Properties of Alkanes Long unbranched alkanes tend to
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: Cn. H 2 n
cyclohexane “boat” “chair”
Unsaturated Aliphatic Hydrocarbons Alkenes: carbon-carbon double bond (sp 2 hybridized) Alkynes: carbon-carbon triple bond (sp hybridized) CH CH CH 2=CH 2 (ethylene) (acetylene)
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
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)
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 CH 3 -CH 2 -CH=CH-CH 3 2 -pentene CH 3 -CH 2 -C CH 3 1 -pentyne CH 2=CH-CH=CH 2 1, 3 -butadiene
Reactions of Alkanes are not very reactive Strong C-C and C-H bonds mean bond enthalpy (k. J/mol) C-C 348 C-H 412 1) Oxidation Reactions CH 4(g) + 2 O 2(g) CO 2(g) + 2 H 2 O(g) DHo = -890 k. J Break the strong C-H bond, but replaced by two C=O bonds (mean bond enthalpy of C=O is 743 k. J/mol). Also O-H bond is strong (463 k. J/mol)
2) Substitution Reactions CH 4(g) + Cl 2(g) Cl-Cl light or heat 2 Cl + CH 4 CH 3 + HCl CH 3 Cl(g) + HCl(g) initiation step propagation steps CH 3 + Cl 2 CH 3 Cl + Cl Cl 2 CH 3 + CH 3 CH 3 + Cl CH 3 Cl termination steps
Alkenes Prepration - Elimination Reactions 1) From alkanes by dehyrogenation CH 3(g) catalyst CH 2=CH 2(g) + H 2(g) 2) From haloalkanes - dehydrohalogenation CH 3 CH 2 Cl + KOH CH 2=CH 2 + KCl + H 2 O 3) Dehydration of alcohols CH 3 CH 2 OH H 2 SO 4 CH 2=CH 2(g) + H 2 O http: //www. whfreeman. com/chemicalprinciples/con_index. htm? 18
Reactions 1) Addition reactions Double bonds are more reactive than single bonds http: //www. whfreeman. com/chemicalprinciples/con_index. htm? 18
1 -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
1 -propanol 2 -propanol Markovnikov’s rule holds - 2 -propanol is favored
Polymerization reactions n CH 2=CH 2 catalyst -[CH 2 -CH 2]-n cis geometry
trans-geometry
Aromatic Hydrocarbons Parent compound of aromatic hydrocarbons - benzene (C 6 H 6) C is sp 2 hybridized, ring is planar As a substituent - phenyl (C 6 H 5)
Phenol (C 6 H 5 OH) Toluene 2, 4, 6 -trinitrotoluene (TNT)
Resonance Stablization p-bonding electrons are delocalized over all C atoms Resonance imparts stability to benzene with respect to hydrogenation and oxidation
Addition (Br 2) none rapid none
Substitution Reactions - p-bonds in the ring are left intact; substituent replaces an H atom
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