Lecture 6 Wednesday 1/25/17
THE SHAPE OF CYCLOALKANES
THE SHAPE OF CYCLOALKANES (continued)
NAMING CYCLOALKANES Cycloalkanes are alkanes containing rings of carbon atoms. The prefix __________- is used before the alkane name. When two or more substituents are attached to the cycloalkanes, the ring numbering begins with the first group alphabetically and proceeds to give lowest numbers possible. Example: CH2CH3 1 2 3 CH3
ISOMERISM & CYCLOALKANES Stereoisomers are compounds with the same structural formula but different spatial arrangements of atoms. Geometric isomers are molecules with restricted rotation around C-C bonds that differ in the three-dimensional arrangements of their atoms in space and not in the order of linkage of atoms. Rotation about C-C single bonds occurs in open-chain compounds but not within rings.
ISOMERISM & CYCLOALKANES (continued) Two geometric isomers exist for 1,2-dimethylcyclopentane. _______-substituents are on the _______ side of the ring. _______-substituents are on the ________ sides of the ring.
PHYSICAL PROPERTIES OF ALKANES Non-polar molecules with weak intermolecular forces Not soluble in water Low density (less dense than water) Melting points increase with molecular size Boiling points increase with molecular size
PHYSICAL PROPERTIES OF ALKANES (continued) A homologous series is a group of compounds with the same functional class that differ by a –CH2– group.
PHYSICAL PROPERTIES OF ALKANES (continued)
ALKANE REACTIONS Alkanes are the least reactive of all organic compounds. The most significant reaction of alkanes is combustion (rapid oxidation). Many alkanes are used as fuels. Methane – natural gas Propane – used in gas grills Butane – lighters Gasoline – a mixture of hydrocarbons
ALKANE REACTIONS (continued) Complete Combustion (in the presence of adequate oxygen) Incomplete Combustion (not enough oxygen available) CH4 + 2O2 → CO2 + 2H2O + 212.8 kcal/mol 2CH4 + 3O2 → 2CO + 4H2O CH4 + O2 → C + 2H2O
Chapter 12 unsaturated hydrocarbons
UNSATURATED HYDROCARBONS Unsaturated hydrocarbons contain one or more carbon-carbon multiple bonds. ______________ contain one or more carbon-carbon double bonds _____________ contain one or more carbon-carbon triple bonds _________ contain benzene rings.
NAMING ALKENES Step 1: Name the longest chain that contains the C=C bond. Use the IUPAC root and the –ene ending. Step 2: Number the longest chain so the carbon atoms joined in the C=C bond get the lowest number possible. Step 3: Locate the C=C bond with the lower-numbered carbon. Examples: CH3-CH=CH-CH3 CH3-CH2-CH2-CH=CH-CH3
NAMING ALKENES (continued) Step 4: Locate and name attached groups. Step 5: Combine all the names.
NAMING ALKENES WITH MULTIPLE DOUBLE BONDS Step 1: Follow the same naming instructions for alkenes with one double bond, except use the endings –diene, – triene, and the like to denote the number of double bonds. Step 2: Indicate the location of all the multiple bonds. EXAMPLES:
BONDING CHARACTERISTICS ALKANES
THE GEOMETRY OF ALKENES In C=C bonds, sp2 hybrid orbitals are formed by the carbon atoms, with one electron left in a 2p orbital. A representation of sp2 hybridization of carbon:
THE GEOMETRY OF ALKENES (continued) During hybridization, two of the 2p orbitals mix with the single 2s orbital to produce three sp2 hybrid orbitals. One 2p orbital is not hybridized and remains unchanged.
THE GEOMETRY OF ALKENES (continued) This gives a planar shape for the sp2 bonding orbitals with the unhybridized p orbital perpendicular to the plane of the three sp2 hybridized orbitals.
THE GEOMETRY OF ALKENES (continued)
THE GEOMETRY OF ALKENES (continued) Because there is no free rotation about the C=C bond, _________________________ is possible. _______________________ have two similar or identical groups on the same side of the double bond. _______________________ have two similar or identical groups on opposite sides of the double bond.
THE GEOMETRY OF ALKENES (continued) Geometric isomers have different physical properties.
PHYSICAL PROPERTIES OF ALKENES
PHYSICAL PROPERTIES OF ALKENES