11.S: Organic Chemistry (Summary)

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To ensure that you understand the material in this chapter, you should review the meanings of the following bold terms in the summary and ask yourself how they relate to the topics in the chapter.

Organic chemistry is the chemistry of carbon compounds, and inorganic chemistry is the chemistry of all the other elements. Carbon atoms can form stable covalent bonds with other carbon atoms and with atoms of other elements, and this property allows the formation the tens of millions of organic compounds. Hydrocarbons contain only hydrogen and carbon atoms.

Hydrocarbons in which each carbon atom is bonded to four other atoms are called alkanes or saturated hydrocarbons. They have the general formula C_nH₂_n _{+ 2}. Any given alkane differs from the next one in a series by a CH₂ unit. Any family of compounds in which adjacent members differ from each other by a definite factor is called a homologous series.

Carbon atoms in alkanes can form straight chains or branched chains. Two or more compounds having the same molecular formula but different structural formulas are isomers of each other. There are no isomeric forms for the three smallest alkanes; beginning with C₄H₁₀, all other alkanes have isomeric forms.

A structural formula shows all the carbon and hydrogen atoms and how they are attached to one another. A condensed structural formula shows the hydrogen atoms right next to the carbon atoms to which they are attached. A line-angle formula is a formula in which carbon atoms are implied at the corners and ends of lines. Each carbon atom is understood to be attached to enough hydrogen atoms to give each carbon atom four bonds.

Cycloalkanes are saturated hydrocarbons whose molecules are closed rings rather than straight or branched chains. Rings restrict rotation, so if there are two non-hydrogen substituents on different carbons of a cyclohexane, two cis-trans isomers (or geometric isomers) can exist.

Any hydrocarbon containing either a double or triple bond is an unsaturated hydrocarbon. Alkenes have a carbon-to-carbon double bond. The general formula for alkenes with one double bond is C_nH₂_n. Double bonds cannot rotate so if there is one non-hydrogen substituent on each of the double-bonded carbons, two cis-trans isomers can exist. Alkynes have a carbon-to-carbon triple bond. The general formula for alkynes is C_nH₂_n _{− 2}.

The physical properties of hydrocarbons reflect the fact that the molecules are nonpolar. Hydrocarbons are insoluble in water and less dense than water. Size and presence of polar functional groups can affect the water solubility, melting point, and boiling point of organic compounds. The IUPAC System of Nomenclature provides rules for naming organic compounds. An alkyl group is a unit formed by removing one hydrogen atom from an alkane.

A functional group is any atom or atom group that confers characteristic properties to a family of compounds. Alkanes are generally unreactive toward laboratory acids, bases, oxidizing agents, and reducing agents; they do burn in oxygen (undergo combustion reactions). Alkenes and alkynes are more reactive, susceptible to addition by halogens or water, for example. Carboxyl functional groups are weak acids and amine functional groups are weak bases.