Unsaturated HC’s

The Alkenes and Alkynes

Naming Alkenes & Alkynes

• Have double bonds(enes) triple bonds (ynes)• 1st 5 alkenes/ynes• you must use a # for but and higher• Also name cyclos• Dienes/Trienes

HTPB

• Hydroxyl-terminated polybutadiene

Used in rockets of all kinds

• Like this one

Reactions of alkenes (ynes also but they’re less common)

• Alkenes are much more chemically active than alkanes-why?

• Electron parties

Reactions of alkenes cont’d• Intro video 3 min http://

www.youtube.com/watch?v=1qGPWdm2MlI• The most common type of reaction for alkenes is

addition:• general pattern

– alkene + AB ---> see board• AB can be:

• hydrogen• halogen• water• hydrogen halide

Hydrogenation

• This is the addition of hydrogen• sometimes called catalytic hydrogenation• catalyst is platinum (Pt)• Ex equations• Hydrogenation in food

Halogenation

• Addition of a halogen (what are halogens?)

• no catalyst is required• ex equations

• *addition of a halogen is a good test for unsaturation-esp bromine and iodine

Hydrohalogenation

• Addition of a hydrogen halide (HX) – such as HCl, HBr, HI, HF

• Markovnikov’s rule may apply• no catalyst needed

• ex equations

Hydration

• Addition of water• sulfuric acid catalyst• Markovnikov’s rule may apply

– *Hydration is often confused with hydrogenation

– *conversion of alkenes to alcohols is important in the metabolism of carbohs, fats, proteins. Enzymes are the catalysts.

Practice • Hydration of 1-pentene

• Hydration of cyclohexene

• Hydrochloric acid is added to 1-butene

• Hydrobromic acid is added to cyclopentene

• Hydration of 2-butene

Other reactions of alkenes/ynes

• Oxidation-follows general pattern– HC + oxygen --->carbon dioxide + HOH +

heat

• Polymerization-identical molecules react with each other to produce long chains called polymers– ex: polyethylene, polypropylene

Practice rxns • 1. hydration of 1-butene• 2. hydrogenation of 1-butene• 3. addition of fluorine to 2-pentene• 4. addition of HI to cyclohexene• 5. hydrogenation of cyclobutene• 6. addition of hydrochloric acid to 1-pentene• 7. hydrogenation of cyclopentene• 8. addition of hydrobromic acid to 1-butene• 9. hydration of cyclobutene• 10.addition of iodine to 2-hexene• 11.water is added to 1-pentene

2 rxns for making enes in the lab:

1. Dehydration of an alcohol– what’s a good dehydrating agent?

• Example equations here• 2. Dehydrohalogenation -here, an alkyl halide (RX) is treated with

KOH to remove a H and an adjacent halogen

• ex equations

One step further:

• Dehydrohalogenation can be used to make alkynes if your starting structure has 2 halogens.

• Example equations:

• *this will be a 2-step reaction-you must show the middle step also

practice• Write complete equations for the following reactions. Name everything

except HOH and the catalysts.

• 1.) Ethanol undergoes dehydration• 2.) 2-bromopropane is treated with KOH• 3.) 1-iodoethane undergoes dehydrohalogenation• 4.) 1,1-difluoropropane is treated with excess KOH• 5.) 1-butanol is treated with sulfuric acid• 6.) chlorocyclopropane is treated w/KOH• 7.) 1,1-dibromopentane is treated w/excess KOH• 8.) cyclohexanol is dehydrated (that’s cyclohexane w/an OH)• 9. )1-propanol (3 C’s w/ah OH on the 1st one) is treated w/sulfuric

acid

Fun quiz

• 1. cyclopropanol is treated with sulfuric acid

• 2. 1,1-dichlorohexane is treated with excess KOH

• 3. iodocyclohexane is treated with KOH• 4. 1-butanol is dehydrated• 5. 1-fluorobutane undergoes

dehydrohalogenation

Cis/Trans Isomerism

Stuff I bet you never knew!

Molecules can have an up & a down

• examples:– 2-butene– 3-hexene– 2-pentene– 1-butene– 2-methyl-2-butene– other silly exs

How are cis/trans isomers relevant to us?

• Pheromones (see Justin’s powerpoint)– several types

• sex•alarm• aggregate•aggression

Bees are a good example

The Gypsy Moth Story

• The female gypsy moth secretes cis-glyplure to attract males

• expt with male moths in a cage and cis-glyplure on a Q-tip

• the UAB chemist’s moth problem• gypsy moths aren’t here-YET• they will react to 1 molecule of the

pheromone

Cis/trans in vision

• There is a chemical vital to human vision, in the liver it’s called Rhodopsin

• Rhodopsin comes from Greek word for “rose-colored” b/c it has a reddish color in the dark which fades when exposed to light

• Rhodopsin in the liver makes its way into the retina where it’s called cis-retinal (or Vitamin A)

Cis/trans in vision cont’d

• Once in the retina, light hits the cis-retinal and it’s changed into trans-retinal

• Interesting note:– the energy reqd to make this change is

250kJ/mole. A photon of sunlight has 165-293 kJ/mole of energy. If we were a little closer or further away from the sun, we couldn’t see anything.

Cis/trans in vision con’td

• When the cis-retinal changes to the trans form, the shape of the molecule changes and it’s released from the protein that holds it.

• Ions are produced and they flow through the optic nerve. We see this as light.

• Later, an enzyme changes the trans back to cis, it binds back to the protein and awaits the next exposure to light.

Cis/trans in taste

• We only taste one and not the other b/c receptors on tongue only fit one

• Ex: cis/trans fumaric acid• trans-fumaric acid maleic acid

• (cis-fumaric acid)

Cis/trans in odors

• The geometry of molecules is a main determinant of odor

• must fit in olfactory receptors• essential oils of plants give them their

pleasant odors – rose, citronella, verbena

What about trans fatty acids?

• Fatty acids can be either cis or trans• trans fatty acids are bad• they raise bad cholesterol levels• Nerdy video with really good info! 6 min• http://www.youtube.com/watch?v=TNrMId

zvRww

Where do we find trans FA’s?

• Hydrogenation creates these bad fatty acids.

• They are worse for the body than butter and animal fat (lard)

• what kinds of foods contain trans fatty acids?

• LOTS!

What about rubber?

• Rubber trees make both cis and trans forms of rubber

• ex: smart and stupid balls• cis bounces, trans doesn’t• trans rubber is used to make tires b/c cis is

too bouncy

Preparation of unsatd HC’s

• Fossil fuels contain satd & unsatd HC’s• we can increase the yield of unsatds

through a process called cracking• Def cracking: when long, straight-chained

HC’s are broken down in to smaller pieces• 2 types of cracking:

– thermal– catalytic

Car fuels• Def fuel: any chemical that can be used in the operation

of an internal combustion engine• How a 2 stroke engine works• http://www.youtube.com/watch?v=LuCUmQ9FxMU&feat

ure=PlayList&p=0D07C0CE4E904876&playnext=1&playnext_from=PL&index=10

• Marshall Brain/s tater gun• http://videos.howstuffworks.com/howstuffworks/190-how-

engines-work-video.htm• what makes the “best” fuels?

– Those that produce lots of power and not much knocking

Knocking!

• Def: a premature ignition due to heat and not spark

• why is knocking bad?– Loss of energy– engine damage– *diagram here– how does a diesel engine work? – Biodiesel video 3.5 min– http://videos.howstuffworks.com/science-channel/504

4-invention-nation-biodiesel-video.htm

Gasoline additives• Tetraethyl lead-was in “leaded” gas in the

70’s and earlier• why was it added?• Why is it not added now?

Lead poisoning• We can eliminate only about 2 mg of Pb/day

through the kidneys• excess lead is stored in bones and soft tissues-

lead poisoning video 2 min• http://videos.howstuffworks.com/discovery/3488

6-howstuffworks-show-lead-poisoning-video.htm• And in kids video 1.5 min• http://videos.howstuffworks.com/discovery/3488

7-howstuffworks-show-lead-poisoning-in-kids-video.htm

Common names of enes/ynes

• The IUPAC naming system is fairly new. Many common names predate IUPAC and are still used today.

• Ethyne-acetylene• Propene-propylene• ethene-ethylene

ethylene

• produced in many fruits and vegs as they ripening

• acts as a hormone to enhance the softening process

Alkynes

• ethyne is the most common alkyne• also called acetylene• early cars had carbide lamps• miners and cavers also used them• 2 ways to make ethyne:

Making acetylene

• One way:– Heating methane to very high temps in the

absence of oxygen

• 2CH4 -----> HC=CH + 3H2

Making acetylene

• Another way:– hydration of calcium carbide (go outside!)

– CaC2 + 2HOH ----> HC=CH + Ca(OH)2

– *be sure you can write and name everything in these 2 equations :)