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: –H 2 – hydrogenation (usually requires a catalyst & high temperature) –X 2 – I.e. Br 2, Cl 2, F 2 – halogenation I.e. bromination (occurs rapidly at room temperature) –HX I.e. HCl, HBr, HI (hydrohalogenation – occurs at moderate rates at room T) –H 2 O – hydration (requires an acid catalyst, i.e. H 2 SO4) 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 CH 2 =CHCH 3 + H 2 O  + CH 3 CH=CHCH 3 + Cl 2  H-C≡C-CH 2 CH 3 + HBr  + H-C≡C-CH 2 CH 3 + H 2  H 2 C=CHCH 2 CH 3

Addition Examples Benzene + Br 2  no reaction! Aromatics don’t undergo addition! –Not just with X 2 (I.e. Br 2 ), but with anything. –Because the product would be less stable than the resonance double bonds of the benzene!

Uses: Hydrogenated Oils Unsaturated oils can be hydrogenated to 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

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 I 2 to react. The haloalkane chain is nearly colorless Therefore 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 Br 2 –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

Needs an oxidizing agent (which is reduced) –I.e. potassium dichromate (VI) solution (K 2 Cr 2 O 7, in the presence of H 2 SO 4, KMnO 4 ): 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. H 2 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 CO 2 C 6 H 12 O O 2  6 H 2 O + 6 CO 2 –Each C molecule bonded to 2 Os in CO 2, vs. 1 in glucose –Photosynthesis: CO 2 reduced back to glucose 6 H 2 O + 6 CO 2  C 6 H 12 O O 2

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 H 2 O to oxidize ethanol: it loses electrons CH 3 CH 2 OH(g) + H 2 O(l)  CH 3 CO 2 H(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