Ch 11. Unsaturated Hydrocarbons- Alkenes and Alkynes Hydrocarbons with double, triple bonds

Alkanes vs. Alkenes, Alkynes Alkanes: have max # of Hydrogens –saturated with H Alkenes/Alkynes: double/triple bonds between C leading to less Hydrogens-unsaturated with H

Alkene Naming Same prefixes as alkanes, followed by -ene ethene, propene, butene….. Simplest Ethene C2H4

Alkyne Naming Same prefixes followed by –yne: ethyne, propyne, butyne…. Simplest ethyne, C2H2

Location of double/triple bonds Number carbons so that double/triple bonds receive lowest possible location number! Do not number if there is only one, possible location (small alkynes) Beats side chain locations

Name 2-Pentene

Multiple double/triple bonds List location followed by alkane prefix followed by -diene, triene

Name 1,2-pentadiene

Name

Branched unsaturated HC Parentchain needs to contain double/triple bond!!! Naming: 1. Double bond location needs to have lowest C-number, beats lowest location for side chains 2. List all side chains alpha, then list all double bond locations followed by –diene, triene….

Draw in condensed 2-bromo-3-chloro-1-pentene 3,4- dimethyl-4,5,6-octatriene 1,3,5-heptatriyne

Cis/trans configuration Alkene Isomers Cis/trans configuration

Two Types of Double bonds Trans: carbons before and after the double bonds are on opposite (trans) sides Cis: carbons before and after the double bond are on the same (cis) side

Bowtie Structural Drawings for Alkenes Cis-2- butene Trans-2-butene C1 double bond never has cis/trans!!! Name cis/trans if your structural drawing shows it: Kekule and Bowtie only Cis/trans before location number Triple bonds are flat and never have cis/trans

Drawing Double Bonds in Kekule Draw as double line But all molecules, always, start on an upward swing, regardless of double bond location Trans does not disrupt zig-zag!

Drawing Bowtie Improved condensed drawing Double bonds are always horizontal Draw double bonds first Example: 2-pentene in cis an trans

Drawing Triple bonds in Kekule Draw as triple line All molecules start on an upward swing!!! Single bonds before and after triple bond need to have the same angling as the triple bond

Cis and trans in one molecule List cis before trans! draw in Kekule and Bowtie: Cis-2-trans-4-hexadiene

Practice –Draw in Kekule 1-Butene Cis-2-Butene Trans-2-butene 1- Butyne 2-Butyne

Blend of condensed/Kekule

Cyclical Alkenes

Cyclical Alkenes Benzene, famous molecule for process chemistry, has it’s own name! Has alternating single/double bonds What’s the IUPAC name?

Aromatic Many molecules in Nature contain Benzene rings: Aromatic Hydrocarbons Cinnamon

Benzene as a side chain Called Phenyl

4-phenyl-1-hexene

Benzene as a parent

MP/BP trends Generally cis-double bonds lower the MP/BP: disruption of zig/zag There is little difference in MP/BP between single bonds or trans-double bds Triple bonds straighten molecule and raise the boiling beyond single bonds