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Properties of Alkanes Long, unbranched alkanes tend to have higher melting points, boiling points, and enthalpies of vap

Properties of Alkanes Long, unbranched alkanes tend to have higher melting points, boiling points, and enthalpies of vaporization than their branched isomers. Cycloalkanes : ring alkanes; made up of CH 2 groups General formula: C n H 2n. cyclohexane. “boat”. “chair”.

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Properties of Alkanes Long, unbranched alkanes tend to have higher melting points, boiling points, and enthalpies of vap

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  1. Properties of Alkanes Long, unbranched alkanes tend to have higher melting points, boiling points, and enthalpies of vaporization than their branched isomers

  2. Cycloalkanes: ring alkanes; made up of CH2 groups General formula: CnH2n

  3. cyclohexane “boat” “chair”

  4. Unsaturated Aliphatic Hydrocarbons Alkenes: carbon-carbon double bond (sp2 hybridized) Alkynes: carbon-carbon triple bond (sp hybridized) CHCH (acetylene) CH2=CH2 (ethylene)

  5. IUPAC Nomenclature for Aliphatic Hydrocarbons Straight-chain alkanes - name ends in -ane Branched alkane - side chain is a “substituent”  name the substituent formed by the removal of one H atom from an alkane by changing the ending from -ane to -yl  name of the alkane is derived from the longest continuous carbon chain  to indicate the position of the substituent, the C atoms in the longest chain are numbered, starting at the end that will give the lowest number for the position of the first attached group

  6.  use prefixes di-, tri-, tetra-, penta-, etc. to indicate the number  substituents are listed in alphabetical order (disregard the prefix) 2,2,4-trimethylpentane 2-ethyl-1,1-dimethylcyclohexane (sum of the numbers is lowest)

  7. Alkenes and Alkynes Double bonds - change the “ane” suffix to “ene” Triple bonds - change the “ane” to “yne” Position of the multiple bond is given by the number of the first C atom in the multiple bond CH3-CH2-CH=CH-CH3 2-pentene CH3-CH2-CH2-CCH3 1-pentyne CH2=CH-CH=CH2 1,3-butadiene

  8. Reactions of Alkanes Alkanes are not very reactive Strong C-C and C-H bonds mean bond enthalpy (kJ/mol) C-C 348 C-H 412 1) Oxidation Reactions CH4(g) + 2 O2(g)  CO2(g) + 2H2O(g) DHo = -890 kJ Break the strong C-H bond, but replaced by two C=O bonds (mean bond enthalpy of C=O is 743 kJ/mol). Also O-H bond is strong (463 kJ/mol)

  9. light or heat CH4(g) + Cl2(g) CH3Cl(g) + HCl(g) light or heat Cl-Cl 2 Cl initiation step 2) Substitution Reactions Cl + CH4 CH3 + HCl propagation steps CH3+ Cl2 CH3Cl+ Cl Cl + Cl Cl2 termination steps CH3+ CH3 CH3CH3 CH3+ Cl CH3Cl

  10. catalyst CH3CH3(g) CH2=CH2(g) + H2(g) Alkenes Prepration - Elimination Reactions 1) From alkanes by dehyrogenation 2) From haloalkanes - dehydrohalogenation CH3CH2Cl + KOH  CH2=CH2 + KCl + H2O 3) Dehydration of alcohols H2SO4 CH3CH2OH CH2=CH2(g) + H2O http://www.whfreeman.com/chemicalprinciples/con_index.htm?18

  11. Reactions 1) Addition reactions Double bonds are more reactive than single bonds http://www.whfreeman.com/chemicalprinciples/con_index.htm?18

  12. 1-chloropropane 2-chloropropane 2-chloropropane is the product The H atom always goes to the C atom of the double bond that already has the most H atoms - Markovnikov addition

  13. 1-propanol Markovnikov’s rule holds - 2-propanol is favored 2-propanol

  14. catalyst Polymerization reactions n CH2=CH2 -[CH2-CH2]-n cis geometry

  15. trans-geometry

  16. Aromatic Hydrocarbons Parent compound of aromatic hydrocarbons - benzene (C6H6) C is sp2 hybridized, ring is planar As a substituent - phenyl (C6H5)

  17. Phenol (C6H5OH) Toluene 2,4,6-trinitrotoluene (TNT)

  18. Resonance Stablization p-bonding electrons are delocalized over all C atoms Resonance imparts stability to benzene with respect to hydrogenation and oxidation

  19. Addition (Br2) none rapid none

  20. Substitution Reactions - p-bonds in the ring are left intact; substituent replaces an H atom

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