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”

Unsaturated Aliphatic Hydrocarbons Alkenes: carbon-carbon double bond (sp 2 hybridized) Alkynes: carbon-carbon triple bond (sp hybridized) CH 2 =CH 2 (ethylene) CH  CH (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 (sum of the numbers is lowest) 2-ethyl-1,1-dimethylcyclohexane

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 -CH 2 -C  CH 3 1-pentyne CH 2 =CH-CH=CH 2 1,3-butadiene

Reactions of Alkanes Alkanes are not very reactive Strong C-C and C-H bonds mean bond enthalpy (kJ/mol) C-C348 C-H412 1) Oxidation Reactions CH 4 (g) + 2 O 2 (g)  CO 2 (g) + 2H 2 O(g)  H o = -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)

2) Substitution Reactions CH 4 (g) + Cl 2 (g) CH 3 Cl(g) + HCl(g) light or heat Cl-Cl 2 Cl  initiation step light or heat Cl  + CH 4  CH 3  + HClpropagation steps CH 3  + Cl 2  CH 3 Cl + Cl  Cl  + Cl   Cl 2 termination steps CH 3  + CH 3   CH 3 CH 3 CH 3  + Cl   CH 3 Cl

Alkenes Prepration - Elimination Reactions 1) From alkanes by dehyrogenation CH 3 CH 3 (g) CH 2 =CH 2 (g) + H 2 (g) catalyst 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 CH 2 =CH 2 (g) + H 2 O H 2 SO 4

Reactions 1) Addition reactions Double bonds are more reactive than single bonds

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-chloropropane 2-chloropropane

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

Polymerization reactions n CH 2 =CH 2 -[CH 2 -CH 2 ]-n catalyst 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  -bonding electrons are delocalized over all C atoms Resonance imparts stability to benzene with respect to hydrogenation and oxidation

Addition (Br 2 )nonerapidnone

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