Transcript Cis/Trans
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=1qGPWdm2M lI • 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 cisglyplure to attract males • expt with male moths in a cage and cisglyplure 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 cisretinal and it’s changed into trans-retinal • Interesting note: – the energy reqd to make this change is 250kJ/mole. A photon of sunlight has 165293 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&play next_from=PL&index=10 • Marshall Brain/s tater gun • http://videos.howstuffworks.com/howstuffworks/190-howengines-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/sciencechannel/5044-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 tissueslead 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-kidsvideo.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 :)