of eourse any moleeule at any temperature is a jelly-like pulsating, librating and vibrating entity. Only a terribly simplistic eye would see a molecule frozen into this Platonic archetype of the structural formula. 

The following is a procedure recommended for elucidating the structure of complex organic molecules. It uses a combination of different NMR and other spectroscopic techniques. It assumes that the molecular formula has been deduced from elemental analysis or high-resolution mass spectrometry. Computer-based automated or interactive versions of similar approaches have also been devised for structural elucidation of complex natural products, such as SESAMI (systematic elucidation of structures by using artificial machine intelligence), but there is no substitute for the hard work, experience, and intuition of the chemist. 

The molecules of two organic compounds are sometimes composed of the same type and number of atoms, but arranged in different ways. The molecular formula of each one of such compounds, which are known as isomers (for example, isoleucine and alloisoleucine, shown in Fig. 73), is therefore identical to that of the other only the structural formulas of the two isomers show the differences between their molecules (see Textbox 63). 

FIGURE 60 Formulas of organic substances. The molecular formula of an organic substance conveys information about the nature of the component elements (expressed by symbols) and the number of atoms of each element that make up a molecule of the substance if greater than one, the number of atoms of each element is indicated by a subscript. The structural formula provides a two-dimensional representation of the arrangement of the atoms in the molecule, showing how they are attached to one another and the type of bonds involved. 

In this question consider organic molecule with no rings or carbon-to-carbon double or triple bonds, (a) Show that ethers can be isomers of alcohols but not of aldehydes, (ft) Show that aldehydes and ketones can be isomers of each other, but not of acids or alcohols, (c) Write the structural formula for an alcohol isomeric with diethyl ether. 

Determine the lowest energy transition of a simple organic molecule from the molar absorption coefficient and the structural formula. 

In organic chemistry, structural formulae are frequently presented as condensed formulae. This abbreviated presentation is especially useful for large molecules. Another way of presenting structural formulae is by using bonds only, with the understanding that carbon and hydrogen atoms are never explicitly shown. 

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