Cia peb siv qhov yooj yim tshaj plaws uas tsis sib haum xeeb thiab tsis muaj cov hydrocarbon thiab qhov yooj yim tshaj plaws symmetrical thiab unsaturated hydrocarbon. Lawv yuav ua raws li propene thiab butene-2. Cov no yog cov alkenes, thiab lawv nyiam ua rau muaj kev cuam tshuam ntxiv. Cia, piv txwv li, nws yog qhov sib ntxiv ntawm hydrogen bromide. Nyob rau hauv cov ntaub ntawv ntawm butene-2, tsuas yog ib qho khoom ua tau - 2-bromobutane, uas ntawm cov pa roj carbon atoms bromine yuav txuas - lawv txhua tus sib npaug. Thiab nyob rau hauv cov ntaub ntawv ntawm propene, muaj ob txoj kev xaiv: 1-bromopropane thiab 2-bromopropane. Txawm li cas los xij, nws tau sim ua pov thawj tias 2-bromopropane pom tau zoo nyob hauv cov khoom ntawm cov tshuaj tiv thaiv hydrohalogenation. Tib yam muaj tseeb rau cov tshuaj tiv thaiv hydration: propanol-2 yuav yog cov khoom tseem ceeb.
Los piav qhia tus qauv no, Markovnikov tsim txoj cai, uas yog hu ua nws lub npe.
Markovnikov txoj cai
Siv rau cov alkenes tsis sib xws thiab alkynes. Thaum cov dej los yog hydrogen halides txuas rau cov molecules, lawv cov hydrogen raug xa mus rau feem ntau hydrogenated carbon atom nyob rau hauv ob daim ntawv cog lus (uas yog, ib tug uas muaj feem ntau carbon atoms rau nws tus kheej). Qhov no ua haujlwm rau qhov piv txwv propene kawg: lub hauv paus carbon atom nqa tsuas yog ib qho hydrogen, thiab ib qhouas nyob rau ntawm ntug - ntau npaum li ob, yog li hydrogen bromide clings mus rau cov huab cua carbon atom nrog hydrogen, thiab bromine mus rau hauv nruab nrab ib, thiab 2-bromopropane yog tau.
Tau kawg, txoj cai tsis yog tawm ntawm huab cua nyias, thiab muaj ib qho kev piav qhia rau nws. Txawm li cas los xij, qhov no yuav xav tau kev kawm ntxaws ntxiv ntawm cov tshuaj tiv thaiv.
Ntxiv cov tshuaj tiv thaiv mechanism
Cov tshuaj tiv thaiv tshwm sim hauv ntau theem. Nws pib nrog cov organic molecule raug tawm tsam los ntawm hydrogen cation (ib qho proton, feem ntau); nws tawm tsam ib qho ntawm cov pa roj carbon atoms hauv ob daim ntawv cog lus, vim tias cov hluav taws xob ceev muaj ntau ntxiv. Ib qho txiaj ntsig zoo proton yeej ib txwm nrhiav rau thaj chaw uas muaj hluav taws xob ntau ntxiv, yog li nws (thiab lwm yam khoom uas coj zoo ib yam) yog hu ua electrophile, thiab cov tshuaj tiv thaiv mechanism, feem, yog ib qho ntxiv electrophilic.
Ib tus proton tawm tsam cov molecule, nkag mus rau hauv nws, thiab tsim cov carbonium ion zoo. Thiab ntawm no, ib yam nkaus, muaj ib qho kev piav qhia rau Markovnikov txoj cai: qhov ruaj khov tshaj plaws ntawm txhua qhov ua tau carbcations yog tsim, thiab theem nrab cation yog ruaj khov dua li thawj, tertiary ruaj khov dua qhov thib ob, thiab lwm yam (muaj. muaj ntau txoj hauv kev kom ruaj khov carbcation). Thiab tom qab ntawd txhua yam yog ib qho yooj yim - tus nqi tsis zoo halogen, lossis ib pawg OH txuas nrog rau tus nqi zoo, thiab cov khoom kawg tau tsim.
Yog tias thaum xub thawj qee qhov tsis yooj yim carbocation tau tsim dheev, nws tuaj yeem hloov kho kom nws yooj yim thiab ruaj khov (ib qho txiaj ntsig zoo cuam tshuam nrog qhov no, uas qee zaum thaum lub sijhawm cov tshuaj tiv thaiv ntxiv halogen lossis hydroxyl pab pawg xaus rau lwm lub atom. tag nrhocarbon uas tsis muaj ob daim ntawv cog lus, tsuas yog vim qhov zoo ntawm cov carbocation hloov mus rau qhov chaw ruaj khov tshaj plaws).
Yuav ua li cas cuam tshuam txoj cai?
Vim nws yog raws li kev faib tawm ntawm electron ceev hauv carbocation, ntau yam hloov pauv hauv cov organic molecule tuaj yeem cuam tshuam. Piv txwv li, ib pawg carboxyl: nws muaj oxygen hooked rau carbon los ntawm ob daim ntawv cog lus, thiab nws rub lub electron ceev ntawm ob daim ntawv cog lus rau nws tus kheej. Yog li ntawd, nyob rau hauv acrylic acid, ib tug ruaj khov carbocation yog nyob rau hauv lub kawg ntawm cov saw (tawm ntawm cov carboxyl pawg), uas yog, ib tug uas yuav tsis tshua muaj txiaj ntsim nyob rau hauv ib txwm tej yam kev mob. Qhov no yog ib qho piv txwv uas cov tshuaj tiv thaiv tawm tsam Markovnikov txoj cai, tab sis cov txheej txheem ntawm electrophilic ntxiv yog khaws cia.
Peroxide Harash effect
Xyoo 1933, Morris Harash tau ua tib yam tshuaj tiv thaiv ntawm hydrobromination ntawm unsymmetrical alkenes, tab sis nyob rau hauv lub xub ntiag ntawm peroxide. Thiab ib zaug ntxiv, cov khoom siv tshuaj tiv thaiv tau tawm tsam Markovnikov txoj cai! Cov nyhuv Kharash, raws li nws tau hu ua tom qab, muaj nyob rau hauv lub fact tias nyob rau hauv lub xub ntiag ntawm peroxide, tag nrho cov tshuaj tiv thaiv mechanism hloov. Tam sim no nws tsis yog ionic, zoo li ua ntej, tab sis radical. Qhov no yog vim qhov tseeb tias peroxide nws tus kheej ua ntej tawg mus rau hauv cov radicals, uas ua rau muaj kev sib txuas lus. Tom qab ntawd ib qho bromine radical yog tsim, ces ib qho organic molecule nrog bromine. Tab sis cov radical, zoo li cov carbocation, ruaj khov dua - theem nrab, yog li bromine nws tus kheej yog qhov kawg ntawm cov saw.
Ntawm nokwv yees piav qhia txog cov nyhuv Kharash hauv tshuaj lom neeg.
Kev xaiv
Nws tsim nyog hais tias cov nyhuv no tsuas yog ua haujlwm thaum ntxiv hydrogen bromide. Nrog hydrogen chloride thiab hydrogen iodide, tsis muaj dab tsi tshwm sim. Txhua qhov kev sib txuas no muaj nws tus kheej vim li cas.
Hauv hydrogen chloride, kev sib raug zoo ntawm hydrogen thiab chlorine muaj zog heev. Thiab yog hais tias nyob rau hauv radical tshua pib los ntawm kub thiab lub teeb muaj txaus lub zog los rhuav nws, lub radicals tsim thaum lub sij hawm decomposition ntawm peroxide yog xyaum tsis muaj peev xwm ua qhov no, thiab cov tshuaj tiv thaiv nrog hydrogen chloride qeeb heev vim cov nyhuv peroxide.
Hauv hydrogen iodine, daim ntawv cog lus tawg yooj yim dua. Txawm li cas los xij, iodine radical nws tus kheej hloov tawm kom muaj qhov tsis tshua muaj tshwm sim, thiab cov nyhuv Harash dua yuav luag tsis ua haujlwm tag nrho.
