Summary and Key Words

All decisions involve tradeoffs. Does the benefit of a pesticide that will increase the availability of food outweigh the health risk to 1 person in 1 million who are exposed Do the beneficial effects of a new drug outweigh a potentially dangerous side effect in a small number of users The answers aren t always obvious, but it s the responsibility of legislators and well-informed citizens to keep their responses on a factual level rather than an emotional one. 

VVe afj take many risks each day, some much more dangerous than others. 

Kekule structure, 11 Lewis structure, 10 line-bond structure, 11 

Organic chemistry is the study of carbon compounds. Although a division into organic and inorganic chemistry occurred historically, there is no scientific reason for the division. 

Covalent bonds are formed when an electron pair is shared between atoms. According to valence bond theory, electron sharing occurs by overlap of two atomic orbitals. According to molecular orbital (MO) theory, bonds result from the combination of atomic orbitals to give molecular orbitals, which belong to the entire molecule. Bonds that have a circular cross-section and are formed by head-on interaction are called sigma (sr) bonds bonds formed by sideways interaction of p orbitals are called pi (n-) bonds. 

Organic molecules often have polar covalent bonds as a result of unsym-metrical electron sharing caused by differences in the electronegativity of atoms. For example, a carbon-chlorine bond is polar because chlorine attracts the shared electrons more strongly than carbon does. Carbon-hydrogen bonds are relatively nonpolar. Many molecules as a whole are also polar owing to the cumulative effects of individual polar bonds and electron lone pairs. The polarity of a molecule is measured by its dipole moment, p. 

Plus (+) and minus (-) signs are used to indicate the presence of formal charges on atoms in molecules. Assigning formal charges to specific atoms is a bookkeeping technique that makes it possible to keep track of the valence electrons around an atom. 

Some substances, such as nitromethane, benzene, and acetate ion, can t be represented by a single Lewis or line-bond structure and must be considered as a resonance hybrid of two or more structures, neither of which is correct by itself. The only difference between two resonance forms is in 

Organic molecules are usually drawn using either condensed structures or skeletal structures. In condensed structures, carbon-carbon and carbon-hydrogen bonds aren t shown. In skeletal structures, only the bonds and not the atoms are shown. A carbon atom is assumed to he at the ends and at the junctions oflines (bonds), and the correct number of hydrogens is mentally supplied. 

22 Convert each of the following models into a skeletal structure. Only the connections between atoms arc shown multiple bonds are not indicated (gray = C, red O, blue = N. ivory = H). 

A functional group is a group of atoms within a larger molecule that has a characteristic chemical reactivity. Because functional groups behave in approximately the same way in all molecules where they occur, the chemical reactions of an organic molecule are largely determined by its functional groups. 

Alkanes are a class of saturated hydrocarbons with the general formula C H2n. -2- They contain no functional groups, are relatively inert, and can be either straight-chain (normal) or branched. Alkanes are named by a series of IUPAC rules of nomenclature. Compounds that have the same chemical formula but different structures are called isomers. More specifically, compounds such as butane and isobutane, which differ in their connections between atoms, are called constitutional isomers. 

Carbon-carbon single bonds in alkanes are formed by a overlap of carbon sjy hybrid orbitals. Rotation is possible around a bonds because of their cylindrical 

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19 Identify the functional groups in the following substances, and convert each drawing into a molecular formula (red = O, blue = N)  

Online homework for this chapter may be assigned in Organic OWL. 

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