Alkenes

1: identify longest C chain with C=C 2: no. C, C=C should have the lowest no. (thro both Cs) 3: 2 C=C: dienes; 3 C=C: trienes

less stable due to steric strain b/w 2 aklyl groups in cis

Electrophile is an e- pair acceptor that is attracted to e- rich site It is e- deficient • +ve charge • partial +ve charge • incomplete orbit

Step 1: Addition of electrophile (𝛿+H of HBr cuz Br > electro-ve than H) slow step … (look at notes) Step 2: Nucleophilic attack by Br- fast step • Name mechanism • Indicate 𝛿- & 𝛿+ if any • Use full arrows to show movement of e- • Show lp of e- on nucleophile • indicate slow/fast step • draw formula for any intermediate • draw prod (identify major n minor)

Major prod: when electrophile is added to produce more stable carbocation intermediate For HX: add to C with more H For others: add to C with most R When drawing a mechanism, draw more stable one

More R - more stable - form faster Reason: R is e- donating -> disperses the +ve charge on C -> stabilises carbocation vs e- withdrawing -> intensifies the +ve charge on C -> destabilises the carbocation

Addition of hydrogen halides (HX) C=C + HX —-DRY HX (g) —–> C - C | | H X * must be (g), if it’s (aq), it’ll form alcohol Reactions with halogens (in CCl4) Conditions: dark, rm temp (prevent FRS) C=C + X2 —-CCl4 —–> C - C | | X X *CCl4 is inert Reactions with halogens (in H2O) —————- (CHECK NOTES for electrophilic addition mechanism) C=C + X2 + H2O ———> C - C + HX | | X OH Reagents: X2 in water OR X2(aq) Conditions: dark, rm temp

positive charge where an electron or two is absent negative charge because we have an extra electron or two

Addition of water (lab method) - *mechanism too C=C + H2O —- 1. cold conc H2SO4 2. H2O, heat —> C - C | | H OH Mechanism: Step 1a: addition of e-phile (H in H2SO4) Step 1b: nucleophilic attack by -OSO2OH Step 2: Hydrolysis Addition of water (industrial method) C=C + H2O(g) —- H3PO4 on silica, high temp, high pressure —> C - C | | H OH

mild oxi C=C + H2O + [O] —– KMnO4(aq), NaOH(aq), cold ——> C - C | | OH OH Observations: purple KMnO4 decolourised + brown-black ppt of MnO2 observed strong oxi - C=C —– KMnO4(aq), H2SO4(aq), heat ——> ketones OR/& carboxylic acid OR/& CO2 & H2O Rule: ~ Cleave C=C and put O on C= ~ Replace H directly attached to C= with OH ~ anything formed that is not ketones/carboxylic acid, just convert to CO2 & H2O Observations: purple KMnO4 decolourised + CO2 gas evolved • C=C —– KMnO4(aq), NaOH(aq), heat ——> ketones OR/& ‘carboxylic acid’ just that OH is O-Na+ instead OR/& Naa2CO3 & H2O Same rule just instead of putting OH, replace with O-Na+

C=C + H2(g) — Ni, heat /Pd/Pt —-> C - C | | H H • amt of H2 reactant per mole of alkene is a measure of the no. of C=C bonds present cuz 1 mol of C=C bond requires 1 mol of H2 to reduce

Addition polymers are formed with monomer containing C=C eg poly(ethene) monomer struc: C=C polymer struc/formula -[- C - C -]- n

• Dehydrohalogenation of halogenoalkanes C - C —KOH in ethanol, heat—-> C=C + HX | | H X Reagents: KOH in ethanol/ethanolic KOH/alcoholic KOH/NaOH in ethanol • Elimination of H2O from alcohols C - C —excess conc H2SO4, heat—-> C=C + H2O | | OH H Reagents: excess conc H2SO4, heat OR Al2O3, heat OR H3PO4, heat

Saytzeff’s rule: preferred prod - C=C with greater no. of alkyl grp (most sub. alkene)

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• reagents and conditions • +ve and -ve observations • chemical test for any gas evolved • eqns (if qn requires)

E- withdrawing due to the difference in electronegativity between carbon and hydrogen. Because carbon is more electronegative, it pulls electron density