unsaturated hydrocarbons double and triple bonds between carbons
Post on 28-Dec-2015
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Objectives
To distinguish between the unsaturated hydrocarbons called alkenes and alkynes and recognize how they differ from alkanes
To draw structural diagrams and write structural formulae of alkenes and alkynes
To name unsaturated hydrocarbons
To identify the molecular geometry of alkenes and alkynes
Review
Alkanes are saturated hydrocarbons
Saturated hydrocarbons have only single bonds
Examples of alkanes include methane, ethane, propane, 2,3-diethyloctane...
We use system of prefixes to name alkanes
Review
Number of Carbons Prefix
1 meth-
2 eth-
3 prop-
4 but-
5 pent-
6 hex-
7 hept-
8 oct-
9 non-
10 dec-
Review
Name based on longest chain of carbons
Use digits to indicate location of carbon attached to substituents
For example: 5-ethyl-3- methylheptane
How to tell from formula if saturated
In a saturated compound, noncyclic hydrocarbon, the molecular formula will have the form CnHn+2
For example:
C2H6
C8H18
C20H42
Alkenes
Unsaturated hydrocarbons that contain one or more double covalent bonds
Simplest alkene has two carbons joined by a double bond
Ethene
CH2=CH2
Alkynes
Unsaturated hydrocarbons that contain one or more triple covalent bonds
Same naming conventions as alkanes and alkenes
Alkynes with More Than 2 Carbons
Use initial digit to indicate where triple bond is
e.g. 1-hexyne, CH≡C-CH2-CH2-CH2-CH3
2-hexyneCH3-C≡C-CH2-CH2 -CH3
3-hexyneCH3-CH2-C≡C-CH2-CH3
VSEPR Geometry - Unsaturated Hydrocarbons
Carbon with 1 double bond and two single bonds: three groups/regions of electrons around it
Trigonal planar geometry
VSEPR Geometry - Unsaturated Hydrocarbons
Carbon with 2 double bonds: two groups/regions of electrons around it
Linear geometry
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