Organic Chemistry The Shape of Molecules

We turn now to another area of chemistry where imtil recently, the notion of shape has been ignored. Organic molecules are constructed from three basic 3 2 

If we start with the simplest possible case, aliphatic hydrocarbons, we can 

In a small molecule it is usually difficult to perceive the saddle surface. This is most certainly due to the conditioning provided by various educational agencies students are led to believe that the H-C-H angle in, e.g. methane is 

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STRUCTURAL ORGANIC CHEMISTRY. THE SHAPES OF MOLECULES. FUNCTIONAL GROUPS... 

Structural Organic Chemistry. The Shapes of Molecules. Functional Groups... 

Alkenes are hydrocarbons that contain a carbon-carbon double bond A carbon-carbon double bond is both an important structural unit and an important func tional group m organic chemistry The shape of an organic molecule is influenced by the presence of this bond and the double bond is the site of most of the chemical reactions that alkenes undergo Some representative alkenes include isobutylene (an industrial chemical) a pmene (a fragrant liquid obtained from pine trees) md fame sene (a naturally occurring alkene with three double bonds)... 

Most students in organic chemistry find that buiiding models helps them visualize the shape of molecules. Invest in a set of models now. 

The picture of molecules being composed of structural units, functional groups , which behave similarly in different molecules forms the very basis of organic chemistry. The drawing of molecular structures where alphabetic letters represent atoms and lines represent bonds is used universally. Organic chemists often build ball and stick, or CPK space-filling, models of their molecules to examine their shapes Force, field methods are... 

The first quantum chemical theory to give a convincing explanation of the shapes of molecules was the concept of hybrid orbitals. This is best illustrated by using carbon as an example, and is appropriate since the language of hybridization is still commonly used in organic chemistry. 

Chapters 1—10 begin a study of organic compounds by first reviewing the fundamentals of covalent bonding, the shapes of molecules, and acid-base chemistry. The structures and typical reactions of several important classes of organic compounds are then discussed alkanes, alkenes and alkynes, haloalkanes, alcohols and ethers, benzene and its derivatives, and amines, aldehydes, and ketones, and finally carboxylic acids and their derivatives. 

In chemistry the similarity of molecules plays a central role. Indeed, comparable molecules, usually molecules with a similar shape, are expected to show similar chemical properties and reactivity patterns. Specifically, there chemical behavior is expected to be similar [34]. The concept of functional groups is extensively used in organic chemistry [35], through which certain properties are transferable (to a certain extent) from one molecule to another, and the intense QSAR investigations in pharmaceutical chemistry [36] are illustrations of the attempts to master and exploit similarity in structure, physicochemical properties and reactivity of molecular systems. 

The division of the molecular volume into atomic basins follows from a deeper analysis based on the principle of stationary action. The shapes of the atomic basins, and the associated electron densities, in a functional group are very similar in different molecules. The local properties of the wave function are therefore transferable to a very good approximation, which rationalizes the basis for organic chemistry, that functional groups react similarly in different molecules. It may be shown that any observable... 

The present activity in the field reflects the unique capabilities available with dendrimers Basically the whole world of chemistry can be conceived as a dendritic molecule in the shape of almost any molecular building blocks of organic, inorganic or biochemical origin. Practically every chemist should be able to enter the field of dendrimer chemistry or take advantage of it for his specific needs. 

As you observed in the ExpressLab, the shape of a molecule depends on the type of bond. Table 1.1 describes some shapes that you must know for your study of organic chemistry. In Unit 2, you will learn more about why different shapes and angles form around an atom. 

Line structures also can be modified to represent the three-dimensional shapes of molecules, and the way that this is done will be discussed in detail in Chapter 5. At the onset of your study of organic chemistry, you should write out the formulas rather completely until you are thoroughly familiar with what these abbreviations stand for. 

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