Chapter 12 Unsaturated Hydrocarbons (Alkenes)

Where found/uses Found in: animal fat, vegetable oil, rubber, Unsaturated fats have less tendency to increase Used to make drugs, plastics,

Alkenes Defined Carbon and hydrogen compound containing General formula Double bond is more

Bonding in Alkenes sp 2 hybridization, 120 O bond angle, 3 equivalent bonds Two types of bonds – Sigma bond (  ) - Strong – Pi bond (  ) – Weak Overlap of unused p orbital creates the double bond

Constitutional Isomers More possible isomers for alkenes – 1. – 2. – Butane and 2-methylpropane – How many isomers are there for C 6 H 12 ?

Naming Alkenes 1. Find longest continuous chain containing 2. Family name changed from –ane to –ene 3. Longest chain numbered from the end 4. Substituent names are used as prefixes and preceded by numbers to indicate location 5. A compound with two double bonds is a diene and the name ends –diene. The name includes numbers to show both locations of the double bonds.

Cycloalkenes Ring structure with a double bond. Numbering of ring stars at one of the carbons of the double bond and proceeds

Cis – Trans Stereoisomerism Double bonds This allows for There are 2 possible 2-butene compounds, each with different geometric arrangements. – Difference is in the configuration – both compounds have the same connectivity.

Vision and Stereoisomers See box on page 339

Problem Which of the following exist as a pair of cis and trans isomers? –

Addition in Alkenes Double bond is reactive enough to allow the addition of – Hydrogen – – – Water

Addition Continued Symmetric addition – – Catalytic hydrogenation – – Halogenation Test for alkenes –

Addition to alkenes Asymmetric addition – Addition of water in the presence of Markovnikov Rule – The major product is the one formed when the hydrogen from the asymmetric reagent adds to the carbon of the double bond that has more hydrogen. HCl + propene

Polymers Chains of (often) Synthetic – Natural – proteins, carbos, nucleic acids Polyethylene Polyvinylchloride –

Oxidation of alkenes By combustion to give By MnO 4 - : By Cr 2 O 7 2- :

Alkynes Unsaturated hydrocarbons with a General formula: Similar chemistry to alkenes Ending changed to sp hybridization, 180 o bond angle Single sigma bond, two pi bonds Addition reactions follow Markovnikov’s rule

Aromatics Alkanes, -enes, and –ynes are called aliphatic hydrocarbons. Aromatics have Called aromatic because many have Found in vanilla,

Properties of Aromatics Benzene ring is Halogens, hydrogen halides, water and sulfuric acid Combustion of aromatics is

Isomers and Naming Common monosubstituted names – Disubstituted are named like alkenes. – Trisubstituted: use numbers

Naming If there is a large aliphatic chain attached to the ring, use the word phenyl to show the benzene – 2-methyl-3-phenylbutane The group

Reactions of Aromatics Halogenation: Nitration: Sulfonation: Alkylation:

Reations Selective oxidation – Phenylbutane reacted in the presence of hot, acidic MnO 4 - or Cr 2 O 7 2- gives benzoic acid All 5 types of reactions leave the benzene ring intact.

Fused Ring Aromatics “Straight” rings – Napthalene - – Anthracene – Bent rings – Phenanthrene – Benzanthracene – Benzopyrene – All carcinogens, found in car exhaust, cigarette smoke, and burnt (barbecued) meat.