CHM 234: Alkynes Part 2, Week 2 notes
CHM 234: Alkynes Part 2, Week 2 notes CHM 234
Popular in General Organic Chemistry II
verified elite notetaker
Popular in Chemistry
This page Class Notes was uploaded by Alvin Notetaker on Sunday January 24, 2016. The Class Notes belongs to CHM 234 at Arizona State University taught by Pillai in Fall 2015. Since its upload, it has received 30 views. For similar materials see General Organic Chemistry II in Chemistry at Arizona State University.
Reviews for CHM 234: Alkynes Part 2, Week 2 notes
Report this Material
What is Karma?
Karma is the currency of StudySoup.
You can buy or earn more Karma at anytime and redeem it for class notes, study guides, flashcards, and more!
Date Created: 01/24/16
Alkyne Part 2 V Reduction of Alkynes Review 1 Fiatc quot 0 Reduction of Alkynes to Alkanes 0 Reduce by the use of catalytic hydrogenation 0 During the reaction the alkene stage is very dif cult to stop so the nal product is an alkane HZ H IFSCK H n Hg M It V PalC H xozcx quot HjchHz CH3 Hg ngcrH 0 Reduction of Alkynes to Cis Alkenes O Hydrogenation of alkynes can be stopped at alkene stage by using poisoned partially deactivated catalyst O Poisoned Compound I Lindlar s catalyst I NickelBoron complex NizB O This will produce a cis alkene product Jaw z a ass1 H quot 2 0 Reduction of Alkynes to Trans Alkenes O The use of sodium or lithium in liquid ammonia O The reaction stop at the alkene stage because the metal react rapidly With triple bond r 4M Li p a v I V x quotm H f 54543 Mechanism m CH r 39 39 3 CeO CH t wnlec H55 H g gt 12 0 Mia My C33 1 39 l l 52153 1 Addition of an electron to the sp carbon to form a radical anion 2 Protonation of the radical anion to form a Vinylic radical 3 Addition of a second electron forms a Vinyl anion 4 Protonation of the Vinyl anion to form a trans alkene Note Being trans is on a lower energy than cis therefore trans is more stable because of the two bulky groups are on the opposite side Example Na Mg iij r IL 1 x V Paro N VI Hydrohalogenation of Alkynes Review O Goes through electrophilic addition reaction because of weak pi bond 0 Alkyne is less stable and less reactive than alkene at J a 7 1 xi f r 1 I I quotquot 39FF 0quotquot r a CFO 4 SH H r I H i quotr4 M Cr quot sp2 carbocation less s character 4 35 r a n 1 orquot sp carbocation more s character 0 Relative Stabilities of Carbocations a g I Hi quotL i g a 1 V r Rhea gt avg RGH Ro gt RCHI OHI J ERHFG F Kl 4 v H V mp5 F UL Reaction H a V 39 ELY V k h ECJ Hamp i V at o Electrophilic addition of HCl of an alkyne is regioselective 0 Addition follows Markovnikov s rule Mechanism g H Hquot U H 539 Cl v N quotP s a 39939 Ir l HquotCC 39CH3 czg c 39s ltth y a I 31 Cgfgc 5 I v a L1 a 0 Additionally the chlorine atom stabilizes the carbocation by resonance I g 39l 3 O The chlorosubstituted alkene is less reactive than an alkyne because chlorine Withdraws electrons inductively through sigma bond thereby decreasing the nucleophilic character of the double bond Hg 3 RCECH gt Re C 42 Cr 0 With peroxide HBr can be added to a terminal alkyne With antiMarkovnikov 0 Will make a mixture of E and Z isomers CH5 all 0 H26 H3 H CH5 0H2 339 Hz a H fight arcMquot Jr Crc 614304 c Haw LEE 4 W w M H gr H g r VII Hydration of Alkynes Review O AcidCatalyzed Hydration of Alkynes 0 Terminal alkynes are less reactive than internal alkynes With water So mercuric ion Hg2 is used to do the reaction With terminal alkynes This ion is a catalyst P w 39 H x Z aquot quot0 43 C H5 0 a 1 awed man 5 H0 H o z W Heja m 53 H l Enol is bonded to a carboncarbon double bond With an OH group to one of the sp2 carbons Enol rearranges into a ketone 2 Ketone differs from enol from the placement of the double bond and a hydrogen called ketoenol tautomers 3 Tautomers are constitutional isomers that are in rapid equilibrium 4 Equilibrium favors the keto form largely because CO is much stronger than CC T x 5 o eh Hy 7 pDr Li Ha zcraft M at CHEE Hgng H3521 In rm 3C CcC CH1CH 4 chrQ CHl PC HZ CH5 f crc inf ff 3 I C3 l Inw ag J at to D It ht S 39 a H30 CH M 36C H Me 7l If VIII HydroborationOXidation of Alkynes Review o Alkynes can be hydrated antiMarkovnikov by using the hydroborationoxidation reaction 0 Hindered alkyl borane o 9 BBN O Disiamylborane RzBH SiazBH l39 Disinth bemp 3 H had M quot39 i 3 EC39 i wequot Hidekydez o In case of terminal alkyne the keto form is an aldehyde ngQH MNm if G 3C56442 O Mechanism for base catalyzed ketoenol interconversion 39 H 75 WW 4 I2 2 g r r m r quot quotquot H 06 N c H anchcog F 239 f OH V L i 139 H 0 H p H 0 H 0 1339s LSMLQH 1 H302 39 2 IX Halogenation of Alkynes o Bromine and chlorine adds to alkynes to give addition products Br 3 a r a icicfc CZC r 3 1gquot 39 a f x gr g 15713 gr CH3 gr gr b39J 3 C quot c ff 8 1 jquot hilj r clg 5r C X Alkylation of Terminal Alkynes 0 Terminal alkynes can be deprotonated With a strong base which can be used like a nucleophile With an alkyl halide O For an SN2 reaction to proceed in good yield the alkyl halide must be primary With no bulky substituents 0 Secondary and tertiary alkyl halides undergo elimination by an E2 mechanism K CEC MW OpMquotfa6asea Fir R E 19 20 4 quotCECmbm CirCa ems 2 CE39CF39H i or QFCquot 39 at Example Fl I a 2 5 z 3 1 quot7 o Acetylene can undergo alkylation twice F mam 26 L3 39ncs39o E i H 39 JG H C 1 hi Mar agev5 L CH3 gamble VMV C s Mic 5 XI Synthesis Strategies H25 39 LintMarquot Mel 5 J 539 HygijNHa figF A l C 3 Calls wow CHzrahll N S THaDE v 5 mm A I 3 Rquot Swami4 53er Q zh39 l r11 jGHLElar l K5J NmMH2 739 Li Hag Q41 earl er 339quot
Are you sure you want to buy this material for
You're already Subscribed!
Looks like you've already subscribed to StudySoup, you won't need to purchase another subscription to get this material. To access this material simply click 'View Full Document'