Structure formulas for organic compounds

Problem 8.39 Write a structural formula for organic compounds (A) through (N) ... 

Structural formulas for organic compounds are often written without the Lewis dots for unshared electrons. 

Why do chemists use structural formulas for organic compounds rather than molecular formulas such as... 

F. A. Kekuld s structural formulae for organic compounds ring. structure of benzene 1865. 

Structural formulas show how the atoms are connected together, their relative spatial orientations, and an indication of the distances between atoms and the angles between the bonds that connect atoms. Structure is the key to understanding properties of molecules, especially large molecules. Therefore, it is very common to write structural formulas for organic compounds instead of simple molecular formulas. 

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 ... 

The table shown here lists the molar heats of vaporization for several organic compounds. Use specific examples from this list to illustrate how the heal of vaporization varies with (a) molar mass, (b) molecular shape, (c) molecular polarity, (d) hydrogen-bonding interactions. Explain these comparisons in terms of the nature of the intermoiecuiar forces at work (You may find it helpful to draw out the structural formula for each compound.)... 

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. 

Hydrocarbons are organic compounds that consist of only carbon and hydrogen. In the simplest hydrocarbon, methane (CHt), the carbon atom forms an octet by sharing its four valence electrons with four hydrogen atoms. In organic molecules, every carbon atom has four bonds. A hydrocarbon is referred to as a saturated hydrocarbon when all the bonds in the molecule are single bonds. We can draw an expanded structural formula for a compound by showing all the bonds between atoms. 

Two-Dimensional Representation of Chemical Structures. The lUPAC standardization of organic nomenclature allows automatic translation of a chemical s name into its chemical stmcture, or, conversely, the naming of a compound based on its stmcture. The chemical formula for a compound can be translated into its stmcture once a set of semantic rules for representation are estabUshed (26). The semantic rules and their appHcation have been described (27,28). The inverse problem, generating correct names from chemical stmctures, has been addressed (28) and explored for the specific case of naming condensed benzenoid hydrocarbons (29,30). 

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