Chapter 21: Hydrocarbons Section 21.3 Alkenes and Alkynes

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1 Section 21.1 Introduction to Hydrocarbons Section 1 Objectives: Explain the terms organic compound and organic chemistry. Section 21.2 Alkanes Chapter 21: Hydrocarbons Section 21.3 Alkenes and Alkynes Identify hydrocarbons and the models used to represent them. Section 21.4 Hydrocarbon Isomers Distinguish between saturated and unsaturated hydrocarbons. Section 21.5 Aromatic Hydrocarbons Describe where hydrocarbons are obtained and how they are separated. Organic Compounds Chemists in the early 19th century knew living things produced a variety of carbon compounds, called compounds. They were not able to in the lab and labeled them as mysterious. was the first to produce an organic compound in the lab. is applied to all -containing compounds with the primary exceptions of carbon oxides, carbides, and carbonates, which are considered inorganic. In organic compounds, carbon nearly always shares its electrons and forms. Carbon atoms are bonded to hydrogen atoms or other elements near carbon on the periodic table. Carbon atoms also bond to other carbon atoms and form Hydrocarbons The simplest organic compounds are, which consist of only the elements. There are thousands of hydrocarbons. Models of Methane Carbon atoms bond to each other by bonds. hydrocarbons contain only single bonds. hydrocarbons contain at least one double or triple bond. Refining Hydrocarbons Many hydrocarbons are obtained from the Petroleum, crude oil, is a complex mixture containing more than a thousand different compounds. In its raw form it is not very useful to humans, it is more useful when separated into or involves boiling petroleum and collecting each group of components as they condense at different temperatures. Fractional distillation towers do not yield fractions in Heavier fractions are converted to gasoline or other lighter fractions by a process called cracking is done in the absence of oxygen and in the presence of a catalyst. In addition to converting heavier fractions to gasoline, cracking also produces starting materials for the synthesis of many different products including plastics, films and synthetic fibers. is not a pure substance. Most molecules have carbons. Gasoline is modified by adjusting its composition to improve performance, resulting in the. Section 2 Objectives: Name alkanes by examining their structures. Draw the structure of an alkane when given its name. Describe the properties of alkanes. Straight-Chain Alkanes are hydrocarbons that have only single bonds between atoms. The names of alkanes end in Prefixes are derived from Table 21.1-Simple Alkanes Molecular Formula Ethane (C 2H 6) Propane (C 2H 6) Butane (C 2H 6) Structural Formula

2 A series of compounds that differ from one another by a repeating unit is called a. For alkanes, the relationship between the numbers of carbon and hydrogen atoms can be expressed as: Branched-Chain Alkanes Carbon atoms can bond to other carbon atoms making a variety of chains possible. Straight chains and can have the same molecular formula. Order and arrangement of atoms in organic compounds determine When naming branched chain alkanes, the longest continuous chain of carbon atoms is called the All the side branches are known as Table 21.2 First Ten of Alkane Series Name Molecular Formula Condensed Structural Formula CH 4 C 2H 6 CH 3CH 3 C 3H 8 C 4H 10 C 5H 12 CH 3CH 2CH 2CH 2CH 3 C 6H 14 C 7H 16 CH 3CH 2CH 2CH 2CH 2CH 2CH 3 C 8H 18 C 9H 20 C 10H 22 CH 3(CH 2) 8CH 3 Naming branched-chain alkanes Count the number of carbon atoms in the chain. Table 21.3 Common Alkyl Groups Name Condensed Structural Formula CH 3- CH 3CH 2- CH 3CH 2CH 2- CH 3CHCH 3 CH 3CH 2CH 2CH 2- Structural Formula Number each carbon in the parent chain, starting with the to the substituent group. This gives all the substituent groups the Name each alkyl group If the same alkyl group appears as a branch on the parent structure, use a to indicate how many times it appears. When different alkyl groups are attached to the same parent chain, place their names in Write the entire name, using to separate numbers from words and commas to separate numbers. Cycloalkanes An organic compound that contains a hydrocarbon ring is called a. Cyclic hydrocarbons with only single bonds are called. The relationship between numbers of carbon and hydrogen atoms in cycloalkanes can be expressed as: Naming substituted cycloalkanes is the same as but with a few exceptions. The is always considered the parent chain. Numbering starts on the carbon that is When more than one carbon has a substituent, number in the that gives the for the substituents. Properties of Alkanes Structure affects. Alkanes are and are good solvents for other nonpolar molecules. Physical properties of alkanes: Compared to water, methane boils and melts at. Methane molecules have little intermolecular attraction compared to water. (Methane molecules are nonpolar and do not form hydrogen bonds). Chemical properties of alkanes: Alkanes have because they are nonpolar and have no charge, and because they have strong single bonds between carbon atoms.

3 Section 3 Objectives: Compare the properties of alkenes and alkynes with those of alkanes. Describe the molecular structures of alkenes and alkynes. Name an alkene or alkyne by examining its structure. Alkenes Unsaturated hydrocarbons that contain at least one or more double covalent bonds between carbon atoms are called. Draw the structure of an alkene or alkyne by analyzing its name. Alkenes are named in much the same way as alkanes. Alkenes end in When four or more carbon atoms are present, of the double bond. Note: Structure 3 is not 3-Butene because it is identical to structure 1. When naming branched-chain alkenes, follow the, with two exceptions. The parent chain is always the, whether it is the longest chain or not. The position of the, not the, determine the numbering. Use a prefix to designate the number of double bonds. Alkenes are nonpolar and have low solubility in water. Alkenes are than alkanes because the double bond increases electron density between the two carbon atoms, providing a good site for Alkynes Unsaturated hydrocarbons that contain one or more triple bonds between carbon atoms are called. Straight-chain and branched-chain alkynes are named in the same way as alkenes, except the ending is. Alkynes have physical and chemical properties similar to alkenes but are generally more reactive because the triple bonds cause even than double bonds. Section 4 Objectives: Distinguish between the two main categories of isomers structural isomers and stereoisomers. Differentiate between geometric isomers with cis- and trans-prefixes. Describe the structural variation in molecules that results in optical isomers. Structural Isomers are two or more compounds that have the same molecular formula but different molecular structures. have the same chemical formula but their atoms are bonded in different arrangements. There are two main classes of isomers: structural isomers and. Structural isomers have different physical and chemical properties. The of a substance determines properties. are isomers in which all atoms are bonded in the same order but are arranged differently in space.

4 result from different arrangements of groups around a double bond. means on the same side, and means across from. Geometric isomers have different and. Chirality discovered two forms of crystallized tartaric acid. The forms were mirror images of each other called The property in which a molecule exists in right and left-handed forms is called Chirality occurs whenever a compound contains an asymmetric carbon. is a carbon atom that has four different atoms or groups attached to it. The four groups can be arranged in Isomers that result from different arrangements of four different groups around a carbon atom represent the other class of stereoisomers, called. Optical isomers have the same physical and chemical properties except in where is important. When polarized light passes through a solution containing an optical isomer, the plane of polarization is rotated to the and to the, producing and effect called

5 Section 5 Objectives: Compare and contrast the properties of aromatic and aliphatic hydrocarbons. Explain what a carcinogen is, and list some examples. The Structure of Benzene Even by the middle of the 19th century, Michael Faraday first isolated in Chemists knew the formula was and proposed several possible models which would have all be very reactive, but benzene is German chemist Friederich Kekulé claimed to have had a in which he realized the structure for benzene. Kekulé s structure explained some of benzene's properties, but not its. Linus Pauling s explained benzene s lack of reactivity. The double bonds in benzene are, but rather the electrons are and shared among atoms. Aromatic Compounds Organic compounds that contain benzene rings as part of their structure are called Aromatic was originally used because many benzene related compounds were found in that came from plants and plant parts. are the alkane, alkene, and alkyne hydrocarbons, coming from the Greek word for because they were obtained by heating Substituted benzene compounds are named in the same way as Many aromatic compounds were commonly used as Health risks linked to aromatics include. Some aromatic compounds cause and are called