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Chemistry 30

Chemistry 30. Chapter 9. Naming Alkanes. Alkanes Hydrocarbons whose empirically determined molecular formulas indicate that the carbon-carbon bonds are only single bonds Simplest structural alkane is methane CH 4.

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Chemistry 30

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  1. Chemistry 30 Chapter 9

  2. Naming Alkanes • Alkanes • Hydrocarbons whose empirically determined molecular formulas indicate that the carbon-carbon bonds are only single bonds • Simplest structural alkane is methane CH4

  3. Each formula in the series has has one more CH2 group than the one proceeding it. • The general molecular formula for an alkane is CnH(2n+2) • A series of CH2 units plus two terminal hydrogen atoms

  4. Alkanes are… • Homologous Series • A sequence of molecules with similar structure and differing only the number of repeated units • Saturated Hydrocarbons • Compounds of carbon and hydrogen containing only carbon-carbon single bonds with the maximum number of hydrogen atoms bond to each carbon

  5. Alkanes

  6. Structural Isomers • There are several structures that can have the same molecular formula • Compounds with the same molecular formula, but with different structures, are called structural isomers

  7. Structural Isomers • Example: C4H10 • So, while we can say that butane always has the formula, C4H10, we cannot say that a compound with the formula C4H10 is always butane

  8. Structural Isomers • As the number of carbon atoms in a hydrocarbon increases, the number of possible isomers increases dramatically. • For Example • C10H22 has 75 possible isomers • C20H42 has 366 319 possible isomers • C30H62 has 4 111 846 763 possible isomers

  9. Names and Structures of Branched Alkanes • The name of a compound indicates whether there are branches on a carbon chain. • A BRANCH is any group of atoms that is not part of the main structure of the molecule.

  10. Structural Isomers • Consider the 3 isomers of C5H12 below • The unbranched isomer on the left is named pentane • Each of the 3 isomers have different physical and chemical properties

  11. Alkyl Branch • A branch consisting of only a single bonded carbon hydrogen atoms • In the names of alkyl branches, the prefixes are followed by a -yl suffix

  12. A “straight” chain description of C5H12

  13. A continuous chain of 4 carbon atoms with a methyl group on the second carbon atom • To name this structure, identify the parent chain – The longest continuous chain of carbon atoms • Here the 4 carbon carbons indicate that the parent chain is butane • Since a methyl group is added as a branch to the longest continuous chain of 4 atoms, this isomer is called methylbutane

  14. Two methyl groups are attached to the three-carbon (propane) parent chain • This third isomer is named dimehtylpropane

  15. Since there is only one methylbutane isomer and only one dumethylpropane isomer, we usually do not use numbers in the names of these molecules. • 2-methylbutane and 2,2-dimethylpropane are acceptable, but not neccesary • In most cases however, we need to number to carbon atoms to indicate the position(s) of the branch(es) (substitution groups)

  16. Write the name of the alkane, list the branches in alphabetical order, ignoring for example, the di and tri prefixes.

  17. Cycloalkanes • On the evidence of empirical formulas and chemical properties, chemists believe that organic carbon compounds sometimes take the form of cyclic hydrocarbons – hydrocarbons with a closed ring. • When al the carbon-carbon bonds in a cyclic hydrocarbon are single bonds, the compound is called a cycloalkane (CnH2n)

  18. Cycloalkanes

  19. Naming Cycloalkanes • Cycloalkanes are named by placing the prefix cyclo in front of the alkane name • cylcopropane • cyclobutane • If branches are present, treat the cycloalkane as the parent chain and identify the branches. Since there is no end at which to start the numbering for the location of the branches, use the lowest possible numbers. • Start with the location of one of the branches • Omit the 1 if only 1 branch is present

  20. Cycloalkanes

  21. Line Structure Formulas • Line structure formulas of hydrocarbons show the position of the carbon atoms as the intersections and ends of bonding lines; they do not show hydrogen atoms

  22. Unsaturated Hydrocarbons • Unsaturated Hydrocarbons • Organic compounds with carbon-carbon double or triple bonds • Have fewer hydrogen atoms than compounds with single carbon-carbon bonds • Unsaturated hydrocarbons can react readily with small diatomic molecules, such as hydrogen.

  23. Unsaturated Hydrocarbons • This type of reaction is an addition reaction • Addition of a sufficient quantity of hydrogen, called hydrogenation, converts unsaturated hydrocarbons to saturated ones

  24. Alkenes • Hydrocarbons with carbon-carbon double bonds are members of the Alkene family • They have a general formula of CnH2n • The names of alkenes with one double bond have the same prefixes as the names of alkanes, together with the ending -ene

  25. Alkynes • The alkyne family has chemical properties that can be explained only by the presence of a triple bond between carbon atoms • Alkynes are named like alkenes, except for the –yne ending • Empirical studies indicate that all alkynes with one triple bond have the general formula CnH2n-2

  26. Alkene and Alkyne Isomers • Isomers exist for all alkenes larger than propene and for all alkynes larger than propyne • Cycloalkanes are isomers of alkenes • Cylcoalkenes are isomers of alkynes

  27. Naming Alkenes and Alkynes • Alkenes and Alkynes are named much like alkanes, with two additional points to consider • The longest or parent chain of carbon atoms must contain the multiple bond, and the chain is numbered from the end closest to the multiple bond • The number that indicates the position of the multiple bond on the parent chain proceeds the ending (-ene or –yne) of the parent chain

  28. Example • There are two possible butene isomers • but-1-ene • but-2-ene

  29. Note that the number in front of the ending specifies the location of the multiple bond, just as the number in front of the branch indicates its location • Example • Parent chain is a pentyne

  30. When numbering the carbon atoms of an alkene or alkyne parent chain, chemists give more importance to the location of the multiple bond(s) than to the location of any branches (alkyl groups)

  31. Drawing Structural Formulas of Alkenes and Alkynes • Whenever you need to draw a structural formula for any hydrocarbon, first look at the end of the name to find the parent chain • Draw the parent Alkene or Alkyne first, and add the branches listed in the name • Be sure to finish the formula with sufficient hydrogen atoms to complete four bonds for each carbon atom

  32. Cycloalkenes and Cycloalkynes • Cycloalkenes • Its molecules have a circle of carbon atoms with at least one double bond • The structural formulas and names of cycloalkenes follow the same IUPAC rules as those for cycloalkanes.

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