Unsaturated Hydrocarbons Double and Triple bonds between Carbons

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 CarbonsPrefix 1meth- 2eth- 3prop- 4but- 5pent- 6hex- 7hept- 8oct- 9non- 10dec-

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 C n H n+2 For example: C 2 H 6 C 8 H 18 C 20 H 42

Alkenes Unsaturated hydrocarbons that contain one or more double covalent bonds Simplest alkene has two carbons joined by a double bond Ethene CH 2 =CH 2

Alkenes with More Carbons Propene CH 2 =CH-CH 3

Alkenes with More Carbons Butene CH 2 =CH-CH 2 -CH 3 & CH 3 -CH=CH-CH 3

Alkenes with More Carbons Pentene

Alkene with Substituents Same basic rules as for alkanes

Alkene with Substituents 5, 5 - diethyl - 2, 6, 7- trimethyl octene

Alkene with more than one double bond 1, 3 - butadiene

Alkene with more than one double bond 6-methyl-1,4,8-nonatriene

Alkynes Unsaturated hydrocarbons that contain one or more triple covalent bonds Same naming conventions as alkanes and alkenes

Alkynes with More Than 2 Carbons Propyne CH≡C-CH3

Alkynes with More Than 2 Carbons Use initial digit to indicate where triple bond is e.g. 1-hexyne, CH≡C-CH 2 -CH 2 -CH 2 - CH 3 2-hexyne CH 3 -C≡C-CH 2 -CH 2 - CH 3 3-hexyne CH 3 -CH 2 -C≡C-CH 2 -CH 3

Alkynes with Substituents 7-methyl-3-octyne CH 3 -CH-CH 2 -CH 2 -C≡C-CH 2 -CH 3 | CH 3

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

VSEPR Geometry - Unsaturated Hydrocarbons Carbon with 1 double bonds and 1 single bond: two groups/regions of electrons around it Linear geometry