Organic Reactions

Organic Reactions Addition, Oxidation, Reduction, Substitution and Elimination

1.) Addition • Only occurs with double or triple carbon bonds (on alkenes + alkynes) • Double (and triple) C bonds are more reactive than single bonds • A bimolecular molecule (A—X) breaks, and each half attaches itself to a C on either side of a = bond • This breaks the = bond to make a single C-C bond

Addition • So called because it makes a bigger molecule (adds more stuff onto the alkene/alkyne) • Things that will undergo addition with an alkene/alkyne: • H2 – hydrogenation (usually requires a catalyst & high temperature) • X2 – I.e. Br2, Cl2, F2 – halogenation I.e. bromination (occurs rapidly at room temperature) • HX I.e. HCl, HBr, HI (hydrohalogenation – occurs at moderate rates at room T) • H2O – hydration (requires an acid catalyst, i.e. H2SO4) • Addition is always exothermic • from energy released by breaking C=C bond

Markovnikov’s Rule • “The Rich Get Richer” • Where Hydrogen = “riches” • I.e. – when HX is attached to an alkene or alkyne, the H is more likely to go on the C that already has the most Hs

Addition Examples • CH2=CHCH3 + H2O + • CH3CH=CHCH3 + Cl2  • H-C≡C-CH2CH3 + HBr + • H-C≡C-CH2CH3 + H2 H2C=CHCH2CH3

Addition Examples • Benzene + Br2 no reaction! • Aromatics don’t undergo addition! • Not just with X2 (I.e. Br2), but with anything. • Because the product would be less stable than the resonance double bonds of the benzene!

Uses: Hydrogenated Oils • Unsaturated oils can behydrogenatedto form solid, saturated fats by the reaction with hydrogen gas in the presence of nickel or platinum as a catalyst. • Ie: Margarine, shortening (Crisco) • Vegetable oils were first hydrogenated for easier transport and storage in 1911. http://www.dvo.com/newsletter/monthly/2006/august/images/Crisco.jpg

Uses: Hydrogenated Oils

Uses: The Iodine Index • The degree of unsaturation in oils can be measured by measuring the amount of iodine that can react with the unsaturated fat or oil by addition. Each mole of C=C requires one mole of I2 to react. • The haloalkane chain is nearlycolorlessTherefore unsaturated hydrocarbon chains will destroy the purple brown color of iodine solutions as long as there are C=C bonds present.

Uses: Bromine Test for Unsaturation • Like Iodine Index, we test for unsaturation with Br2 • Usually done for non-fats, however (i.e. cyclohexene, below, is a non-polar solvent)

2.) (Organic) Oxidation • When an organic molecule is oxidized, it forms more bonds to an Oxygen and fewer bonds to a Hydrogen • LEO says GER  still applies, but it’s easier to think in terms of # of bonds to an oxygen or hydrogen • I.e. • For oxidation to occur, the C must be bonded to at least one H at the start

(Organic) Oxidation • Organic oxidation reactions are written: • The [O] implies that the number of bonds to an oxygen is increasing, but not necessarily the number of oxygens in the molecule • I.e.

(Organic) Oxidation

(Organic) Oxidation • Needs an oxidizing agent (which is reduced) • I.e. potassium dichromate (VI) solution (K2Cr2O7, in the presence of H2SO4, KMnO4): • Oxidizing agent pulls 2 Hs off primary alcohol • Therefore pulls off electrons with the Hs: LEO

(Organic) Oxidation • Oxidizing agent then donates an O to the remaining H • I.e.

Oxidation Examples

3.) (Organic) Reduction • The exact opposite of organic oxidation • Going backwards along this chain: • Forms more bonds to an Hydrogen and fewer bonds to a Oxygen • Done by a reducing agent and a catalyst (I.e. H2 on Platinum catalyst)

(Organic) Reduction • Organic reduction reactions are written: • The [H] implies that the number of bonds to a hydrogen is increasing • This has to increase # of Hs in the molecule • To be reduced, a molecule can’t be saturated with Hs!

Reduction Examples

A Note about Organic Redox • It’s not always obvious where the electrons go (like regular redox) • Sometimes there is no direct transfer of electrons • But there is always a change in Oxidation state. I.e. Reduction:

Uses • Pretty much everything, ever  • Bleach oxidizes pigment molecules until they are no longer the same molecule – lose their colour • Cellular Respiration/Photosynthesis • Cell Resp: Glucose oxidized to CO2 C6H12O6+ 6 O2 6 H2O + 6 CO2 • Each C molecule bonded to 2 Os in CO2, vs. 1 in glucose • Photosynthesis: CO2 reduced back to glucose 6 H2O + 6 CO2 C6H12O6+ 6 O2

Uses • Ethanol conversion in the human body: • People get sick from drinking because the enzyme converting ethanol to acetaldehyde (alcohol dehydrogenase) works faster than the one converting acetaldehyde to acetic acid (acetaldehyde dehydrogenase) • So acetaldehyde builds up – bad stuff

Uses • Old breathalyzer tests: • Ethanol in the bloodstream will come into equilibrium with ethanol in the lungs • I.e. when there’s ethanol in the body, it gets breathed out too • The breathalyzer uses H2O to oxidize ethanol: it loses electrons • CH3CH2OH(g) + H2O(l)  CH3CO2H(l) + 4H+(aq) + 4e- • The 4e- power an electrochemical cell; how much voltage is produced is proportional to how much ethanol is in the lungs and body!

Uses • Problem with old breathalyzer tests: will detect any kind of alcohol (I.e. ethanol from mouthwash, acetone breathed out by some diabetics, compounds in some asthma inhalers!) • New breathalyzers filter out acetone • Breathalyzer tests are confirmed with blood tests – screens for false positives

Organic Reactions