Chapter 12Chapter 12

Unsaturated Hydrocarbons

(Alkenes)

Where found/usesWhere found/uses

Found in: animal fat, vegetable oil, rubber, Unsaturated fats have less tendency to

increase Used to make drugs, plastics,

Alkenes DefinedAlkenes Defined

Carbon and hydrogen compound containing

General formula

Double bond is more

Bonding in AlkenesBonding in Alkenes

sp2 hybridization, 120O 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 IsomersConstitutional Isomers

More possible isomers for alkenes– 1. – 2. – Butane and 2-methylpropane–

How many isomers are there for C6H12?

Naming AlkenesNaming Alkenes

1. Find longest continuous chain containing 2. Family name changed from –ane to –ene3. Longest chain numbered from the end 4. Substituent names are used as prefixes and

preceded by numbers to indicate location5. 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.

CycloalkenesCycloalkenes

Ring structure with a double bond. Numbering of ring stars at one of the

carbons of the double bond and proceeds

Cis – Trans StereoisomerismCis – 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 StereoisomersVision and Stereoisomers

See box on page 339

ProblemProblem

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

Addition in AlkenesAddition in Alkenes

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

Addition ContinuedAddition Continued

Symmetric addition –

– Catalytic hydrogenation – – Halogenation

Test for alkenes –

Addition to alkenesAddition 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

PolymersPolymers

Chains of (often) Synthetic – Natural – proteins, carbos, nucleic acidsPolyethylenePolyvinylchloride

–

Oxidation of alkenesOxidation of alkenes

By combustion to give By MnO4

- :

By Cr2O72-:

AlkynesAlkynes

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

AromaticsAromatics

Alkanes, -enes, and –ynes are called aliphatic hydrocarbons.

Aromatics have Called aromatic because many have Found in vanilla,

Properties of AromaticsProperties of Aromatics

Benzene ring is Halogens, hydrogen halides, water and

sulfuric acid Combustion of aromatics is

Isomers and NamingIsomers and Naming

Common monosubstituted names–

Disubstituted are named like alkenes.–

Trisubstituted: use numbers

NamingNaming

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 AromaticsReactions of Aromatics

Halogenation:

Nitration:

Sulfonation: Alkylation:

ReationsReations

Selective oxidation– Phenylbutane reacted in the presence of hot,

acidic MnO4- or Cr2O7

2- gives benzoic acid

All 5 types of reactions leave the benzene ring intact.

Fused Ring AromaticsFused Ring Aromatics

“Straight” rings– Napthalene - – Anthracene –

Bent rings– Phenanthrene– Benzanthracene– Benzopyrene– All carcinogens, found in car exhaust, cigarette smoke,

and burnt (barbecued) meat.