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Chapter 12 Alkanes

Chapter 12 Alkanes. 12.2 IUPAC Naming System for Alkanes 12.3 Drawing Structural Formulas. CH 3 CH 3 | | CH 3 — CH — CH 2 — CH — CH 3 2,4-dimethylpentane. Branched-Chain Alkanes.

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Chapter 12 Alkanes

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  1. Chapter 12 Alkanes 12.2 IUPAC Naming System for Alkanes 12.3 Drawing Structural Formulas CH3CH3 | | CH3—CH—CH2—CH—CH3 2,4-dimethylpentane

  2. Branched-Chain Alkanes • In a branched-chain alkane, a side group called a branch or a substituent is attached to a carbon chain. branch

  3. Classification of Carbon Atoms Carbon atoms are classified according to the number of attached carbon atoms. • Primary (1°) bonds to one carbon atom. • Secondary(2°) bonds to two carbon atoms. • Tertiary(3°) bonds to three carbon atoms. CH3 | CH3 —CH2—CH2—CH3 CH3—CH—CH3 secondaryprimary tertiary

  4. Alkyl Groups An alkyl group: • Is composed of one or more carbon atoms attached to a carbon chain. • Is derived from the corresponding alkane by removing one hydrogen. • Is named by replacing the –aneending of the corresponding alkane with –yl. • Derived from methane is methyl and from ethane is ethyl.

  5. Alkyl Groups

  6. Naming Branched-Chain Alkanes The names of branched-chain alkanes indicate the groups bonded to the longest carbon chain. CH3 methyl group on C-3 | CH3—CH2—CH2—CH—CH2—CH3 hexane 6 5 4 3 2 1 3-Methylhexane

  7. Naming Summary In the IUPAC system: • The longest chain is named as the main chain. • Any carbon branches use their alkyl names. • Each branch is numbered by counting the main chain from the end nearest the first side group. • Branches are listed in alphabetical order.

  8. What Is In A Name? The structural formula is drawn from the IUPAC name. 2, 4-dimethylhexane 2, 4 dimethyl hexane Location of Two CH3- groups 6 carbon main chain branches on attached with single C-C bonds main chain

  9. Drawing Structural Formulas Draw the condensed formula of 2-methylpentane 1. Draw the main chain of 5 carbon atoms. C—C—C—C—C 2. Add a CH3 branch to C-2 on the main chain. CH3 | C—C—C—C—C 3. Add hydrogen atoms to give 4 bonds to each C. CH3 | CH3—CH—CH2—CH2—CH3

  10. Writing Isomers The constitutional isomers for C4H10 can be written by first writing the continuous chain. Then remove one CH3 and attach it as a branch. CH3 | CH3—CH2—CH2—CH3 CH3—CH—CH3 Butane 2-Methylpropane

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