Alkenes
Alkenes Each member contains one double covalent bond between two C atoms. Draw condensed structural formulas of first three members of alkenes family. Alkenes are unsaturated aliphatic hydrocarbons. Members of alkenes family create homologous series. That means that every next member has extra -CH 2 - unit. General formula : C n H 2n
What compound is the first member of alkene family? Can we have more than one double bond in a carbon chain? If so, how would we call these compounds?
Properties Non-polar compounds - soluble in non-polar solvents Gasses, liquids and solids More reactive than alkanes, thanks to double bond
Naming Alkenes Naming: Substituents + number of C atoms + ene prefix root suffix Prefix: alkyl groups, halogens Remember: Suffix ene : tells you that one double bond is present
Alkene Homologous Series (C1-C2 double bond) # of C Root 2 Eth- Ethene Name (Root + ene) 3 Prop- Propene 4 But- 1-butene 5 Pent- 1-pentene Condensed structural formula 6 Hex- 7 Hept- 8 Oct- CH 3 - CH 2 - CH 2 - CH 2 - CH 2 - CH 2 - CH = CH 2 9 Non- CH 3 - CH 2 - CH 2 - CH 2 - CH 2 - CH 2 - CH 2 - CH = CH 2 10 Dec- CH 3 - CH 2 - CH 2 - CH 2 - CH 2 - CH 2 - CH 2 - CH 2 - CH = CH 2
# of C Root Name (Root + ene) Condensed structural formula 2 Eth- Ethene CH 2 = CH 2 3 Prop- Propene CH 3 - CH = CH 2 4 But- 1-butene CH 3 - CH 2 - CH = CH 2 5 Pent- 1-pentene CH 3 - CH 2 - CH 2 - CH = CH 2 6 Hex- 1-hexene CH 3 - CH 2 - CH 2 - CH 2 - CH = CH 2 7 Hept- 1-heptene CH 3 - CH 2 - CH 2 - CH 2 - CH 2 - CH = CH 2 8 Oct- 1-octene CH 3 - CH 2 - CH 2 - CH 2 - CH 2 - CH 2 - CH = CH 2 9 Non- 1-nonene CH 3 - CH 2 - CH 2 - CH 2 - CH 2 - CH 2 - CH 2 - CH = CH 2 10 Dec- 1-decene CH 3 - CH 2 - CH 2 - CH 2 - CH 2 - CH 2 - CH 2 - CH 2 - CH = CH 2
Isomers Branched differently (similar to alkanes) chain isomerism Different position of double bond positional isomerism Different position of groups around double bond cis-trans isomers
Naming Alkenes Step 1: Identify the longest continuous chain that contains the double bond. CH 2 = C CH 2 CH 2 CH 3 I CH 2 I CH 3 CH 2 = C CH 2 CH 2 CH 3 I CH 2 I CH 3
Step 2: Number the parent carbon chain beginning at the end nearest the double bond. CH 3 CH = CH CH 2 CH 3 CH 3 CH = CH CH 2 CH 3
If the double bond is in equal distance to both ends of the parent chain A) CH 3 CH = CH CH 2 l Cl B) CH 2 CH = CH CH 2 l l F Cl A) begin the numbering from the end closer to a substituent. B) begin the numbering from the end at which the substituent is first in alphabetical order.
Step 3: Identify and locate the branches. Put branches in alphabetical order Use multiplying prefixes (di-, tri-, tetra-..) if needed Step 4: Put the name together
Sample Problem 1 1. CH 3 CH = CH CH 2 CH 2 CH 3 2. CH 3 CH 2 CH 2 CH 2 CH = C CH 3 І CH 2 CH 2 CH 3 3. CH 3 CH CH 2 CH 2 C = CH CH 3 І І CH 3 CH 2 CH 2 CH 3
Sample Problem 1 - answers 1. 2-hexene 2. 4-methyl-4-nonene 3. 6-methyl-3-propyl-2-heptene
Sample Problem 2 1. 2. 3. 4. CH 3 CH = CH CH 2 CH CH 3 l F CH 3 C = CH CH CH 2 CH 3 l l Cl Br CH 3 CH CH CH CH = C CH 3 l l l І Br Cl Cl CH 2 CH 2 CH 2 I CH 3 CH 2 F l I CH 3 CH CH CH C = C CH 3 І I І CH 3 F CH 2 CH 2 CH 3
Sample Problem 2 - answers 1. 5-flouro-2-hexene 2. 4-bromo-2-chloro-2-hexene 3. 8-bromo-6,7-dichloro-1-iodo-4- methyl-4- nonene 4. 4-ethyl 2,5-difluoro-6-methyl-3-propyl-2- heptene
Cis-Trans (Geometric) Isomers Cis-trans isomers occur when different groups of atoms are arranged around the double bond. The atoms around a single bond can rotate, but the atoms around a double bond cannot this will result in different geometric structures. How might you distinguish between two such isomers in the lab?
Trans-Isomers Trans Isomer the two larger groups attached to the double bond are on opposite sides of the double bond Ex. trans-2-butene Cis-Isomers Cis Isomer the two larger groups attached to the double bonds are on the same side of the double bond Ex. cis -2-butene
Sample Problems 3
Sample Problems 3 - answers 1. cis-3-heptene 2. trans-4-octene 3. cis-1,2-dichloroethene 4. It is not cis-trans isomer (propene)
Drawing Alkenes Step 1: Identify the main chain and draw it as skeletal structure. Step 2: Number it. (Make sure that the double bond is at the right spot.) Step 3: Identify all substituents and attach them to the parent chain. Step 4: Fill in hydrogen atoms. (Remember to count to four)
Draw the following Sample Problems 4 1. 4-methyl-2-pentene 2. 3-ethyl-2,4-dimethyl-6-propyl-1-nonene 3. 2,4-dichloro-3,3-dimethyl-1-butene 4. 2-methylpropene *Why is there no number to state the location of this double bond?
Sample Problems 4 answers