Alkanes & Alkenes Cheat Sheet

FREE RADICAL SUBSTITUTION Question: Describe the mechanism involved when propane is reacted with chlorine in the presence of UV light to form 1-chloropropane. CI ChChC ChC ChhhChCC·ChhhChCC· ChChC ChC ChhhC·ChC ChhhCChC ChhhC·ChC ChhhC·ChC ChhhCChC ChhhCC propagationreactions produceradicals! INITIATION: 2Ci · CI →UV hh h hh +Ci · → +HCihhhPROPAGATION: +Ci ₂→ +Ci ·hhh hh h Cih Termination: ·Ci+·Ci+ Ci ₂Ci · →hhh hhhCI→ +hhh hhh→hhhhh terminationreactions combineradicals to form astable molecule! Free Radical Substitution remember to write thename of the mechanism! ChhC C h hC C If substituted, If substituted, ChhC Chh h h hCi C hhC Chh h h hCi ChhC Chh h h hCi C hhC Chh h h hCi hh h h hh h h 6 2 : Step 1: List the possible mono-brominated products formed 1-chloropropane 2-chloropropane STEP 2: LABEL AND GROUP THE hydrogen ATOMS THAT WILL GIVE RISE TO ACERTAIN product 3 1 := ChC Chh Ch ChhCh H h hh hxhHHH , Ni catalystr.t & high pressure2 reduction 2CO2 Cl (g) / Br (l), uv light / heat 2 2 excess O (g), heat2 3H o+ F.R.S combustion 2 ChhC Chh h ChC Ch h h hh ChC Ch h hCh3 Secondary radical More stable Most stable Alkanes H2 CHEMISTRY PREDICTING THE RATIO OF DIFFERENT MONO-SUBSTITUTED PRODUCTS REACTION MINDMAP STABILITY OF ALKYL RADICAL Question: State and predict the ratio of the different mono-chlorinated products formed when propane reacts with chlorine under uv. Question: While the statistical ratio between 1- and 2-chloropropane is 3:1, the observed ratio was found to be 1:2. Use the concept of stability of radicals to explain this discrepancy. h h h hh Alkyl groups are electron-donating groups. The moreelectron-donating alkyl groups attached to the carbon radical, the more electron density donated, the more stable theradical and the easier it is to be formed. Primary radical Radical Stability Least stable Tertiary radical Key Concept Answering Technique 1-chloropropane is formed from a primary radical while 2-chloropropane is formed from a secondary radical. With moreelectron-donating alkyl groups attached to the carbonradical, the secondary radical is stabilized to a greaterextent. Hence, 2-chloropropane is formed at higherproportions. To experience why 90% of MACRO students score A/B in A Levels, text us at +65 83662396 :) www.macroacademy.org

CC hciChh δ - CC Chh +h CC Chh -CI: hhhh CC Chh h -CIslowδ +hh hhhhh+ + h+ fast hh hhhCi ChC C h h C h H ChhCh KMnO , dilute H SO , heat4C h h C h ChhCh ChhCh ChhbrChohH ChhChChhCh h hh h X hHH 4 2 electrophilic addition 4Cl / Br dissolved in CCl , r.t22 Br (aq) , r.t2 steam, H PO catalysthigh temperature & pressure43 or ethanolic KOH, heat excess conc H SO ,heat24Al O , heat23 or elimination elimination H , Ni catalystr.t & high pressure2 reduction KMnO , dilute NaOH, cold4 CO2 mild oxidation oxidative cleavage concentrated H SO , cold1. H O2. 422 gaseous HX, r.t (X = Cl, Br, I) h OH H hXH XXH hohH oHohH ChhC Chh h ChC Ch h h hh ChC Ch h hCh3 + + + Secondary carbocationMore stable Most stable h h h hh Alkyl groups are electron-donating groups. The moreelectron-donating alkyl groups attached to the carbocation, the more electron density donated, the more stable thecarbocation and the easier it is to be formed. Primary carbocation Carbocation Stability Least stable Tertiary carbocation Key Concept Answering Technique1-chloropropane is formed from a primary carbocationwhile 2-chloropropane is formed from a secondarycarbocation. With more electron-donating alkylgroups attached to the secondary carbocation, itspositive charge will be dispersed greater and thecarbocation will be stabilized to a greater extent. First step of electrophilic addition results in the formation of a trigonalplanar carbocation intermediate. The nucleophile is thus able to attackfrom the top or bottom face of the carbocation with equal probability.Equal proportion of enantiomers /racemic mixture is formed, whichcancels each other out when rotated through plane-polarized light. C Ch3 3CH CH2+ Ci:- Ci:-h 50%50% C Ci Ch3 3CH CH2 h C Ci 3 Ch3CH CH2 h racemic mixture ChhChr co ₂ + h ₂ oCOhROCR'rO CCCR’rC [O][O][O]CCCCHH [O]CHOOCOHO2co ₂ + h ₂ o[O] Alkenes H2 CHEMISTRY ELECTROPHILIC ADDITION Question: Describe the mechanism involved when propene is reacted with HCl at room temperature to form 2-chloropropane. MAJOR AND MINOR PRODUCT OF E.A REACTION MINDMAP RACEMIC MIXTURE Question: When propene is reacted with HCl at room temperature, two possible products are formed: 1-chloropropance and 2-chloropropane. Explain why 2-chloropropane is the major product. Question: When but-2-ene and HCl react, theproduct mixture is optically inactive underplane-polarized light. Explain. remember to write the name of the mechanism! Answering Technique OXIDATIVE CLEAVAGE For any H1/H2 Chemistry related queries, text us at +65 83662396 :) www.macroacademy.org