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Topic : Alkanes

Topic : Alkanes. Do Now: Draw the possible bonds a single carbon atom can have if it has a bonding capacity of 4. Alkanes. Homologous series of saturated hydrocarbons Release energy when burned C n H 2n+ 2 – all have this general formula CH 4 H

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Topic : Alkanes

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  1. Topic: Alkanes Do Now: Draw the possible bonds a single carbon atom can have if it has a bonding capacity of 4

  2. Alkanes • Homologous series of saturated hydrocarbons • Release energy when burned • CnH2n+2 – all have this general formula CH4 H H–C–H H C2H6 H H H–C–C–H H H

  3. Saturatedhydrocarbons: organic compounds containing only Single bonds – can’t add any more Hydrogens

  4. Properties of Alkanes • Low Reactivity • Except readily undergo combustion (fuels) • Nonpolar – don’t dissolve well in water • Low melting & low boiling points • both increase with molecular mass • High vapor pressures

  5. Properties of Alkanes • Change systematically with # of C’s • As # of C’s increases, boiling point increases • molecules get heavier so harder to change into gas phase

  6. Which property is generally characteristic of an organic compound? • Low melting point • High melting point • Soluble in polar solvents • Insoluble in nonpolar solvents Correct response = A

  7. Which of the following compounds has the highest boiling point? • CH4 • C2H6 • C3H8 • C4H10 Correct answer = D nonpolar covalcmpd: • bp depends on strength of van der Waals interactions • van der Waals forces ↑ as size of molecule ↑ • bigger molecule = bigger electron cloud

  8. Alkanes (CnH2n+2) C3H8 H H H H–C–C–C–H H H H CH3CH2CH3 Chemical Formula Structural Formula Condensed Structural Formula

  9. straight-chain alkane C4H10 H H H H H–C–C–C–C–H H H H H Or CH3CH2CH2CH3

  10. Naming straight-chain Alkanes • Name: describes molecule so can draw it • all alkanes have the suffix –ane • prefix: tells # of C’s

  11. Prefix # of C atoms Meth 1 Formula Name Eth 2 CH4 Meth + ane Prop 3 But 4 C2H6 Pent 5 C3H8 Propane Hex 6 C4H10 Hept 7 Butane Oct 8 C5H12 Pentane Non 9 Dec 10 Ethane

  12. Naming Branched-Chain Alkanes • goal of name is to describe molecule so you can draw it

  13. Naming branched-chain alkanes • Find longest continuous chain of C atoms - Bends don’t matter!

  14. 2. base name derived from # C’s in continuous chain 9 carbon chain = nonane

  15. 3. Branches named first and in alphabetical order * to name branches, count # C atoms & add “yl” to prefix name * If more than one of same type of branch - use di, tri, etc. propyl ethyl ethyl methyl ethyl triethyl, methyl, propyl

  16. Assign number to Branches based on longest carbon chain * you want numbers to add up to the lowest # propyl ethyl 3 6 ethyl 4 5 7 2 8 methyl 1 9 ethyl 4, 4, 5, 5, 6 = add up = 24

  17. Assign number to Branches based on longest carbon chain * you want numbers to add up to the lowest # propyl ethyl 6 7 ethyl 5 4 3 8 2 methyl 9 1 ethyl 4, 5, 5, 6, 6 = add up = 26

  18. 4,4,6-triethyl 5-methyl 5-propyl nonane 4. Put it all together propyl ethyl 3 6 ethyl 4 5 7 2 1. nonane 8 methyl 1 2. triethyl, methyl, propyl 9 ethyl 3. 4, 4, 5, 5, 6

  19. H H–C–H H H H–C–C–C–H H H H 2-methyl propane No because if methyl was anywhere else it wouldn’t be propane 2 1 3 Methyl propane C4H10 CH3CH(CH3)CH3 Longest continuous chain has 3 carbon atoms – propane

  20. Longest continuous chain has 5 C atoms: pentane Branch: 1 carbon =methyl Branch: 12 carbon =ethyl Branch located at C-2 and 3 3-ethly 2-methyl pentane C8H18 CH3CH(CH3) CH(CH2CH3)CH2CH3 H H–C–H H–C–H H H H H–C–C–C–C–H H H H H–C–H H 6 5 4 3 2 1

  21. Branched-chain alkanes Beginning with butane, C4H10, there is more than 1 way to arrange the atoms H H–C–H H H H–C–C–C–H H H H ISOMERS

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