Chem Olympiad Orgo Notes PDF

Optical Activity + Stereoisomerism Axial...

Optical Activity + Stereoisomerism Axial chirality chiral center, but axis of no an chirality · : Chiral molecules with o bond rotation is restricted due to steric bulk non-superimposable · : image · a mirror. 2 g. ·. · HI -- · Cahn-Ingold Prelog - Rules (CIP Rules) : - 1. Assign priority - /PPh2 PPhz chiral phosphine BINAP F - - ⑪ -. Put lowest back 2 priority in the 3. If 1 2 , and 3 are Rotating plane polarized light ↳clockwise · : = ( = rotates plane-polarized light right 6) = rotates plane-polarized light left If no place of symmetry total , no. of sterecisomen = 21 Characterising optical activity : · n = no of chiral centers measured at 20 ° ~. angle of rotationa Enantiometric pairs have [x]20a cl = length of sol. opposite configuration at every stereocenter · · 2.. 9 I ↑ conc measured using D-lives of Na lamp A OH = NH2 E cool+ · ~ OH = ↳ NH2 ⑪ CoH · For enantiomers if one has , [x] " = X, the other will have [x] = -X. -enantiomer- I C2 C2 I (2R , 35 , 4R) (23 , 31 , 45) En 1. En. 2 En 1. En. 2 En 1. En 2. 10010 % % 50 % 58 % 96 % 4% Fischer projections enantiomerically enantiomerically · : racemic enriched pure B B = E A -D = C = L & D enantiomeric enantiomeric ratio excess 96 : 4 96 - 4 = 92 % Meso compounds : has chiral centeres + a plane of symmetry ↳ some isomers are achival (3) Ci HH - Ch 1H-D , ! ↓ 1 2. g. same molecule identical ·. Homotopic (carbon center) : only 3 stererisomers - 1800 Hait Br Ch 1 H -D & iMit ! ↳ does not follow the 2" rule. enantiomers : Enantiotopic (carbon center) · Planar chirality : has non-coplanar rings that can't rotate H H H D D H 1 H -D : ↑ * ↑ & * &- &- 11 * &- McN C t CL 2. g. Fus planar chiral i t t diastereomers.. Diastereotopic (carbon center) Prin /- - Ph can be differentiated by NMR Ph S · * Prochiral carbons : carbon that can be converted into a chiral center · e. g. Sp2 carbons & si Re makes substituents 1 2 , 3 go · = , R - Si = makes substituents 1 2 , 3 go & RH · , ↑ depending on R this carbonyl , can be enantiotopic/diastered topic  Conjugation & Aromaticity Conjugation alternating single and : double bonds ↳ every carbon has a p-orbital · Huckel MO for other cyclic rings i-e can be delocalized over the conjugated system Properties of it-systems : 1. it-system is planar 2 all carbons. are sp2 · Huckel's Rule : it -orbital from in-phase of Ip orbitals for. 3 · a planar monocyclic fully conjugated , , ring, * orbital from out-of-phase of Ip orbitals aromatic # 4n 2e (stabilizing = · + = anti-aromatic (destabilizing) - · In e More extensively conjugated systems... * & · Eof HOMOd : it s transition smaller · applying Huckel's rule to multi-fused rings : E of LUMOY ↳.:. absorbs visible wavelengths check every ring for aromaticity 3. : colored C 9. Po ↑ 7. M -7 -V K7 : aromatic · MO analysis of allylic cation + anion · Heteroatoms may have lone pairs in p/sp2 orbitals · * * ↳ these contribute to the -system · 12 n (non-bonding N · I It i anion : " cation I &7 p A. -& Des end carbons have more ve charge i end carbons have more the charge · Aromatic conjugated systems that are cyclic : ↳ Huckel Molecular Orbitals : n ↳ all bonding orbitals filled : very stable  Acidity Basicity Nucleophilicity and Electrophilicity , , · Strong Acids : often used for acid hydrolysis Weak acids · Factors affecting acidity : used as acidic buffers. H-X bond 1 strength # & X larger band longer , = weaker : more acidic. 2 Electronegativity of X XP · Acidity of protons : higher electronegativity = more stable.. More acidic 3. Inductive Effect · EWGs stabilize -ve charge e g · G.. G F 11 Il VS OH OH F # pKa -1 pKa 4 76. 4. Resonance effects 2 9. D B: acidic Hybridisation of atom carrying charge. 5 - ve 2. 9. R = H VS R - CH3 pKa 25 pka is f > Very strong bases : PKaH = PKa of cj acid. base higher-stronger - Charge vs Orbital interactions : Charge electrostatic attraction : 2. g. 15 may be used for Kinetic control ↑ favorable overlap between orbitals strong bases for themodynamic control : Orbital : (15 7). Weak bases : used to create mild basic environment :  Radical Chemistry. 5 Hybridization of atom with radical Radical : unpaired e- sp > sp2 < Sp ↳ wradical dependingonwheretheradic " is easier to form radicals O IT · · - X Persistent radicals : hyper conjugation A · o T - + forms with A · resonance Als phenyl rings la y - e- wants to give e- J ↳ Methyl crowd the radical + N provide groups can lone pair - + 2 wants to gain e- · do not self-terminate e.. of g D G G Roo Hig : Buzsn · · · C1" a 0 RyC" · + · Radical Initiation · s1z D : R- X · RySi · ClyC 1. Thermolysis : 1 2 · radicals are ambiphilic. 2 Photolysis : T 2 nv , 1z ↳ react with both Nu & ED. 3 Redox processes : 2. g. RP + e - > R : Factors of radical stability : 1. Hyperconjugation : · a weak covalent band is usually broken ⑰ "donation of e A- from a parallel compounds for radical initiation : Sta 111 " · Hal o-bond" 1. Peroxides/Diacylperoxides (0-0 bond) 2. %.. 2 Conjugation t-BnOfOt-Bu S ↓ - or hu It-Bud - effect of radical is # - ·G op g g spread RhojOR Koh over 3 atoms ↑ it s & 7 i instead of T 1 R f. 3 Adjacent heteroatoms donating lone pair. 2 Azocompounds Hy2" vs HeC-NHz / CN n- Jo more stable N- & N= Dornus Net + 2 In ↑ (AIBN) Electronegativity of 4. the atom with the radical : HyC HOF' more electronegative & atoms want another. 3 Halogens (usually iodine) : decreasing 2 more badly stability Xor hy I jo I-I 2 4. Nitrites :. 3 Aromatic HomolyticSubstitution Ri hr < RO + No + -& R · Fr + X AR - - HX (termination)" - H*. 5 Organometallic compounds 2 R 9. ·. sush-orIganometal ic - e- common clearable 4 onas. Fragmentation R R R X RE + Redox processes : · R - X + e- ~ [R-X] R : X - R2 >[R - - - X - - - - X + R2 · SH2 reaction. 5 Rearrangement Reactions S = substitution , H = homolytic , 2 = bimolecular 2. 9.. -T Ex2 ~ ② Radical Addition I I in RH f · Anti-Markovnikov rule ↳ more stable radical intermediate formed X R Using BuzSnH radical initiator : as a · RX + X - RinX + · (major) (minor) D BuzSnH a BuzSi X R = + X & i X Re t R BuySiLXIR O (major) (minor) ② < BuySnX + R · Depending on if the radical is Nucor Ele the addition , ③ RTlBusSn a R-H + Buysn" to a carbonyl group differs : - MRz i R3M"hilic 10 : G R Il & · Electrop - Nucleophilic R-  General : BuzSnH R Cl- & R - H AlBN Benzene nalides X = calcogenides isocyanides nitro/xanthates · , , , Reaction has high chemoselectivity · ~ will react with the most reactive functionality e.. g qV - -= 0 BuySnH CHH ↓ O 111g & - -= AIBN 11g& Benzene · radical can be stabilized by carbonyl (conjugation Barton-McCombie deoxygenation alcohol alkane : a · S 1. CS2/base BuzSnH R-OH & R- o - Il SMe > R - H + BuzSn - SMe + 0= c = St 2. Mel AIBN · Mech : r S R-t Di S Hac * · RynfS s Ry Il S - < Ryhisme Siz S-SnBuz - Riv H-SnBus * R _ & R- ↑ S O- SMe Us J & g + > R - H + SnBus Mests- SnBUs > BuySn-SMe + 0= c = >↑ · Barton-McCombie decarboxylation carboxylic acid a alkane Ho -N= "Barton Ester" - - ⑫ = / s DMAP"RA-WT g G 1 R - OH Il PCC BUSn R = ot BuzSn , · 1st step is called "Steglich esterification" DCC : &N = c= N - coupling reagent) HO-N can actually be R-OH - x DMAP : s (for the esterification NOT the , N (nucleophilic catalyst) decarboxylation) it D Steglich = Esterification  - · ↳ & Mech : it - H & M - g & D g N g N Ro - Il H Il DCC N - Ro- Il -N Battacks I #abstractt d DMAP deprotonates DCC Carbon M DMAP I W M Hy M Ga↑ ⑰ H - Zi G 40 - g N T- Il & H R- 16 7 H R- om -N NIN - - R- N Rom I GN P 7 - - G r * & E P - N I M & - 1 HO 17 Nuc Add ↑ S T. add of -N I s ~ I of DMAP i & - I R OH -N -N R- N - La N H area gets kicked R = 1 out I& - S' Bussiv · rT ↓ % u- · ro So g & > R g 24 H- SnBUs U > R-H + BuySn' s 64 produ radical BuzSu coig) regenerated = formation of ~ - s aromatic pyridine BuzSu drives this reaction forward · Birch Reduction reducing Benzene INaNHR - I Mech : fasts NaP Na + nNHz + 2 - [NH3]n I - · T It Log i - Iv~ - - ·E - & Gi · Evespronate KI Cipsopara H I - TT - EDGs promote El Cortho-metal H %.MeNaN E ↳ e. g & > - the most EWG decides the reaction e.. g if NO2 , CHO and OMe are all on the ring , the anion will be stabilized by the NO2 group the fastest ipso -para to NO2 NozCHO Ho : : # Na , NHall One EtcO, EtCH YMe · Wohl-Zeigler Bromination adding : Br to allylic to benzyllic O G initiation resonance stabilized Mech : in-o-omph 2 ph" "W NBS , go & Br - -- (Ph(02)2 O CC14 11 N - Pho. -n - > - also resonance stabilized G NBS -Br 1& A -1 (Ph(02)2 & * II M = I N Br --d 2 - & Br CC14 I (mechanism for benzylic is the same Sandermeyer Reaction diazorene > substituted arene REG - Nen an'Xs Ret + Nen1g14 Mechi xo S NEW single- Xn"tx ↑ RA-NEN